Freescale Semiconductor, Inc. reserves the right to change the detail specifications,
as may be required, to permit improvements in the design of its products.
Document Number: MC33972
Rev. 19.0, 3/2012
Freescale Semiconductor
Technical Data
© Freescale Semiconductor, Inc., 2009-2012. All rights reserved.
Multiple Switch Detection
Interface with Suppressed
Wake-up
The 33972 Multiple Switch Detection Interface with suppressed
wake-up is designed to detect the closing and opening of up to 22
switch contacts. The switch status, either open or closed, is transferred
to the microprocessor unit (MCU) through a serial peripheral interface
(SPI). The device also features a 22-to-1 analog multiplexer for reading
inputs as analog. The analog input signal is buffered and provided on
the AMUX output pin for the MCU to read.
The 33972 device has two modes of operation, Normal and Sleep.
Normal mode allows programming of the device and supplies switch
contacts with pull-up or pull-down current as it monitors switch change
of state. The Sleep mode provides low quiescent current, which makes
the 33972 ideal for automotive and industrial products requiring low
sleep-state currents.
Features
• Designed to operate 5.5 V ≤ VPWR ≤ 26 V
• Switch input voltage range -14 V to VPWR, 40 V Max
• Interfaces directly to MPU using 3.3 V / 5.0 V SPI protocol
• Selectable wake-up on change of state
• Selectable wetting current (16 or 2.0 mA)
• 8 programmable inputs (switches to battery or ground)
• 14 switch-to-ground inputs
• Typical standby current - VPWR = 100 μA and VDD = 20 μA
• Active interrupt (INT) on change-of-switch state
Figure 1. 33972 Simplified Application Diagram
MULTIPLE SWITCH
DETECTION INTERFACE
EW SUFFIX (Pb-FREE)
98ARH99137A
32-PIN SOICW
ORDERING INFORMATION
Device Temperature
Range (TA)Package
MC33972TEW/R2
-40 °C to 125 °C 32 SOICW
MC33972ATEW/R2
MC33972ATEK/R2 32 SOICW EP
33972/A/T
EK SUFFIX (Pb-FREE)
98ASA10556D
32-PIN SOICW EP
VBAT
SP0
SP1
SP7
SG0
SG1
SG12
SG13
VPWR
VDD
WAKE
SI
CS
SO
INT
AMUX
GND
MOSI
SCLK
CS
MISO
INT
AN0
33972
MCU
SCLK
POWER SUPPLY
LVI
ENABLE
WATCHDOG
RESET
VDD
VBAT
VDD
VBAT
Analog Integrated Circuit Device Data
2Freescale Semiconductor
33972
DEVICE VARIATIONS
DEVICE VARIATIONS
Table 1. Device Variations
Device Switch Input Voltage Range Reference Location
33972 -14 to 38 VDC 5, 6
33972A -14 to 40 VDC 5, 6
Analog Integrated Circuit Device Data
Freescale Semiconductor 3
33972
INTERNAL BLOCK DIAGRAM
INTERNAL BLOCK DIAGRAM
Figure 2. 33972 Simplified Internal Block Diagram
+
‚
5.0 V
125 kΩ
VDD
Analog Mux
Output
VPWR, VDD, 5.0 V
POR
Oscillator
Clock Control
Bandgap
Sleep PWR
40 μA
SPI Interface
and Control
WAKE Control
INT Control
Temperature
Monitor and
Control
MUX Interface
SP0
SP1
SG0
SP2
SP3
SP4
SP5
SP6
SP7
SG2
SG1
SG3
SG4
SG5
SG6
SG7
SG8
SG9
SG10
SG11
SG12
SG13
WAKE
INT
SCLK
CS
SO
AMUX
SI
VDD
VPWR
GND
VPWR
5.0 V
VPWR
5.0V
5.0 V
VPWR
VDD
VDD
and
5.0 V
+
‚
4.0 V
Comparator
To
VPWR SG0
SPI
Ref
2.0
mA
16.0
mA
VPWR
5.0 V
125 kΩ
VDD
2.0 +
‚
4.0V
Comparator
To
VPWR SP7
SPI
Ref
mA
2.0
mA
16.0
mA
16.0
mA
VPWR
2.0 +
‚
4.0 V
Comparator
To
VPWR SP0
SPI
Ref
mA
2.0
mA
16.0
mA
16.0
mA
VPWR
+
‚
4.0 V
Comparator
To
VPWR SG13
SPI
Ref
2.0
mA
16.0
mA
VPWR
Analog Integrated Circuit Device Data
4Freescale Semiconductor
33972
PIN CONNECTIONS
PIN CONNECTIONS
Figure 3. 33972 Pin Connections
Table 2. 33972 Pin Definitions
A functional description of each pin can be found in the Functional Pin Description section beginning on page 10.
Pin Number Pin Name Pin Function Formal Name Definition
1GND Ground Ground Ground for logic, analog, and switch to battery inputs.
2SI Input SPI Slave In SPI control data input pin from the MCU to the 33972.
3SCLK Input Serial Clock SPI control clock input pin.
4CS Input Chip Select SPI control chip select input pin from the MCU to the 33972. Logic [0}
allows data to be transferred in.
5 – 8
25 – 28
SP0 – 3
SP4 – 7
Input Programmable
Switches 0 – 7
Programmable switch-to-battery or switch-to-ground input pins.
9 – 15,
18 – 24
SG0 – 6,
SG13 – 7
Input Switch-to-Ground
Inputs 0 – 13
Switch-to-ground input pins.
16 VPWR Input Battery Input Battery supply input pin. Pin requires external reverse battery
protection.
17 WAKE Input/Output Wake-up Open drain wake-up output. Designed to control a power supply
enable pin.
29 INT Input/Output Interrupt Open-drain output to MCU. Used to indicate an input switch change of
state.
30 AMUX Output Analog Multiplex Output Analog multiplex output.
31 VDD Input Voltage Drain Supply 3.3 / 5.0 V supply. Sets SPI communication level for the SO driver.
32 SO Output SPI Slave Out Provides digital data from the 33972 to the MCU.
EP Ground Exposed Pad It is recommended that the exposed pad is terminated to GND (pin 1)
and system ground, however, the device will perform as specified with
the exposed pad unterminated (floating).
SO
1
SP7
SP6
SP5
SP4
SG7
SG8
SG9
SG10
SG11
SG13
WAKE
SG12
INT
VDD
AMUX
GND
SP0
SP1
SP2
SP3
SG0
SG1
SG2
SG3
SG4
SG6
VPWR
SG5
CS
SI
SCLK
8
9
10
11
12
13
14
15
16
3
4
5
6
7
2
32
25
24
23
22
21
20
19
18
17
30
29
28
27
26
31
Exposed Pad
EK Suffix
Only
SO
1
SP7
SP6
SP5
SP4
SG7
SG8
SG9
SG10
SG11
SG13
WAKE
SG12
INT
VDD
AMUX
GND
SP0
SP1
SP2
SP3
SG0
SG1
SG2
SG3
SG4
SG6
VPWR
SG5
CS
SI
SCLK
8
9
10
11
12
13
14
15
16
3
4
5
6
7
2
32
25
24
23
22
21
20
19
18
17
30
29
28
27
26
31
EW SuffixEK Suffix
Analog Integrated Circuit Device Data
Freescale Semiconductor 5
33972
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
Table 3. Maximum Ratings
All voltages are with respect to ground unless otherwise noted. Exceeding these ratings may cause a malfunction or
permanent damage to the device.
Ratings Symbol Value Unit
ELECTRICAL RATINGS
VDD Supply Voltage
CS, SI, SO, SCLK, INT, AMUX(1) –-0.3 to 7.0
VDC
WAKE(1) –-0.3 to 40 VDC
VPWR Supply Voltage(1) –-0.3 to 50 VDC
VPWR Supply Voltage at -40 °C(1) –-0.3 to 45 VDC
Switch Input Voltage Range –-14 to 40 VDC
Frequency of SPI Operation (VDD = 5.0 V) –6.0 MHz
ESD Voltage(3)
Human Body Model(2)
Applies to all non-input pins
Machine Model
Charge Device Model
Corner Pins
Interior Pins
VESD ±2000
±2000
±200
750
500
V
THERMAL RATINGS
Operating Temperature
Ambient
Junction
TA
TJ
- 40 to 125
- 40 to 150
°C
Storage Temperature TSTG - 55 to 150 °C
Power Dissipation (TA = 25 °C)(4) PD1.7 W
Thermal Resistance
Non-Exposed Pad
Junction to Ambient
Junction to Lead
Exposed Pad
Junction to Ambient
Junction to Exposed Pad
RθJA
RθJL
RθJA
RθJC
74
25
71
1.2
°C/W
Peak Package Reflow Temperature During Reflow(5), (6) TPPRT Note 6 °C
Notes
1. Exceeding these limits may cause malfunction or permanent damage to the device.
2. ESD data available upon request.
3. ESD1 testing is performed in accordance with the Human Body Model (CZAP = 100 pF, RZAP = 1500 Ω), and ESD2 testing is performed
in accordance with the Machine Model (CZAP = 200 pF, RZAP = 0 Ω).
