For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.
__________________General Description
The MAX1242/MAX1243 are low-power, 10-bit analog-
to-digital converters (ADCs) available in 8-pin pack-
ages. They operate with a single +2.7V to +5.25V
supply and feature a 7.5µs successive-approximation
ADC, a fast track/hold (1.5µs), an on-chip clock, and a
high-speed, 3-wire serial interface.
Power consumption is only 3mW (VDD = 3V) at the
73ksps maximum sampling speed. A 2µA shutdown
mode reduces power at slower throughput rates.
The MAX1242 has an internal 2.5V reference, while the
MAX1243 requires an external reference. The MAX1243
accepts signals from 0V to VREF, and the reference
input range includes the positive supply rail. An exter-
nal clock accesses data from the 3-wire interface,
which connects directly to standard microcontroller I/O
ports. The interface is compatible with SPI™, QSPI™,
and Microwire™.
Excellent AC characteristics and very low power com-
bined with ease of use and small package size make
these converters ideal for remote-sensor and data-
acquisition applications, or for other circuits with
demanding power consumption and space require-
ments. The MAX1242/MAX1243 are available in 8-pin
DIP and SO packages.
Applications
Portable Data Logging Process Control Monitoring
Test Equipment Temperature Measurement
Isolated Data Acquisition
________________________________Features
♦+2.7V to +5.25V Single-Supply Operation
♦10-Bit Resolution
♦Internal 2.5V Reference (MAX1242)
♦Small Footprint: 8-Pin DIP and SO Packages
♦Low Power: 3.7mW (73ksps, MAX1242)
3mW (73ksps, MAX1243)
66µW (1ksps, MAX1243)
5µW (power-down mode)
♦Internal Track/Hold
♦SPI™/QSPI™/Microwire™ 3-Wire Serial Interface
♦Pin-Compatible 12-Bit Upgrades:
MAX1240/MAX1241
MAX1242/MAX1243
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
________________________________________________________________
Maxim Integrated Products
1
19-1156; Rev 2; 6/98
SPI and QSPI are trademarks of Motorola, Inc. Microwire is a trademark of National Semiconductor Corp.
Ordering Information continued at end of data sheet.
Note:
Order the MAX1242A in place of the MAX1242C. Order the
MAX1242B in place of the MAX1242D.
________________Functional Diagram
7
AIN T/H
DOUT
6
1
5
OUTPUT
SHIFT
REGISTER
CONTROL
LOGIC
2.5V
REFERENCE
MAX1242 ONLY
INT
CLOCK
10-BIT
SAR
8
2
3
REF 4
SHDN
SCLK
CS
MAX1242
MAX1243
VDD
GND
TOP VIEW
1
2
3
4
8
7
6
5
SCLK
CS
DOUT
GND
REF
SHDN
AIN
VDD
DIP/SO
MAX1242
MAX1243
Pin Configuration
_________________Ordering Information
±18 Plastic DIP-40°C to +85°CMAX1242BEPA ±1/28 Plastic DIP-40°C to +85°CMAX1242AEPA
±1/28 SO0°C to +70°CMAX1242ACSA ±1
±1
±1/2
INL
(LSB)
8 SO
8 Plastic DIP
8 Plastic DIP
PIN-
PACKAGE
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°CMAX1242BCSA
MAX1242BCPA
MAX1242ACPA
PART
Gain Temperature Coefficient
MAX1242/MAX1243
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
2 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS
(VDD = +2.7V to +5.25V; 73ksps; fSCLK = 2.1MHz (50% duty cycle); MAX1242—4.7µF capacitor at REF pin, MAX1243—external
reference; VREF = 2.5V applied to REF pin; TA= TMIN to TMAX; unless otherwise noted.)