4. Maximum power dissipation at TJ = 150°C junction temperature with no heat sink used.
5. Pin soldering temperature limit is for 10 seconds maximum duration. Not designed for immersion soldering. Exceeding these limits may
cause malfunction or permanent damage to the device.
6. Freescale’s Package Reflow capability meets Pb-free requirements for JEDEC standard J-STD-020C. For Peak Package Reflow
Temperature and Moisture Sensitivity Levels (MSL), Go to www.freescale.com, search by part number [e.g. remove prefixes/suffixes
and enter the core ID to view all orderable parts. (i.e. MC33xxxD enter 33xxx), and review parametrics.
Analog Integrated Circuit Device Data
6Freescale Semiconductor
33972
ELECTRICAL CHARACTERISTICS
STATIC ELECTRICAL CHARACTERISTICS
STATIC ELECTRICAL CHARACTERISTICS
Table 4. Static Electrical Characteristics
Characteristics noted under conditions 3.1 V ≤ VDD ≤ 5.25 V, 8.0 V ≤ VPWR ≤ 16 V, -40 °C ≤ TC ≤ 125 °C, unless otherwise
noted.(7) Where applicable, typical values reflect the parameter’s approximate average value with VPWR = 13 V, TA = 25 °C.
Characteristic Symbol Min Typ Max Unit
POWER INPUT
Supply Voltage
Supply Voltage Range Quasi-functional(8)
Fully Operational
Supply Voltage Range Quasi-functional(8)
VPWR
(QF)
VPWR
(FO)
VPWR
(QF)
5.5
8.0
26
–
–
–
8.0
26
38/40
V
Supply Current
All Switches Open, Normal Mode, Tri-state Disabled
IPWR
(ON)
–2.0 4.0
mA
Sleep State Supply Current
Scan Timer = 64 ms, Switches Open
IPWR
(SS)
40 70 100
μA
Logic Supply Voltage VDD 3.1 –5.25 V
Logic Supply Current
All Switches Open, Normal mode
IDD
–0.25 0.5
mA
Sleep State Logic Supply Current
Scan Timer = 64 ms, Switches Open
IDD(SS)
–10 20
μA
SWITCH INPUT
Pulse Wetting Current Switch-to-Battery (Current Sink) IPULSE 12 15 18 mA
Pulse Wetting Current Switch-to-Ground (Current Source) IPULSE 12 16 18 mA
Sustain Current Switch-to-Battery Input (Current Sink) ISUSTAIN 1.8 2.0 2.2 mA
Sustain Current Switch-to-Ground Input (Current Source) ISUSTAIN 1.8 2.0 2.2 mA
Sustain Current Matching Between Channels on Switch-to-Ground I/Os IMATCH
–2.0 4.0
%
Input Offset Current When Selected as Analog IOFFSET -2.0 1.4 2.0 μA
Input Offset Voltage When Selected as Analog
V(SP&SGINPUTS) to AMUX Output
VOFFSET
-10 2.5 10
mV
Analog Operational Amplifier Output Voltage
Sink 250 μA
VOL
–10 30
mV
Analog Operational Amplifier Output Voltage
Source 250 μA
VOH
VDD -0.1 – –
V
Switch Detection Threshold VTH 3.70 4.0 4.3 V
Switch Input Voltage Range
33972
33972A
VIN
-14
-14
–
–
38
40
V
Temperature Monitor(9), (10) TLIM 155 –185 °C
Temperature Monitor Hysteresis(10) TLIM(HYS) 5.0 10 15 °C
Notes
7. TC is the TCASE of the package
8. Device operational. Table parameters may be out of specification.
9. Thermal shutdown of 16 mA pull-up and pulldown current sources only. 2.0 mA current source / sink and all other functions remain active.
10. This parameter is guaranteed by design but is not production tested.
ISUS(MAX) -ISUS(MIN)
ISUS(MIN)
X 100
Analog Integrated Circuit Device Data
Freescale Semiconductor 7
33972
ELECTRICAL CHARACTERISTICS
STATIC ELECTRICAL CHARACTERISTICS
DIGITAL INTERFACE
Input Logic Voltage Thresholds(11) VINLOGIC 0.8 –2.2 V
SCLK, SI, Tri-state SO Input Current
0 V to VDD
ISCLK, ISI,
ISO (TRI) -10 –10
μA
CS Input Current
CS = VDD
ICS
-10 –10
μA
CS Pull-up Current
CS = 0 V
ICS
30 –100
μA
SO High-state Output Voltage
I
SO (HIGH) = -200 μA
VSO (HIGH)
VDD -0.8 – VDD
V
SO Low-state Output Voltage
I
SO (HIGH) = 1.6mA
VSO (LOW)
– – 0.4
V
Input Capacitance on SCLK, SI, Tri-state SO(12) CIN – – 20 pF
INT Internal Pull-up Current –15 40 100 μA
INT Voltage
INT = Open Circuit
V
INT (HIGH)
VDD -0.5 – VDD
V
INT Voltage
I INT = 1.0 mA
V
INT (LOW)
–0.2 0.4
V
WAKE Internal Pull-up Current I
WAKE
(PU) 20 40 100 μA
WAKE Voltage
WAKE = Open Circuit
V
WAKE
(HIGH)
4.0 4.3 5.3
V
WAKE Voltage
I
WAKE = 1.0 mA
V
WAKE(LOW)
–0.2 0.4
V
WAKE Voltage
Maximum Voltage Applied to WAKE Through External Pull-up
V
WAKE(MAX)
– – 40
V
Notes
11. Upper and lower logic threshold voltage levels apply to SI, CS, and SCLK.
12. This parameter is guaranteed by design but is not production tested.
Table 4. Static Electrical Characteristics (continued)
Characteristics noted under conditions 3.1 V ≤ VDD ≤ 5.25 V, 8.0 V ≤ VPWR ≤ 16 V, -40 °C ≤ TC ≤ 125 °C, unless otherwise
noted.(7) Where applicable, typical values reflect the parameter’s approximate average value with VPWR = 13 V, TA = 25 °C.
Characteristic Symbol Min Typ Max Unit
Analog Integrated Circuit Device Data
8Freescale Semiconductor
33972
ELECTRICAL CHARACTERISTICS
DYNAMIC ELECTRICAL CHARACTERISTICS
DYNAMIC ELECTRICAL CHARACTERISTICS
Table 5. Dynamic Electrical Characteristics
Characteristics noted under conditions 3.1 V ≤ VDD ≤ 5.25 V, 8.0 V ≤ VPWR ≤ 16 V, -40 °C ≤ TC ≤ 125 °C, unless otherwise
noted. Where applicable, typical values reflect the parameter’s approximate average value with VPWR = 13 V, TA = 25 °C.
Characteristic Symbol Min Typ Max Unit
SWITCH INPUT
Pulse Wetting Current Time t
PULSE (ON) 15 16 20 ms
Interrupt Delay Time
Normal Mode
t
INT-DLY
–5.0 16
μs
Sleep Mode Switch Scan Time t
SCAN 100 200 300 μs
Calibrated Scan Timer Accuracy
Sleep Mode
t SCAN TIMER
– – 10
%
Calibrated Interrupt Timer Accuracy
Sleep Mode
t INT TIMER
– – 10
%
DIGITAL INTERFACE TIMING(13)
Required Low-state Duration on VPWR for Reset(14)
VPWR ≤ 0.2 V
t
RESET
– – 10
μs
Falling Edge of CS to Rising Edge of SCLK
Required Set-up Time
t LEAD
100 – –
ns
Falling Edge of SCLK to Rising Edge of CS
Required Set-up Time
t LAG
50 – –
ns
SI to Falling Edge of SCLK
Required Set-up Time
t
SI (SU)
16 – –
ns
Falling Edge of SCLK to SI
Required Hold Time
t
SI (HOLD)
20 – –
ns
SI, CS, SCLK Signal Rise Time(15) t R
(SI) –5.0 –ns
SI, CS, SCLK Signal Fall Time(15) t F
(SI) –5.0 –ns
Time from Falling Edge of CS to SO Low-impedance(16) t
SO (EN) – – 55 ns
Time from Rising Edge of CS to SO High-impedance(17) t
SO (DIS) – – 55 ns
Time from Rising Edge of SCLK to SO Data Valid(18) t VALID –25 55 ns
Notes
13. These parameters are guaranteed by design. Production test equipment uses 4.16 MHz, 5.0 V SPI interface.
14. This parameter is guaranteed by design but not production tested.
15. Rise and Fall time of incoming SI, CS, and SCLK signals suggested for design consideration to prevent the occurrence of double pulsing.
16. Time required for valid output status data to be available on SO pin.
17. Time required for output states data to be terminated at SO pin.
18. Time required to obtain valid data out from SO following the rise of SCLK with 200 pF load.
Analog Integrated Circuit Device Data
Freescale Semiconductor 9
33972
ELECTRICAL CHARACTERISTICS
TIMING DIAGRAMS
TIMING DIAGRAMS
Figure 4. SPI Timing Characteristics
Figure 5. Sleep Mode to Normal Mode Operation
.
Figure 6. Normal Mode Interrupt Operation
tSO(DIS)
0.7 VDD
0.2 VDD
0.2 VDD
0.7 VDD
0.2 VDD
t
LEAD
tSO(EN)
tSI(SU) tSI(HOLD)
t
VALID
t
LAG
CS
SCLK
SI
SO
MSB IN
MSB OUT LSB OUT
0.7 VDD
0.2 VDD
VPWR
VDD
WAKE
INT
CS
SGn
Power-up Sleep Sleep Mode Normal
Mode
Sleep Command Sleep Mode Normal
Mode
Sleep Command
Wake-up From Interrupt
Timer Expire
Wake-up From
Closed Switch
Command
Normal Mode
Tri-state
Command
(Disable
Tri-state)
INT
CS
SGn Switch open ‚Äö
1
SGn Bit in SPI Word
Switch closed ‚Äö
1001
Switch
Command
0
on falling edge of CS
Latch switch status
Switch state change with
CS LOW generates INT
Switch state change with
CS LOW generates INT
Rising edge of CS does not
clear INT because state change
occurred while CS was LOW
Status Switch
Command
Status Switch
Command
Status Switch
Command
Status Switch
Command
Status Switch
Command
Status
Analog Integrated Circuit Device Data
10 Freescale Semiconductor
33972
FUNCTIONAL DESCRIPTION
INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
The 33972 device is an integrated circuit designed to
provide systems with ultra-low quiescent sleep / wake-up
modes, and a robust interface between switch contacts and
a microprocessor. The 33972 replaces many of the discrete
components required when interfacing to microprocessor-
based systems, while providing switch ground offset
protection, contact wetting current, and a system wake-up.
The 33972 features 8-programmable switch-to-ground or
switch-to-battery inputs and 14 switch-to-ground inputs. All
switch inputs may be read as analog inputs through the
analog multiplexer (AMUX). Other features include a
programmable wake-up timer, programmable interrupt timer,
programmable wake-up /interrupt bits, and programmable
wetting current settings.
This device is designed primarily for automotive
applications, but may be used in a variety of other
applications such as computer, telecommunications, and
industrial controls.
FUNCTIONAL PIN DESCRIPTION
CHIP SELECT (CS)
The system MCU selects the 33972 to receive
communication using the chip select (CS) pin. With the CS in
a logic LOW state, command words may be sent to the 33972
via the serial input (SI) pin, and switch status information can
be received by the MCU via the serial output (SO) pin. The
falling edge of CS enables the SO output, latches the state of
the INT pin, and the state of the external switch inputs.
Rising edge of the CS initiates the following operation:
1. Disables the SO driver (high-impedance)
2. INT pin is reset to logic [1], except when additional
switch changes occur during CS LOW. (See Figure 6
on page 9.)
3. Activates the received command word, allowing the
33972 to act upon new data from switch inputs.
To avoid any spurious data, it is essential the HIGH-to-
LOW and LOW-to-HIGH transitions of the CS signal occur
only when SCLK is in a logic LOW state. A clean CS is
needed to ensure no incomplete SPI words are sent to the
device. Internal to the 33972 device is an active pull-up to
VDD on CS.
In Sleep mode, the negative edge of CS (VDD applied) will
wake up the 33972 device. Data received from the device
during CS wake-up may not be accurate.
SYSTEM CLOCK (SCLK)
The system clock (SCLK) pin clocks the internal shift
register of the 33972. The SI data is latched into the input
shift register on the falling edge of SCLK signal. The SO pin
shifts the switch status bits out on the rising edge of SCLK.
The SO data is available for the MCU to read on the falling
edge of SCLK. False clocking of the shift register must be
avoided to ensure validity of data. It is essential the SCLK pin
be in a logic LOW state whenever CS makes any transition.
For this reason, it is recommended, that the SCLK pin is
commanded to a logic LOW state as long as the device is not
accessed and CS is in a logic HIGH state. When the CS is in
a logic HIGH state, any signal on the SCLK and SI pins will
be ignored and the SO pin is tri-state.
SPI SLAVE IN (SI)
The SI pin is used for serial instruction data input. SI
information is latched into the input register on the falling
edge of SCLK. A logic HIGH state present on SI will program
a one in the command word on the rising edge of the CS
signal. To program a complete word, 24 bits of information
must be entered into the device.
SPI SLAVE OUT (SO)
The SO pin is the output from the shift register. The SO pin
remains tri-stated until the CS pin transitions to a logic LOW
state. All open switches are reported as zero, all closed
switches are reported as one. The negative transition of CS
enables the SO driver.
The first positive transition of SCLK will make the status
data bit 24 available on the SO pin. Each successive positive
clock will make the next status data bit available for the MCU
to read on the falling edge of SCLK. The SI / SO shifting of the
data follows a first-in, first-out protocol, with both input and
output words transferring the most significant bit (MSB) first.
INTERRUPT (INT)
The INT pin is an interrupt output from the 33972 device.
The INT pin is an open-drain output with an internal pull-up to
VDD. In Normal mode, a switch state change will trigger the
INT pin (when enabled). The INT pin and INT bit in the SPI
register are latched on the falling edge of CS. This permits
the MCU to determine the origin of the interrupt. When two
33972 devices are used, only the device initiating the
interrupt will have the INT bit set. The INT pin is cleared on
the rising edge of CS. The INT pin will not clear with rising
edge of CS if a switch contact change has occurred while CS
was LOW.
In a multiple 33972 device system with WAKE HIGH and
VDD in (Sleep Mode), the falling edge of INT will place all
33972s in Normal mode.
Analog Integrated Circuit Device Data
Freescale Semiconductor 11
33972
FUNCTIONAL DESCRIPTION
FUNCTIONAL PIN DESCRIPTION
WAKE-UP (WAKE)
The WAKE pin is an open-drain output and a wake-up
input. The pin is designed to control a power supply Enable
pin. In the Normal mode, the WAKE pin is LOW. In the Sleep
mode, the WAKE pin is HIGH. The WAKE pin has a pull-up to
the internal + 5.0 V supply.
In Sleep mode with the WAKE pin HIGH, the falling edge
of WAKE will place the 33972 in Normal mode. In Sleep mode
with VDD applied, the INT pin must be HIGH for negative edge
of WAKE to wake up the device. If VDD is not applied to the
device in Sleep mode, INT does not affect WAKE operation.
BATTERY INPUT (VPWR)
The VPWR pin is battery input and Power-ON Reset to the
33972 IC. The VPWR pin requires external reverse battery
and transient protection. Maximum input voltage on VPWR is
50 V. All wetting, sustain, and internal logic current is
provided from the VPWR pin.
VOLTAGE DRAIN SUPPLY (VDD)
The VDD input pin is used to determine logic levels on the
microprocessor interface (SPI) pins. Current from VDD is
used to drive SO output and the pull-up current for CS and
INT pins. VDD must be applied for wake-up from negative
edge of CS or INT.
GROUND (GND)
The GND pin provides ground for the IC as well as ground
for inputs programmed as switch-to-battery inputs.
PROGRAMMABLE SWITCHES (SP0 : SP7)
The 33972 device has 8 switch inputs capable of being
programmed to read switch-to-ground or switch-to-battery
contacts. The input is compared with a 4.0 V reference.
When programmed to be switch-to-battery, voltages greater
than 4.0 V are considered closed. Voltages less than 4.0 V
are considered open. The opposite holds true when inputs
are programmed as switch-to-ground. Programming features
are defined in Table 6 through Table 11 in the Functional
Device Operation section of this datasheet beginning on
page 13. Voltages greater than the VPWR supply voltage will
source current through the SP inputs to the VPWR pin.
Transient battery voltages greater than 38/40 V must be
clamped by an external device. This is not a normal operating
condition and can damage the IC.
SWITCH-TO-GROUND INPUTS (SG0 : SG13)
The SGn pins are switch-to-ground inputs only. The input
is compared with a 4.0 V reference. Voltages greater than
4.0 V are considered open. Voltages less than 4.0 V are
considered closed. Programming features are defined in
Table 6 through Table 11 in the Functional Device Operation
section of this datasheet beginning on page 13. Voltages
greater than the VPWR supply voltage will source current
through the SG inputs to the VPWR pin. Transient battery
voltages greater than 40 V must be clamped by an external
device. This is not a normal operating condition and can
damage the IC.