VDD to GND.............................................................-0.3V to +6V
AIN to GND................................................-0.3V to (VDD + 0.3V)
REF to GND...............................................-0.3V to (VDD + 0.3V)
Digital Inputs to GND...............................................-0.3V to +6V
DOUT to GND............................................-0.3V to (VDD + 0.3V)
DOUT Current..................................................................±25mA
Continuous Power Dissipation (TA = +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C)...........727mW
SO (derate 5.88mW/°C above +70°C)........................471mW
CERDIP (derate 8.00mW/°C above +70°C)................640mW
Operating Temperature Ranges
MAX1242/MAX1243_C_A..................................0°C to +70°C
MAX1242/MAX1243_E_ A..............................-40°C to +85°C
MAX1242/MAX1243_MJA ............................-55°C to +125°C
Storage Temperature Range............................-60°C to +150°C
Lead Temperature (soldering, 10sec)............................+300°C
ABSOLUTE MAXIMUM RATINGS
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ANALOG INPUT
CONVERSION RATE
DYNAMIC SPECIFICATIONS (10kHz sine-wave input, 0V to 2.5Vp-p, 73ksps, fSCLK = 2.1MHz)
DC ACCURACY (Note 1)
MAX124_B ±2
Input Voltage Range 0 VREF V
Input Capacitance
Aperture Jitter <50 ps
16 pF
MAX124_A
MAX124_B
MAX124_A
Aperture Delay tAP 30 nsFigure 9
Track/Hold Acquisition Time tACQ 1.5 µs
Throughput Rate 73 kspsfSCLK = 2.1MHz
Conversion Time
PARAMETER SYMBOL MIN TYP MAX UNITS
±1
Offset Error LSB
Differential Nonlinearity DNL ±1 LSB
±1.0
±2
Gain Error (Note 3) ±1
Resolution 10 Bits
Relative Accuracy (Note 2) ±0.5 LSB
tCONV 5.5 7.5 µs
Small-Signal Bandwidth
Signal-to-Noise Plus
Distortion Ratio SINAD 66 dB
2.25 MHz
Full-Power Bandwidth
Total Harmonic Distortion THD -70 dB
1.0
-3dB rolloff MHz
CONDITIONS
Spurious-Free Dynamic Range
ppm/°C
No missing codes over temperature
MAX124_B
±0.25
SFDR 70
Up to the 5th harmonic dB
MAX124_A
LSB
DC ACCURACY (Note1)
CONVERSION RATE
ANALOG INPUT
DYNAMIC SPECIFICATIONS (10kHz sine-wave input, 0V to 2.5p-p, 73ksps, fSCLK =2.1MHz)
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VDD = +2.7V to +5.25V; 73ksps; fSCLK = 2.1MHz (50% duty cycle); MAX1242—4.7µF capacitor at REF pin, MAX1243—external
reference; VREF = 2.5V applied to REF pin; TA= TMIN to TMAX; unless otherwise noted.)
Capacitive Bypass at REF 4.7 µF
Load Regulation (Note 5) 0.35 mV0mA to 0.2mA output load
REF Temperature Coefficient ±30 ppm/°CMAX1242
REF Short-Circuit Current 30 mA
REF Output Voltage 2.470 2.500 2.530 VTA= +25°C (Note 4)
Power-Supply Rejection (Note 7) PSR VDD = VDD(min) to VDD(max), full-scale input
1.00 VDD +
50mV
Supply Current IDD
3.0
0.8
VDD > 3.6V
ISINK = 16mA
Output Voltage High
SCLK, CS Input High Voltage VIH 2.0 V
SCLK, CS Input Low Voltage
Capacitive Bypass at REF 0.1 µF
VIL 0.8
VDD ≤3.6V
V
VOH VDD - 0.5 V
Three-State Leakage Current IL±0.01 ±10
ISOURCE = 0.5mA µA
CS = VDD
Three-State Output Capacitance COUT 15 pF
CS = VDD (Note 6)
Output Voltage Low VOL 0.4 V
PARAMETER SYMBOL MIN TYP MAX UNITS
ISINK = 5MA
SHDN Input Mid Voltage VSM 1.1 VDD - 1.1 V
SHDN Voltage, Floating VFLT VDD / 2 V
SHDN Max Allowed Leakage,
Mid Input ±100
SHDN = float
nA
SHDN = float
SCLK, CS Input Capacitance
Input Voltage Range V
CIN 15 pF
SHDN Input High Voltage VSH VDD - 0.4
(Note 6) V
SHDN Input Low Voltage VSL 0.4 V
Input Resistance
SHDN Input Current ±4.0
18 25 kΩ
REF Input Current in Shutdown
µA
SHDN = 0V or VDD
SCLK, CS Input Hysteresis VHYST
±0.01 10 µA
SHDN = 0V
CONDITIONS
Input Current
0.2 V
SCLK, CS Input Leakage IIN ±0.01 ±1
100 150 µA
µAVIN = 0V or VDD
Operating mode (MAX1242) VDD = 5.25V
Operating mode (MAX1243) VDD = 5.25V
VDD = 3.6V
Power-down VDD = 5.25V
VDD = 3.6V
Supply Voltage VDD V
VDD = 3.6V
1.9 10
3.5 15
±0.3
1.6 2.5
0.9 1.5
1.8 3.0
1.4 2.0
2.7 5.25
mA
µA
mV
Operating mode (MAX1242)
EXTERNAL REFERENCE (VREF = 2.5V)
INTERNAL REFERENCE (MAX1242 only)
DIGITAL INPUTS: SCLK, CCSS,SSHHDDNN
DIGITAL OUTPUT: DOUT
POWER REQUIREMENTS
MAX1242/MAX1243
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
4 _______________________________________________________________________________________
TIMING CHARACTERISTICS
(VDD = +2.7V to +5.25V, circuit of Figure 9, TA= TMIN to TMAX, unless otherwise noted.)
Note 1: Tested at VDD = +2.7V.
Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after the full-scale range and
offset have been calibrated.
Note 3: Offset nulled.
Note 4: Sample tested to 0.1% AQL.
Note 5: External load should not change during conversion for specified accuracy.
Note 6: Guaranteed by design. Not subject to production testing.
Note 7: Measured as [VFS (VDD(min)) - VFS (VDD(max))].
Note 8: To guarantee acquisition time, tACQ is the maximum time the device takes to acquire the signal, and is also the minimum
time needed for the signal to be acquired.
DOUT DOUT
6k
DGND
CLOAD = 50pF CLOAD = 50pF
6k
DGND
+2.7V
b) High-Z to VOL and VOH to VOL
a) High-Z to VOH and VOL to VOH
DOUT DOUT
6k
DGND
CLOAD = 50pF CLOAD = 50pF
6k
DGND
+2.7V
b) VOLto High-Za) VOH to High-Z
Figure 1. Load Circuits for DOUT Enable Time
Figure 2. Load Circuits for DOUT Disable Time
MAX124_ _M
MAX124_ _C/E
Figure 1, CLOAD = 50pF
Figure 1,
CLOAD = 50pF
CS = VDD (Note 8)
Figure 2, CLOAD = 50pF
CONDITIONS
ns240tDV
CS Fall to Output Enable
ns
20 200
tDO
µs1.5tACQ
Acquisition Time
SCLK Fall to Output Data Valid
ns240tCS
CS Pulse Width ns0tSTR
DOUT Rise to SCLK Rise (Note 6) ns50tCS0
SCLK Low to CS Fall Setup Time
ns240tTR
CS Rise to Output Disable MHz0 2.1fSCLK
SCLK Clock Frequency ns200tCH
SCLK Pulse Width High ns200tCL
SCLK Pulse Width Low
UNITSMIN TYP MAX
SYMBOLPARAMETER
20 240
MAX1242/MAX1243
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
_______________________________________________________________________________________
5
2.00
0.502.25 2.75
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
1.75
1.25
1.50
1.00
0.75
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
3.75 5.253.25 4.25 4.75
MAX1242/43-01
RL = ∞
CODE = 1010101000
MAX1243
MAX1242
CLOAD = 20pF
CLOAD = 50pF
CLOAD = 50pF
CLOAD = 20pF
4.0
3.5
02.25 2.75
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
3.0
2.5
1.5
2.0
1.0
0.5
SUPPLY VOLTAGE (V)
SHUTDOWN SUPPLY CURRENT (µA)
3.75 5.253.25 4.25 4.75
MAX1242/43-02
MAX1242/MAX1243
2.5015
2.49852.25
INTERNAL REFERENCE VOLTAGE
vs. SUPPLY VOLTAGE
2.5000
2.5010
2.5005
2.4995
2.4990
SUPPLY VOLTAGE (V)