Analog Integrated Circuit Device Data
12 Freescale Semiconductor
33972
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
Figure 7. Functional Internal Block Description
CONTROL AND PROTECTION CIRCUITRY:
The 33972 is designed to operate from 5.5 V to 38/40 V on
the VPWR terminal. Characteristics are provided for VPWR
from 8.0 to 26 V for the IC (parametric tests are done from 8.0
to 16.0v). Switch contact currents and the internal logic
supply are generated from the VPWR terminal. The VDD
supply terminal is used to set the SPI communication voltage
levels, current source for the SO driver, and pull-up current
on INT and CS.
The on-chip voltage regulator and bandgap supplies the
required voltages to the internal monitor circuitry. The
temperature monitor is active in the Normal mode.
INTERFACE AND CONTROL:
The 33972 Multiple Switch Detection Interface with
Suppressed Wake-up is designed to detect the closing and
opening of up to 22 switch contacts. The switch status, either
open or closed, is transferred to the microprocessor unit
(MCU) through a serial peripheral interface (SPI).
The device also features a 22-to-1 analog multiplexer for
reading inputs as analog. The 33972 device has two modes
of operation, Normal and Sleep.
SWITCH PROGRAMMABLE INPUTS:
Programmable switch detection inputs. These 8 inputs can
selectively detect switch closures to Ground or Battery. The
33972 device has 8 switch inputs capable of being
programmed to read switch-to-ground or switch-to-battery
contacts. The input is compared with a 4.0 V reference.
When programmed to be switch-to-battery, voltages greater
than 4.0 V are considered closed. Voltages less than 4.0 V
are considered open. The opposite holds true when inputs
are programmed as switch-to-ground.
SWITCH–TO-GROUND INPUTS:
Switch detection interface inputs. These 14 inputs can
detect switch closures to ground only. The input is compared
with a 4.0 V reference. Voltages greater than 4.0 V are
considered open. Voltages less than 4.0 V are considered
closed. Note: Each of these inputs may be used to supply
current to sensors external to a module.
MC33972 - Functional Block Diagram
Switch Programmable
Inputs
SP0 - SP7
Control & Protection
Voltage Regulation
Bandgap
Interface & Control
Multiplex Control
Control & Protection SW-GND InputsInterface & Control
Switch–to-Ground
Inputs
SG0 - SG13
Oscillator & Clock
Temp. Sense
Interrupt/Wake-up
SPI Interface
SW Prog Inputs
Analog Integrated Circuit Device Data
Freescale Semiconductor 13
33972
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
MCU INTERFACE DESCRIPTION
The 33972 device directly interfaces to a 3.3 or 5.0 V
microcontroller unit (MCU). SPI serial clock frequencies up to
6.0 MHz may be used for programming and reading switch
input status (production tested at 4.16 MHz). Figure 8
illustrates the configuration between an MCU and one 33972.
Serial peripheral interface (SPI) data is sent to the 33972
device through the SI input pin. As data is being clocked into
the SI pin, status information is being clocked out of the
device by the SO output pin. The response to a SPI
command will always return the switch status, interrupt flag,
and thermal flag. Input switch states are latched into the SO
register on the falling edge of the chip select (CS) pin.
Twenty-four bits are required to complete a transfer of
information between the 33972 and the MCU.
Figure 8. SPI Interface with Microprocessor
Two or more 33972 devices may be used in a module
system. Multiple ICs may be SPI-configured in parallel or
serial. Figures 9 and 10 show the configurations. When using
the serial configuration, 48-clock cycles are required to
transfer data in / out of the ICs.
Figure 9. SPI Parallel Interface with Microprocessor
Figure 10. SPI Serial Interface with Microprocessor
33972
MC68HCXX
Microcontroller
Receive
Buffer
Parallel
Ports
To Logic
24-Bit Shift RegisterShift Register
MOSI SI
MISO SO
SCLK
CS
INTINT
Parallel
Ports
MC68HCXX
Microcontroller 33972
33972
SI
SCLK
CS
INT
SI
SO
SCLK
CS
INT
INT
SCLK
MISO
MOSI
Shift Register
SO
Parallel
Ports
MC68HCXX
Microcontroller 33972
33972
SI
SCLK
CS
INT
SI
SO
SCLK
CS
INT
SO
INT
SCLK
MISO
MOSI
Shift Register
Analog Integrated Circuit Device Data
14 Freescale Semiconductor
33972
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
POWER SUPPLY
The 33972 is designed to operate from 5.5 to 40 V on the
VPWR pin. Characteristics are provided from 8.0 to 16 V for
the device. Switch contact currents and the internal logic
supply are generated from the VPWR pin. The VDD supply
pin is used to set the SPI communication voltage levels,
current source for the SO driver, and pull-up current on INT
and CS.
The VDD supply may be removed from the device to
reduce quiescent current. If VDD is removed while the device
is in Normal mode, the device will remain in Normal mode. If
VDD is removed in Sleep mode, the device will remain in
Sleep mode until a wake-up input is received (WAKE HIGH to
LOW, switch input or interrupt timer expires).
Removing VDD from the device disables SPI
communication and will not allow the device to wake up from
INT and CS pins.
POWER-ON RESET (POR)
Applying VPWR to the device will cause a Power-ON Reset
and place the device in Normal mode.
Default settings from Power-ON Reset via VPWR or the
Reset Command are as follows:
• Programmable switch – set to switch to battery
• All inputs set as wake-up
• Wetting current on (16 mA)
• Wetting current timer on (20 ms)
• All inputs tri-state
• Analog select 00000 (no input channel selected)
NORMAL AND SLEEP MODES
The 33972 has two operating modes, Normal mode and
Sleep mode. A discussion on Normal mode begins below.
A discussion on Sleep mode begins on page 19.
Normal Mode
Normal mode may be entered by the following events:
• Application of VPWR to the IC
• Change-of-switch state (when enabled)
• Falling edge of WAKE
• Falling edge of INT (with VDD = 5.0 V and WAKE at
Logic [1])
• Falling edge of CS (with VDD = 5.0 V)
• Interrupt timer expires
Only in Normal mode with VDD applied can the registers of
the 33972 be programmed through the SPI.
The registers that may be programmed in Normal mode
are listed below. Further explanation of each register is
provided in subsequent paragraphs.
•Programmable Switch Register (Settings Command )
•Wake-Up / Interrupt Register (Wake-up / Interrupt
Command )
•Wetting Current Register (Metallic Command )
•Wetting Current Timer Register (Wetting Current Timer
Enable Command )
•Tri-State Register (Tri-state Command )
•Analog Select Register (Analog Command )
•Calibration of Timers (Calibration Command )
•Reset (Reset Command )
Figure 6, page 9, is a graphical description of the device
operation in Normal mode. Switch states are latched into the
input register on the falling edge of CS. The INT to the MCU
is cleared on the rising edge of CS. However, INT will not
clear on rising edge of CS if a switch has closed during SPI
communication (CS LOW). This prevents switch states from
being missed by the MCU.
PROGRAMMABLE SWITCH REGISTER
Inputs SP0 to SP7 may be programmable for switch-to-
battery or switch-to-ground. These inputs types are defined
using the settings command (Table 6). To set an SPn input
for switch-to-battery, a logic [1] for the appropriate bit must be
set. To set an SPn input for switch-to-ground, a logic [0] for
the appropriate bit must be set. The MCU may change or
update the programmable switch register via software at any
time in Normal mode. Regardless of the setting, when the
SPn input switch is closed a logic [1] will be placed in the
serial output response register (Table 17, page 19).
WAKE-UP / INTERRUPT REGISTER
The wake-up / interrupt register defines the inputs that are
allowed to wake the 33972 from Sleep Mode or set the INT
pin LOW in Normal mode. Programming the wake-up /
interrupt bit to logic [0] will disable the specific input from
generating an interrupt and will disable the specific input from
waking the IC in Sleep mode (Table 7). Programming the
wake-up /interrupt bit to logic [1] will enable the specific input
to generate an interrupt with switch change of state and will
enable the specific input as wake-up. The MCU may change
or update the wake-up / interrupt register via software at any
time in Normal mode.
Table 6. Settings Command
Settings Command Not used Battery/Ground Select
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9876543210
0 0 0 0 0 0 0 1 X X X X X X X X sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0
Analog Integrated Circuit Device Data
Freescale Semiconductor 15
33972
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
WETTING CURRENT REGISTER
The 33972 has two levels of switch contact current, 16 and
2.0 mA (see Figure 11). The metallic command is used to set
the switch contact current level (Table 8). Programming the
metallic bit to logic [0] will set the switch wetting current to
2.0 mA. Programming the metallic bit to logic [1] will set the
switch contact wetting current to 16 mA. The MCU may
change or update the wetting current register via software at
any time in Normal mode.