INTERNAL REFERENCE VOLTAGE (V)
3.752.75 3.25
MAX1242/43-03
MAX1242
0.8
0.9
1.0
1.1
1.2
1.3
-60 -20 20 60 100 140
SUPPLY CURRENT vs. TEMPERATURE
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
MAX1242/43-04
MAX1243
MAX1242
RLOAD = ∞
CODE = 1010101000
0
0.10
0.05
0.20
0.15
0.25
0.30
2.25 3.25 3.752.75 4.25 4.75 5.25
INTEGRAL NONLINEARITY
vs. SUPPLY VOLTAGE
MAX1242/43-07
SUPPLY VOLTAGE (V)
INL (LSB)
MAX1242
MAX1243
1.00
1.50
1.25
1.75
2.25
2.00
2.75
2.50
3.00
-60 -20 20 60 100 140
SHUTDOWN CURRENT
vs. TEMPERATURE
TEMPERATURE (°C)
SHUTDOWN CURRENT (µA)
MAX1242/43-05
2.494
2.495
2.496
2.497
2.498
2.499
2.500
2.501
-60 -20-40 200 6040 100 12080 140
INTERNAL REFERENCE VOLTAGE
vs. TEMPERATURE
TEMPERATURE (°C)
INTERNAL REFERENCE VOLTAGE (V)
MAX1242/43-06
VDD = 2.7V
VDD = 5V VDD = 3.6V
MAX1242
0
0.15
0.10
0.05
0.20
0.25
0.30
-60 200-40 -20 40 60 80 100 120 140
INTEGRAL NONLINEARITY
vs. TEMPERATURE
MAX1242/43-08
TEMPERATURE (°C)
INL (LSB)
VDD = 2.7V
MAX1242
MAX1243
0.15
INTEGRAL NONLINEARITY
vs. CODE
-0.15
0
-0.05
-0.10
0.10
0.05
MAX1242/43-09
INL (LSB)
CODE
256 512 768 10240
__________________________________________Typical Operating Characteristics
(VDD = +3.0V, VREF = 2.5V, fSCLK = 2.1MHz, CLOAD = 20pF, TA= +25°C, unless otherwise noted.)
MAX1242/MAX1243
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
6 _______________________________________________________________________________________
_______________Detailed Description
Converter Operation
The MAX1242/MAX1243 use an input track/hold (T/H)
and successive-approximation register (SAR) circuitry
to convert an analog input signal to a digital 10-bit out-
put. Figure 3 shows the MAX1242/MAX1243 in their
simplest configuration. The MAX1242/MAX1243 convert
input signals in the 0V to VREF range in 9µs, including
T/H acquisition time. The MAX1242’s internal reference
is trimmed to 2.5V, while the MAX1243 requires an
external reference. Both devices accept external refer-
ence voltages from 1.0V to VDD. The serial interface
requires only three digital lines (SCLK,
CS,
and DOUT)
and provides an easy interface to microprocessors
(µPs).
The MAX1242/MAX1243 have two modes: normal and
shutdown. Pulling
SHDN
low shuts the device down and
reduces supply current below 10µA (VDD ≤3.6V), while
pulling
SHDN
high or leaving it open puts the devices
into operational mode. A conversion is initiated by
pulling CS low. The conversion result is available at
DOUT in unipolar serial format. The serial-data stream
consists of a high bit, signaling the end of conversion
(EOC), followed by the data bits (MSB first).
Analog Input
Figure 4 illustrates the sampling architecture of the ana-
log-to-digital converter’s (ADC’s) comparator. The full-
scale input voltage is set by the voltage at REF.
Track/Hold
In track mode, the analog signal is acquired and stored
in the internal hold capacitor. In hold mode, the T/H
switch opens and maintains a constant input to the
ADC’s SAR section.
During acquisition, the analog input AIN charges
capacitor CHOLD. Bringing
CS
low ends the acquisition
interval. At this instant, the T/H switches the input side
of CHOLD to GND. The retained charge on CHOLD repre-
sents a sample of the input, unbalancing node ZERO at
the comparator’s input.