Wetting current is designed to provide higher levels of
current during switch closure. The higher level of current is
designed to keep switch contacts from building up oxides that
form on the switch contact surface.
Figure 11. Contact Wetting and Sustain Current
WETTING CURRENT TIMER REGISTER
Each switch input has a designated 20 ms timer. The timer
starts when the specific switch input crosses the comparator
threshold (4.0 V). When the 20 ms timer expires, the contact
current is reduced from 16 to 2.0 mA. The wetting current
timer may be disabled for a specific input. When the timer is
disabled, 16 mA of current will continue to flow through the
closed switch contact. With multiple wetting current timers
disabled, power dissipation for the IC must be considered.
The MCU may change or update the wetting current timer
register via software at any time in Normal mode. This allows
the MCU to control the amount of time wetting current is
applied to the switch contact. Programming the wetting
current timer bit to logic [0] will disable the wetting current
timer. Programming the wetting current timer bit to logic [1]
will enable the wetting current timer (Table 9).
Table 7. Wake-up / Interrupt Command
Wake-up /Interrupt Command Command Bits
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9876543210
0 0 0 0 0 0 1 0 X X X X X X X X sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0
0 0 0 0 0 0 1 1 X X sg13 sg12 sg11 sg10 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0
Table 8. Metallic Command
Metallic Command Command Bits
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 0 0 0 0 1 0 0 X X X X X X X X sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0
0 0 0 0 0 1 0 1 X X sg13 sg12 sg11 sg10 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0
Table 9. Wetting Current Timer Enable Command
Wetting Current Timer Commands Command Bits
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 0 0 0 0 1 1 1 X X X X X X X X sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0
0 0 0 0 1 0 0 0 X X sg13 sg12 sg11 sg10 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0
Analog Integrated Circuit Device Data
16 Freescale Semiconductor
33972
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
TRI-STATE REGISTER
The tri-state command is use to set the SPn or SGn input
node as high-impedance (Table 10). By setting the tri-state
register bit to logic [1], the input will be high-impedance
regardless of the metallic command setting. The comparator
on each input remains active. This command allows the use
of each input as a comparator with a 4.0 V threshold. The
MCU may change or update the tri-state register via software
at any time in Normal mode.
ANALOG SELECT REGISTER
The analog voltage on switch inputs may be read by the
MCU using the analog command (Table 11). Internal to the
IC is a 22-to-1 analog multiplexer. The voltage present on the
selected input pin is buffered and made available on the
AMUX output pin. The AMUX output pin is clamped to a
maximum of VDD volts regardless of the higher voltages
present on the input pin. After an input has been selected as
the analog, the corresponding bit in the next SO data stream
will be logic [0]. When selecting a channel to be read as
analog, the user must also set the desired current (16 mA,
2.0 mA, or high-impedance). Setting bit 6 and bit 5 to 0,0
selects the input as high-impedance. Setting bit 6 and bit 5 to
0,1 selects 2.0 mA, and 1,0 selects 16 mA. Setting bit 6 and
bit 5 to 1,1 in the analog select register is not allowed and will
place the input as an analog input with high-impedance.
Analog currents set by the analog command are pull-up
currents for all SGn and SPn inputs (Table 11). The analog
command does not allow pull-down currents on the SPn
inputs. Setting the current to 16 or 2.0 mA may be useful for
reading sensor inputs. Further information is provided in the
Typical Applications section of this datasheet beginning on
page 21. The MCU may change or update the analog select
register via software at any time in Normal mode.
Table 10. Tri-State Command
Tri-State Commands Command Bits
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9876543210
0 0 0 0 1 0 0 1 X X X X X X X X sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0
0 0 0 0 1 0 1 0 X X sg13 sg12 sg11 sg10 sg9 sg8 sg7 sg6 sg5 sg4 sg3 sg2 sg1 sg0
Table 11. Analog Command
Analog Command Not used Current Select Analog Channel Select
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 0 0 0 0 1 1 0 X X X X X X X X X 16 mA 2.0 mA 0 0 0 0 0
Analog Integrated Circuit Device Data
Freescale Semiconductor 17
33972
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
CALIBRATION OF TIMERS
In cases where an accurate time base is required, the user
may calibrate the internal timers using the calibration
command (Table 13). After the 33972 device receives the
calibration command, the device expects 512 μs logic [0]
calibration pulse on the CS pin. The pulse is used to calibrate
the internal clock. No other SPI pins should transition during
this 512 μs calibration pulse. Because the oscillator
frequency changes with temperature, calibration is required
for an accurate time base. Calibrating the timers has no affect
on the quiescent current measurement. The calibration
command simply makes the time base more accurate. The
calibration command may be used to update the device on a
periodic basis.
Table 12. Analog Channel
Bits 43210 Analog Channel Select
00000 No Input Selected
00001 SG0
00010 SG1
00011 SG2
00100 SG3
00101 SG4
00110 SG5
00111 SG6
01000 SG7
01001 SG8
01010 SG9
01011 SG10
01100 SG11
01101 SG12
01110 SG13
01111 SP0
10000 SP1
10001 SP2
10010 SP3
10011 SP4
10100 SP5
10101 SP6
10110 SP7
Table 13. Calibration Command
Calibration Command Command Bits
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9876543210
00001011XXXXXXXXXXXXXXXX
Analog Integrated Circuit Device Data
18 Freescale Semiconductor
33972
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
RESET
The reset command resets all registers to Power-ON
Reset (POR) state. Refer to Table 15, page 18, for POR
states or the paragraph entitled Power-ON Reset (POR) on
page 14 of this datasheet.
SPI COMMAND SUMMARY
Table 15 below provides a comprehensive list of SPI
commands recognized by the 33972 and the reset state of
each register. Table 16 and Table 17 contain the serial
output (SO) data for input voltages greater or less than the
threshold level. Open switches are always indicated with a
logic [0], closed switches are indicated with logic [1].
Table 14. Reset Command
Reset Command Command Bits
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9876543210
01111111XXXXXXXXXXXXXXXX
Table 15. SPI Command Summary
MSB Command Bits Setting Bits LSBI
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Switch Status
Command 0 0 0 0 0 0 0 0 X X X X X X X X X X X X X X X X
Settings Command
Bat = 1, Gnd = 0
(Default state = 1)
0 0 0 0 0 0 0 1 X X X X X X X X SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0
Wake-Up/Interrupt Bit
Wake-Up = 1
Non-Wake-Up = 0
(Default state = 1)
0 0 0 0 0 0 1 0 X X X X X X X X SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0
0 0 0 0 0 0 1 1 X X SG13 SG12 SG11 SG10 SG9 SG8 SG7 SG6 SG5 SG4 SG3 SG2 SG1 SG0
Metallic Command
Metallic = 1
Non-metallic = 0
(Default state = 1)
0 0 0 0 0 1 0 0 X X X X X X X X SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0
0 0 0 0 0 1 0 1 X X SG13 SG12 SG11 SG10 SG9 SG8 SG7 SG6 SG5 SG4 SG3 SG2 SG1 SG0
Analog Command 0 0 0 0 0 1 1 0 X X X X X X X X X 16mA
0
2.0mA
00 0 0 0 0
Wetting Current Timer
Enable Command
Timer ON = 1
Timer OFF = 0
(Default state = 1)
0 0 0 0 0 1 1 1 X X X X X X X X SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0
0 0 0 0 1 0 0 0 X X SG13 SG12 SG11 SG10 SG9 SG8 SG7 SG6 SG5 SG4 SG3 SG2 SG1 SG0
Tri-State Command
Input Tri-State = 1
Input Active = 0
(Default state = 1)
0 0 0 0 1 0 0 1 X X X X X X X X SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0
0 0 0 0 1 0 1 0 X X SG13 SG12 SG11 SG10 SG9 SG8 SG7 SG6 SG5 SG4 SG3 SG2 SG1 SG0
Calibration Command
(Default state –
uncalibrated)
0 0 0 0 1 0 1 1 X X X X X X X X X X X X X X X X
Sleep Command
(Refer to Sleep Mode
on page 19.)
0 0 0 0 1 1 0 0 X X X X X X X X X X int
timer
int
timer
int
timer
scan
timer
scan
timer
scan
timer
Reset Command 0 1 1 1 1 1 1 1 X X X X X X X X X X X X X X X X
SO Response Will
Always Send
them
flg
int
flg SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SG13 SG12 SG11 SG10 SG9 SG8 SG7 SG6 SG5 SG4 SG3 SG2 SG1 SG0
Analog Integrated Circuit Device Data
Freescale Semiconductor 19
33972
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
EXAMPLE OF NORMAL MODE OPERATION
The operation of the device in Normal mode is defined by
the states of the programmable internal control registers. A
typical application may have the following settings:
• Programmable switch – set to switch-to-ground
• All inputs set as wake-up
• Wetting current on (16 mA)
• Wetting current timer on (20 ms)
• All inputs tri-state-disabled (comparator is active)
• Analog select 00000 (no input channel selected)
With the device programmed as above, an interrupt will be
generated with each switch contact change of state (open-to-
close or close-to-open) and 16 mA of contact wetting current
will be source for 20 ms. The INT pin will remain LOW until
switch status is acknowledged by the microprocessor. It is
critical to understand INT will not be cleared on the rising
edge of CS if a switch closure occurs while CS is LOW. The
maximum duration a switch state change can exist without
acknowledgement depends on the software response time to
the interrupt. Figure 6, page 9, shows the interaction
between changing input states and the INT and CS pins.
If desired the user may disable interrupts (wake up/
interrupt command) from the 33972 device and read the
switch states on a periodic basis. Switch activation and
deactivation faster than the MCU read rate will not be
acknowledged.
The 33972 device will exit the Normal mode and enter the
Sleep mode only with a valid sleep command.
SLEEP MODE
Sleep mode is used to reduce system quiescent currents.
Sleep mode may be entered only by sending the sleep
command. All register settings programmed in Normal mode
will be maintained in Sleep mode.
The 33972 will exit Sleep mode and enter Normal mode
when any of the following events occur:
• Input switch change of state (when enabled)
• Interrupt timer expire
• Falling edge of WAKE
• Falling edge of INT (with VDD = 5.0 V and WAKE at
Logic [1])
• Falling edge of CS (with VDD = 5.0 V)
• Power-ON Reset (POR)
The VDD supply may be removed from the device during
Sleep mode. However removing VDD from the device in Sleep
mode will disable a wake-up from falling edge of INT and CS.
Note In cases where CS is used to wake the device, the
first SO data message is not valid.
The sleep command contains settings for two
programmable timers for Sleep mode, the interrupt timer and
the scan timer, as shown in Table 18 The interrupt timer is
used as a periodic wake-up timer. When the timer expires, an
interrupt is generated and the device enters Normal mode.
Note The interrupt timer in the 33972 device may be
disabled by programming the interrupt bits to logic [1 1 1].
Table 19 shows the programmable settings of the Interrupt
timer.
Table 16. Serial Output (SO) Bit Data
Type of Input Input
Programmed
Voltage on
Input Pin SO SPI Bit
SP Switch to Ground SPn < 4.0V 1
Switch to Ground SPn > 4.0V 0
Switch to Battery SPn < 4.0V 0
Switch to Battery SPn > 4.0V 1
SG N/A SGn < 4.0V 1
N/A SGn > 4.0V 0
Table 17. Serial Output (SO) Response Register
SO Response Will
Always Send
them
flg
int
flg SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SG13 SG12 SG11 SG10 SG9 SG8 SG7 SG6 SG5 SG4 SG3 SG2 SG1 SG0
Table 18. Sleep Command
Sleep Command Command Bits
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9876543210
0 0 0 0 1 1 0 0 X X X X X X X X X X
int timer
int timer
int timer
scan timer
scan timer
scan timer
Analog Integrated Circuit Device Data
20 Freescale Semiconductor
33972
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
The scan timer sets the polling period between input
switch reads in Sleep mode. The period is set in the sleep
command and may be set to 000 (no period) to 111 (64 ms).
In Sleep mode when the scan timer expires, inputs will
behave as programmed prior to sleep command. The 33972
will wake up for approximately 125 μs and read the switch
inputs. At the end of the 125 μs, the input switch states are
compared with the switch state prior to sleep command.
When switch state changes are detected, an interrupt is
generated (when enabled; refer to wake-up / interrupt
command description on page 15), and the device enters
Normal mode. Without switch state changes, the 33972 will
reset the scan timer, inputs become tri-state, and the Sleep
mode continues until the scan timer expires again.
Table 20 shows the programmable settings of the Scan
timer.
Note The interrupt and scan timers are disabled in the
Normal Mode.
Figure 5, page 9, is a graphical description of how the
33972 device exits Sleep mode and enters Normal mode.
Notice that the device will exit Sleep mode when the interrupt
timer expires or when a switch change of state occurs. The
falling edge of INT triggers the MCU to wake from Sleep
state. Figure 12 illustrates the current consumed during
Sleep mode. During the 125 μs, the device is fully active and
switch states are read. The quiescent current is calculated by
integrating the normal running current over scan period plus
approximately 60 μA.
Figure 12. Sleep Current Waveform
TEMPERATURE MONITOR
With multiple switch inputs closed and the device
programmed with the wetting current timers disabled,
considerable power will be dissipated by the IC. For this
reason, temperature monitoring has been implemented. The
temperature monitor is active in the Normal mode only. When
the IC temperature is above the thermal limit, the temperature
monitor will do all of the following:
• Generate an interrupt.
• Force all 16 mA pull-up and pull-down current sources
to revert to 2.0 mA current sources.
• Maintain the 2.0 mA current source and all other
functionality.
• Set the thermal flag bit in the SPI output register.
The thermal flag bit in the SPI word will be cleared on rising
edge of CS provided the die temperature has cooled below
the thermal limit. When die temperature has cooled below
thermal limit, the device will resume previously programmed
settings.
Table 19. Interrupt Timer
Bits 543 Interrupt Period
000 32 ms
001 64 ms
010 128 ms
011 256 ms
100 512 ms
101 1.024 s
110 2.048 s
111 No interrupt wake-up
Table 20. Scan Timer
Bits 210 Scan Period
000 No Scan
001 1.0 ms
010 2.0 ms
011 4.0 ms
100 8.0 ms
101 16 ms
110 32 ms
111 64 ms
Inputs active for 125 us
out of 32 ms
I=V/R or 0.270V/100ohm = 2.7mA
I=V/R or 6mV/100ohm = 60 uA
Inputs active for 125 us
out of 32 ms
I=V/R or 0.270V/100ohm = 2.7mA
I=V/R or 6mV/100ohm = 60 uA
Inputs active for 125 us
out of 32 ms
I=V/R or 0.270V/100ohm = 2.7mA
I=V/R or 6mV/100ohm = 60 uA
I = V/R or 0.270V/100Ω = 2.7mA
Inputs active for
125μs out of 32ms I = V/R or
6.0mV/100Ω = 60μA
Analog Integrated Circuit Device Data
Freescale Semiconductor 21
33972
TYPICAL APPLICATIONS
INTRODUCTION
TYPICAL APPLICATIONS
INTRODUCTION
The 33972’s primary function is the detection of open or
closed switch contacts. However, there are many features
that allow the device to be used in a variety of applications.
The following is a list of applications to consider for the IC:
Sensor Power Supply
Switch Monitor for Metallic or Elastomeric Switches
Analog Sensor Inputs (Ratiometric)
Power MOSFET / LED Driver and Monitor
Multiple 33972 Devices in a Module System
The following paragraphs describe the applications in
detail.
SENSOR POWER SUPPLY
Each input may be used to supply current to sensors
external to a module. Many sensors such as Hall effect,
pressure sensors, and temperature sensors require a supply
voltage to power the sensor and provide an open collector or
analog output. Figure 13 shows how the 33972 may be used
to supply power and interface to these types of sensors. In an
application where the input makes continuous transitions,
consider using the wake-up / interrupt command to disable
the interrupt for the particular input.
Figure 13. Sensor Power Supply
METALLIC / ELASTOMERIC SWITCH
Metallic switch contacts often develop higher contact
resistance over time owing to contact corrosion. The
corrosion is induced by humidity, salt, and other elements
that exist in the environment. For this reason the 33972
provides two settings for contacts. When programmed for
metallic switches, the device provides higher wetting current
to keep switch contacts free of oxides. The higher current
occurs for the first 20 ms of switch closure. Where longer
duration of wetting current is desired, the user may send the
wetting current timer command and disable the timer. Wetting
current will be continuous to the closed switch. After the time
period set by the MCU, the wetting current timer command
may be sent again to enable the timer. The user must
consider power dissipation on the device when disabling the
timer. (Refer to the paragraph entitled Temperature Monitor,
page 20.)
To increase the amount of wetting current for a switch
contact, the user has two options. Higher wetting current to a
switch may be achieved by paralleling SGn or SPn inputs.
This will increase wetting current by 16 mA for each input
added to the switch contact. The second option is to simply
add an external resistor pull-up to the VPWR supply for switch-
to-ground inputs or a resistor to ground for a switch-to-battery
input. Adding an external resistor has no effect on the
operation of the device.
Elastomeric switch contacts are made of carbon and have
a high contact resistance. Resistance of 1.0 kΩ is common.
In applications with elastomeric switches, the pull-up and
pulldown currents must be reduced to prevent excessive
power dissipation at the contact. Programming for a lower
current settings is provided in the Functional Device
Operation section beginning on page 13 under Table 8,
Metallic Command.