In hold mode, the capacitive digital-to-analog converter
(DAC) adjusts during the remainder of the conversion
cycle to restore node ZERO to 0V within the limits of 10-
bit resolution. This action is equivalent to transferring a
charge from CHOLD to the binary-weighted capacitive
DAC, which in turn forms a digital representation of the
analog input signal. At the conversion’s end, the input
side of CHOLD switches back to AIN, and CHOLD
charges to the input signal again.
The time required for the T/H to acquire an input signal
is a function of how quickly its input capacitance is
charged. If the input signal’s source impedance is high,
the acquisition time lengthens, and more time must be
allowed between conversions. The acquisition time,
tACQ, is the maximum time the device takes to acquire
the signal and the minimum time needed for the signal
to be acquired. Acquisition time is calculated by:
tACQ = 7(RS+ RIN) x 16pF
______________________________________________________________Pin Description
6 DOUT Serial-Data Output. Data changes state at SCLK’s falling edge. High impedance when CS is high.
8 SCLK
3SHDN
Three-Level Shutdown Input. Pulling SHDN low shuts the MAX1242/MAX1243 down to 15µA (max)
supply current. Both MAX1242 and MAX1243 are fully operational with either SHDN high or floating.
For the MAX1242, pulling SHDN high enables the internal reference, and letting SHDN float disables
the internal reference and allows for the use of an external reference.
4 REF Reference Voltage for Analog-to-Digital Conversion. Internal 2.5V reference output for MAX1242;
bypass with a 4.7µF capacitor. External reference voltage input for MAX1243, or for MAX1242 with the
internal reference disabled. Bypass REF with a minimum of 0.1µF when using an external reference.
7CS Active-Low Chip Select. Initiates conversions on the falling edge. When CS is high, DOUT is high
impedance.
5 GND Analog and Digital Ground
2 AIN Sampling Analog Input, 0V to VREF range
NAME FUNCTION
1 VDD Positive Supply Voltage: +2.7V to +5.25V
PIN
Serial-Clock Input. SCLK clocks data out at rates up to 2.1MHz.
MAX1242/MAX1243
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
_______________________________________________________________________________________ 7
AIN TRACK INPUT
HOLD
GND
TRACK HOLD
9k
RIN
CHOLD
16pF
- +
CSWITCH
COMPARATOR
ZERO
REF CAPACITIVE DAC
AT THE SAMPLING INSTANT,
THE INPUT SWITCHES FROM
AIN TO GND.
SHUTDOWN
INPUT
ANALOG INPUT
0V TO VREF
+2.7V to +5.25V
1
2
3
4
VDD
AIN
SHDN
REF
8
7
6
5
SCLK
CS
DOUT
GND
SERIAL
INTERFACE
C*
*4.7µF, MAX1242
0.1µF, MAX1243
4.7µF0.1µF
REFERENCE
INPUT
MAX1243
MAX1242
MAX1243
Figure 3. Operational Diagram Figure 4. Equivalent Input Circuit
where RIN = 9kΩ, RS= the input signal’s source imped-
ance, and tACQ is never less than 1.5µs. Source imped-
ances below 4kΩdo not significantly affect the ADC’s
AC performance.
Higher source impedances can be used if a 0.01µF
capacitor is connected to the analog input. Note that
the input capacitor forms an RC filter with the input
source impedance, limiting the ADC’s input signal
bandwidth.
Input Bandwidth
The ADC’s input tracking circuitry has a 2.25MHz
small-signal bandwidth, so it is possible to digitize
high-speed transient events and measure periodic sig-
nals with bandwidths exceeding the ADC’s sampling
rate by using undersampling techniques. To avoid
aliasing of unwanted high-frequency signals into the
frequency band of interest, anti-alias filtering is recom-
mended.
Analog Input Protection
Internal protection diodes, which clamp the analog
input to VDD and GND, allow the input to swing from
GND - 0.3V to VDD + 0.3V without damage. However,
for accurate conversions near full scale, the input must
not exceed VDD by more than 50mV, or be lower than
GND by 50mV.
If the analog input exceeds 50mV beyond the supplies,
limit the input current to 2mA.
Internal Reference (MAX1242)
The MAX1242 has an on-chip voltage reference
trimmed to 2.5V. The internal reference output is con-
nected to REF and also drives the internal capacitive
DAC. The output can be used as a reference voltage
source for other components and can source up to
400µA. Bypass REF with a 4.7µF capacitor. Larger
capacitors increase wake-up time when exiting shut-
down (see
Using SHDN to Reduce Supply Current
).
The internal reference is enabled by pulling the SHDN
pin high. Letting SHDN float disables the internal refer-
ence, which allows the use of an external reference, as
described in the
External Reference
section.
External Reference
The MAX1242/MAX1243 operate with an external refer-
ence at the REF pin. To use the MAX1242 with an
external reference, disable the internal reference by let-
ting SHDN float. Stay within the voltage range 1.0V to
VDD to achieve specified accuracy. The minimum input
impedance is 18kΩfor DC currents. During conver-
sion, the external reference must be able to deliver up
to 250µA of DC load current and have an output
impedance of 10Ωor less. The recommended mini-
mum value for the bypass capacitor is 0.1µF. If the ref-
erence has higher output impedance or is noisy,
bypass it close to the REF pin with a 4.7µF capacitor.
MAX1242/MAX1243
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
8 _______________________________________________________________________________________
Serial Interface
Initialization after Power-Up and
Starting a Conversion
When power is first applied, and if SHDN is not pulled
low, it takes the fully discharged 4.7µF reference
bypass capacitor up to 20ms to provide adequate
charge for specified accuracy. With an external refer-
ence, the internal reset time is 10µs after the power
supplies have stabilized. No conversions should be
performed during these times.
To start a conversion, pull
CS
low. At
CS’s
falling edge,
the T/H enters its hold mode and a conversion is initiat-
ed. After an internally timed conversion period, the end
of conversion is signaled by DOUT pulling high. Data
can then be shifted out serially with the external clock.
Using
SSHHDDNN
to Reduce Supply Current
Power consumption can be reduced significantly by
shutting down the MAX1242/MAX1243 between con-
versions. Figure 6 shows a plot of average supply cur-
rent vs. conversion rate. Because the MAX1243 uses
an external reference voltage (assumed to be present
continuously), it “wakes up” from shutdown more quick-
ly, providing lower average supply currents. The wake-
up time, tWAKE, is the time from SHDN deasserted to
the time when a conversion may be initiated (Figure 5).
For the MAX1242, this time depends on the time in
shutdown (Figure 7) because the external 4.7µF refer-
ence bypass capacitor loses charge slowly during
shutdown. The MAX1243’s wake-up time is largely
dependent on the external reference’s power-up time. If
the external reference is not shut down, the wake-up
time is approximately 4µs.
Figure 6. Average Supply Current vs. Conversion Rate
Figure 7. Typical Reference-Buffer Power-Up Delay vs. Time in
Shutdown
COMPLETE CONVERSION SEQUENCE
tWAKE
POWERED UPPOWERED DOWNPOWERED UP
CONVERSION 0 CONVERSION 1
DOUT
CS
SHDN
Figure 5. Shutdown Sequence
MAX1242/MAX1243
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
_______________________________________________________________________________________ 9
EOC
INTERFACE IDLE CONVERSION
IN PROGRESS EOC
0µs
TRAILING
ZEROS
SUB
BITS IDLE
CLOCK OUT SERIAL DATA
TRACK/HOLD
STATE TRACK HOLD
TRACK
DOUT B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 S1 S0
SCLK 1 4 8 12 16
7.5µs (tCONV)
HOLD
0µs(tCS)
TOTAL = 13.7µs
12.5 × 0.476µs = 5.95µs
CYCLE TIME
CS
0.24µs
Figure 8a. Interface Timing Sequence
EOC
INTERFACE IDLE CONVERSION
IN PROGRESS EOC
0µs
IDLE
CLOCK OUT SERIAL DATA
TRACK/HOLD
STATE TRACK HOLD
TRACK
DOUT B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
SCLK 1 4 8
7.5µs (tCONV)
HOLD
(tCS)
TOTAL = 12.74µs
10.5 × 0.476µs = 5µs
CYCLE TIME
CS
0.24µs
Figure 8b. Interface Timing Sequence—Minimum Cycle Time
…
…
…
…
CS
SCLK
DOUT
INTERNAL
T/H (TRACK/ACQUIRE)
tCS0
tCONV
tDV
tSTR
tAP
(HOLD) (TRACK/ACQUIRE)
B0 S1 S0
tCH
tDO tCL tTR
tCS
Figure 9. Detailed Serial-Interface Timing
MAX1242/MAX1243
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
10 ______________________________________________________________________________________
External Clock
The actual conversion does not require the external
clock. This allows the conversion result to be read back
at the µP’s convenience at any clock rate up to
2.1MHz. The clock duty cycle is unrestricted if each
clock phase is at least 200ns. Do not run the clock
while a conversion is in progress.