ANALOG SENSOR INPUTS (RATIOMETRIC)
The 33972 features a 22-to-1 analog multiplexer. Setting
the binary code for a specific input in the analog command
allows the microcontroller to perform analog to digital
conversion on any of the 22 inputs. On rising edge of CS the
multiplexer connects a requested input to the AMUX pin. The
AMUX pin is clamped to max of VDD volts regardless of the
higher voltages present on the input pin. After an input has
been selected as the analog, the corresponding bit in the next
SO data stream will be logic [0].
The input pin, when selected as analog, may be
configured as analog with high-impedance, analog with
2.0 mA pull-up, or analog with 16 mA pull-up. Figure 14,
page 22, shows how the 33972 may be used to provide a
ratiometric reading of variable resistive input.
VDD
VPWR
V
DD
SI
SO
SCLK
INT
CS
MOSI
MISO
V
BAT
SP0
SP1
SP7
SG1
SG0
SG12
SG13
WAKE
33972
SCLK
CS
INT
MCU
16 2.0
V
PWR
V
PWR
16 mA
IOC[7:0]
X
Reg
Input Capture
Timer Port
Hall-Effect
Sensor
2.5 k
Ω
mA
16 2.0
V
PWR
V
PWR
mA
2.5 k
Ω
V
BAT
mA
mA
Analog Integrated Circuit Device Data
22 Freescale Semiconductor
33972
TYPICAL APPLICATIONS
INTRODUCTION
Figure 14. Analog Ratiometric Conversion
To read a potentiometer sensor, the wiper should be
grounded and brought back to the module ground, as
illustrated in Figure 14. With the wiper changing the
impedance of the sensor, the analog voltage on the input will
represent the position of the sensor.
Using the Analog feature to provide 2.0 mA of pull-up
current to an analog sensor may induce error due to the
accuracy of the current source. For this reason, a ratiometric
conversion must be considered. Using two current sources
(one for the sensor and one to set the reference voltage to the
A / D converter) will yield a maximum error (owing to the
33972) of 4%.
Higher accuracy may be achieved through module level
calibration. In this example, we use the resistor values from
Figure 14 and assume the current sources are 4% from each
other. The user may use the module end-of-line tester to
calculate the error in the A / D conversion. By placing a
2.0 kΩ, 0.1% resistor in the end-of-line test equipment and
assuming a perfect 2.0 mA current source from the 33972, a
calculated A / D conversion may be obtained. Using the
equation yields the following:
The ADC value of 213 counts is the value with 0% error
(neglecting the resistor tolerance and AMUX input offset
voltage). Now we can calculate the count value induced by
the mismatch in current sources. From a sample device the
maximum current source was measured at 2.05 mA and
minimum current source was measured at 1.99 mA. This
yields 3% error in A / D conversion. The A / D measurement
will be as follows:
This A / D conversion is 3% low in value. The error
correction factor of 1.03 may be used to correct the value:
An error correction factor may then be stored in E2
memory and used in the A / D calculation for the specific input.
Each input used as analog measurement will have a
dedicated calibrated error correction factor.
POWER MOSFET / LED DRIVER AND MONITOR
Because of the flexible programming of the 33972 device,
it may be used to drive small loads like LEDs or MOSFET
gates. It was specifically designed to power up in the Normal
mode with the inputs tri-state. This was done to ensure the
LEDs or MOSFETs connected to the 33972 power up in the
off-state. The switch programmable inputs (SP0 – SP7) have
a source-and-sink capability, providing effective MOSFET
gate control. To complete the circuit, a pull-down resistor
should be used to keep the gate from floating during the
Sleep modes. Figure 15, page 23, shows an application
where the SG0 input is used to monitor the drain-to-source
voltage of the external MOSFET. The 1.5 kΩ resistor is used
to set the drain-to-source trip voltage. With the 2.0 mA
current source enabled, an interrupt will be generated when
the drain-to-source voltage is approximately 1.0 V.
VDD
VPWR
V
DD
SI
SO
SCLK
INT
CS
AMUX
MOSI
MISO
AN0
V
BAT
SP0
SP1
SP7
SG1
SG0
SG12
SG13
WAKE
V
BAT
SCLK
CS
INT
16 2.0
V
PWR
2.0mA
2.0mA
2.39k
Ω
0.1%
4.54V to 5.02V
Analog
Ports
V
REF(H)
V
REF(L)
Analog Sensor
or Analog Switch
R
2
I
2
I
1
R
1
V
PWR
mA
2.0
V
PWR
V
PWR
mA
16
mA
mA
33972
MCU
ADC = I1 x R1
I2 x R2 x 255
ADC = 2.0mA x 2.0kΩx 255
2.0mA x 2.39kΩ
ADC = 213 counts
ADC = 1.99mA x 2.0kΩx255
2.05mA x 2.39kΩ
ADC = 207 counts
ADC = 207 counts x 1.03
ADC = 213 counts
Analog Integrated Circuit Device Data
Freescale Semiconductor 23
33972
TYPICAL APPLICATIONS
INTRODUCTION
Figure 15. MOSFET or LED Driver Output
The sequence of commands (from Normal mode with
inputs tri-state) required to set up the device to drive a
MOSFET are as follows:
• wetting current timer enable command – Disable SPn
wetting current timer (refer to Table 9, page 15).
• metallic command – Set SPn to 16 or 2.0 mA gate drive
current (refer to Table 8, page 15).
• settings command – Set SPn as switch-to-battery (refer
to Table 6, page 14).
• tri-state command – Disable tri-state for SPn (refer to
Table 10, page 16).
After the tri-state command has been sent (tri-state
disable), the MOSFET gate will be pulled to ground. From this
point forward the MOSFET may be turned on and off by
sending the settings command :
• settings command – SPn as switch-to-ground
(MOSFET ON).
• settings command – SPn as switch-to-battery
(MOSFET OFF).
Monitoring of the MOSFET drain in the OFF state provides
open load detection. This is done by using an SGn input
comparator. With the SGn input in tri-state, the load will pull
up the SGn input to battery. With open load the SGn pin is
pulled down to ground through an external resistor. The open
load is indicated by a logic [1] in the SO data bit.
The analog command may be used to monitor the drain
voltage in the MOSFET ON state. By sourcing 2.0 mA of
current to the 1.5 kΩ resistor, the analog voltage on the SGn
pin will be approximately:
As the voltage on the drain of the MOSFET increases, so
does the voltage on the SGn pin. With the SGn pin selected
as analog, the MCU may perform the A / D conversion.
Using this method for controlling unclamped inductive
loads is not recommended. Inductive flyback voltages greater
than VPWR may damage the IC.
The SP0 : SP7 pins of this device may also be used to send
signals from one module to another. Operation is similar to
the gate control of a MOSFET.
• For LED applications a resistor in series with the LED is
recommended but not required. The switch-to-ground
inputs are recommended for LED application. To drive
the LED use the following commands:
• wetting current timer enable command – Disable SGn
wetting current timer.
• metallic command – Set SGn to 16 mA.
From this point forward the LED may be turned on and off
using the tri-state command :
• tri-state command – Disable tri-state for SGn (LED ON).
• tri-state command – Enable tri-state for SGn (LED
OFF).
These parameters are easily programmed via SPI
commands in Normal mode.
MULTIPLE 33972 DEVICES IN A MODULE SYSTEM
Connecting power to the 33972 and the MCU for Sleep
mode operation may be done in several ways. Table 21
shows several system configurations for power between the
MCU and the 33972 and their specific requirements for
functionality.
Multiple 33972 devices may be used in a module system.
SPI control may be done in parallel or serial. However when
parallel mode is used, each device is addressed
independently (refer to MCU Interface Description, page 13).
Therefore when sending the sleep command, one device will
enter sleep before the other. For multiple devices in a system,
it is recommended that the devices are controlled in serial (S0
SP0
SG0
SG13
16 2.0
4.0V Ref +
-
Comparator
To SPI
VPWR SG0
1.5kΩ
LOAD
VBAT
AMUX
100kΩ
mA
VPWR
+
-
Comparator
To SPI
4.0V
Ref
2.0
2.0mA
16
mA
16
mA
VPWR
VPWR SG0
16 2.0
VPWR
mA
VPWR
+
Comparator
To SPI
4.0V Ref
SG13
-
mA
mA
mA
Table 21. Sleep Mode Power Supply
MCU
VDD
33972
VDD
Comments
5.0 V 5.0 V All wake-up conditions apply. (Refer to Sleep
Mode, page 19.)
5.0 V 0 V SPI wake-up is not possible.
0 V 5.0 V Sleep mode not possible. Current from CS pull-
up will flow through MCU to VDD that has been
switched off. Negative edge of CS will put
33972 in Normal mode.
0 V 0 V SPI wake-up is not possible.
VSGn = ISGn x 1.5kΩ + VDS
Analog Integrated Circuit Device Data
24 Freescale Semiconductor
33972
TYPICAL APPLICATIONS
INTRODUCTION
from first device is connected to SI of second device). With
two devices, 48 clock pulses are required to shift data in.
When the WAKE feature is used to enable the power supply,
both WAKE pins should be connected to the enable pin on the
power supply. The INT pins may be connected to one
interrupt pin on the MCU or may have their own dedicated
interrupt to the MCU.
The transition from Normal to Sleep mode is done by
sending the sleep command. With the devices connected in
serial and the sleep command sent, both will enter Sleep
mode on the rising edge of CS. When Sleep mode is entered,
the WAKE pin will be logic [1]. If either device wakes up, the
WAKE pin will transition LOW, waking the other device.
A condition exists where the MCU is sending the sleep
command (CS logic [0]) and a switch input changes state.
With this event the device that detects this input will not
transition to Sleep mode, while the second device will enter
Sleep mode. In this case two switch status commands must
be sent to receive accurate switch status data. The first
switch status command will wake the device in Sleep mode.
Switch status data may not be valid from the first switch
status command because of the time required for the input
voltage to rise above the 4.0 V input comparator threshold.
This time is dependant on the impedance of SGn or SPn
node. The second switch status command will provide
accurate switch status information. It is recommended that
software wait 10 to 20 ms between the two switch status
commands, allowing time for switch input voltages to
stabilize. With all switch states acknowledged by the MCU,
the sleep sequence may be initiated. All parameters for Sleep
mode should be updated prior to sending the sleep
command.
The 33972 IC has an internal 5.0 V supply from the VPWR
pin. A POR circuit monitors the internal 5.0 V supply. In the
event of transients on the VPWR pin, an internal reset may
occur. Upon reset the 33972 will enter Normal mode with the
internal registers as defined in Table 15, page 18. Therefore
it is recommended that the MCU periodically update all
registers internal to the IC.
USING THE WAKE FEATURE
The 33972 provides a WAKE output and wake-up input
designed to control an enable pin on system power supply.
While in the Normal mode, the WAKE output is LOW,
enabling the power supply. In the Sleep mode, the WAKE pin
is high, disabling the power supply. The WAKE pin has a
passive pull-up to the internal 5.0 V supply but may be pulled
up through a resistor to the VPWR supply (see Figure 17,
page 25)
When the WAKE output is not used, the pin should be
pulled up to the VDD supply through a resistor as shown in
Figure 16, page 25.
During the Sleep mode, a switch closure will set the WAKE
pin LOW, causing the 33972 to enter the Normal mode. The
power supply will then be activated, supplying power to the
VDD pin and the microprocessor and the 33972. The
microprocessor can determine the source of the wake-up by
reading the interrupt flag.
COST AND FLEXIBILITY
Systems requiring a significant number of switch
interfaces have many discrete components. Discrete
components on standard PWB consume board space and
must be checked for solder joint integrity. An integrated
approach reduces solder joints, consumes less board space,
and offers wider operating voltage, analog interface
capability, and greater interfacing flexibility.
Analog Integrated Circuit Device Data
Freescale Semiconductor 25
33972
TYPICAL APPLICATIONS
INTRODUCTION
Figure 16. Power Supply Active in Sleep Mode
Figure 17. Power Supply Shutdown in Sleep Mode
VDD
MC68HCXX
Microprocessor
33972
VBAT Power
MOSI
MISO
AN0
WAKE
SI
SO
SCLK
INT
CS
AMUX
V
BAT
V
BAT
SP0
SP1
SP7
SG1
SG0
SG12
SG13
Supply
VDD
SCLK
INT
CS
VPWR
VPWR
VDD
VDD
GND
EP
MC68HCXX
Microprocessor
33972
VBAT Power
MOSI
MISO
AN0
WAKE
SI
SO
SCLK
INT
CS
AMUX
V
BAT
V
BAT
SP0
SP1
SP7
SG1
SG0
SG12
SG13
Supply
VDD
SCLK
INT
CS
Enable
VPWR
VDD
VDD
VDD
VPWR
GND
EP
Analog Integrated Circuit Device Data
26 Freescale Semiconductor
33972
PACKAGING
PACKAGE DIMENSIONS
PACKAGING
PACKAGE DIMENSIONS
For the most current package revision, visit www.freescale.com and perform a keyword search using the 98A listed below.
EW SUFFIX (Pb-FREE)
32-LEAD SOIC WIDE BODY
98ARH99137A
ISSUE B
Analog Integrated Circuit Device Data
Freescale Semiconductor 27
33972
PACKAGING
PACKAGE DIMENSIONS (CONTINUED)
PACKAGE DIMENSIONS (CONTINUED)
EW SUFFIX (Pb-FREE)
32-LEAD SOIC WIDE BODY
98ARH99137A
ISSUE B
Analog Integrated Circuit Device Data
28 Freescale Semiconductor
33972
PACKAGING
PACKAGE DIMENSIONS (CONTINUED)
EK SUFFIX (Pb-FREE)
32-LEAD SOIC WIDE BODY
EXPOSED PAD
98ASA10556D
ISSUE D
Analog Integrated Circuit Device Data
Freescale Semiconductor 29
33972
PACKAGING
PACKAGE DIMENSIONS (CONTINUED)
EK SUFFIX (Pb-FREE)
32-LEAD SOIC WIDE BODY
EXPOSED PAD
98ASA10556D
ISSUE D
Analog Integrated Circuit Device Data
30 Freescale Semiconductor
33972
PACKAGING
PACKAGE DIMENSIONS (CONTINUED)
EK SUFFIX (Pb-FREE)
32-LEAD SOIC WIDE BODY
EXPOSED PAD
98ASA10556D
ISSUE D
Analog Integrated Circuit Device Data
Freescale Semiconductor 31
33972
REVISION HISTORY
REVISION HISTORY
REVISION DATE DESCRIPTION OF CHANGES
4.0 2/2006 • Converted to Freescale format
• Added PC33972A version
• Changed Figure 15, Power Supply Active in Sleep Mode
• Changed Figure 16, Power Supply Shutdown in Sleep Mode
• Updated Outline Drawing for package
5.0 6/2006 • Update to the prevailing Freescale form and style.
6.0 7/2006 • Added MC33972T devices.
• Updated StatiC Electrical Characteristics on page 6 with 33972T parameters.
7.0 11/2006 • Changed Human Body Model parameters in Maximum Ratings table.
• Replaced Part Number MC33972TEW/R2 with MCZ33972TEW/R2
• Removed Peak Package Reflow Temperature During Reflow (solder reflow) parameter from
Maximum Ratings on page 5. Added note with instructions to obtain this information from
www.freescale.com.
8.0 12/2006 • Restated note (6)
• Changed Part Number MCZ33972TEW/R2 with MC33972TEW/R2
9.0 4/2007 • Removed all references to the 33972T device.
• Removed the MC33972TDWB/R2, MC33972TEW/R2, and PC33972AEW/R2 from the ordering
information.
• Added MCZ33972AEW/R2 to the ordering information.
10.0 6/2007 • Added MC33972EW/R2, MC33972TDWB/R2, MC33972TEW/R2, and MCZ33972TEW/R2 to the
ordering information.
11.0 11/2007 • Updated to the current Freescale form and style
• Added MC33972AEK/R2 to the ordering information.
• Included device specific information relevant to the EK suffix on pages 1, 2, 4, 5, 6, 27, and 28.
• Added sentence to CHIP SELECT (CS) on page 10
• Made calculation corrections to Analog Sensor Inputs (Ratiometric)
12.0 12/2007 • Corrected Device Variation Table on page 2.
13.0 12/2007 • Replaced Outline Drawing 98ARL10543D with 98ASA10556D.
14.0 6/2008 • Added Note 7, “TC is the TCASE of the package” to Electrical Characteristics Table.
15.0 8/2008 • Updated package drawing 98ASA10556D
16.0 10/2009 • Updated data sheet status from Advance Information to Technical Data
• Updated to the current Freescale form and style
17.0 2/2011 • Updated Freescale form and style
• Added RoHS symbol
18.0 8/2011 • Revised Ordering Information Table by adding part numbers MC33972AEK/R2 and
MC33972ATEW/R2, and removing part numbers MC33972DWB/R2 and MC33972TDWB/R2.
19.0 3/2012 • Added the sentence “This condition in not a normal operating condition and can cause damage to
the IC.” to Programmable Switches (SP0 : SP7) and Switch-to-ground Inputs (SG0 : SG13)
• Changed sentence in Control and Protection Circuitry: “Characteristics are provided for VPWR from
8.0v to 26v for the IC (parametric tests are done from 8.0v to 16.0v).”
Document Number: MC33972
Rev. 19.0
3/2012
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