Timing and Control
Conversion-start and data-read operations are con-
trolled by the
CS
and SCLK digital inputs. The timing
diagrams of Figures 8 and 9 outline serial-interface
operation.
A
CS
falling edge initiates a conversion sequence: the
T/H stage holds the input voltage, the ADC begins to
convert, and DOUT changes from high impedance to
logic low. SCLK must be kept low during the conver-
sion. An internal register stores the data when the con-
version is in progress.
EOC is signaled by DOUT going high. DOUT’s rising
edge can be used as a framing signal. SCLK shifts the
data out of this register any time after the conversion is
complete. DOUT transitions on SCLK’s falling edge.
The next falling clock edge produces the MSB of the
conversion at DOUT, followed by the remaining bits.
Since there are 10 data bits, two sub-bits, and one
leading high bit, at least 13 falling clock edges are
needed to shift out these bits. Extra clock pulses occur-
ring after the conversion result has been clocked out,
and prior to a rising edge of
CS
, produce trailing zeros
at DOUT and have no effect on converter operation.
For minimum cycle time, use DOUT’s rising edge as
the EOC signal and then clock out the data with 10.5
clock cycles at full speed (Figure 8b). Pull
CS
high after
reading the conversion’s LSB. After the specified mini-
mum time, tCS, pull
CS
low again to initiate the next
conversion.
Output Coding and Transfer Function
The data output from the MAX1242/MAX1243 is binary.
Figure 10 depicts the nominal transfer function. Code
transitions occur halfway between successive-integer
LSB values. If VREF = 2.5V, then 1LSB = 2.44mV or
2.5V / 1024.
__________Applications Information
Connection to Standard Interfaces
The MAX1242/MAX1243 serial interface is fully compat-
ible with SPI, QSPI, and Microwire standard serial inter-
faces (Figure 11).
CS
SCLK
DOUT
I/O
SCK
MISO +3V
SS
a) SPI
CS
SCLK
DOUT
CS
SCK
MISO +3V
SS
b) QSPI
MAX1242
MAX1243
MAX1242
MAX1243
MAX1242
MAX1243
CS
SCLK
DOUT
I/O
SK
SI
c) MICROWIRE
Figure 11. Common Serial-Interface Connections to the
MAX1242/MAX1243
Figure 10. Unipolar Transfer Function, Full Scale (FS) =
VREF - 1LSB, Zero Scale (ZS) = GND
11…111
11…110
11…101
00…011
00…010
00…001
00…000 0 1 2 FS
OUTPUT CODE
FS - 3/2LSBINPUT VOLTAGE (LSB)
FS = VREF - 1LSB
1LSB = VREF
1024
FULL-SCALE
TRANSITION
3
If a serial interface is available, set the CPU’s serial
interface in master mode so the CPU generates the ser-
ial clock. Choose a clock frequency up to 2.1MHz.
1) Use a general-purpose I/O line on the CPU to pull
CS
low. Keep SCLK low.
2) Wait the maximum conversion time specified before
activating SCLK. Alternatively, look for a DOUT rising
edge to determine the end of conversion.
3) Activate SCLK for a minimum of 11 clock cycles. The
first falling clock edge produces the MSB of the
DOUT conversion. DOUT output data transitions on
SCLK’s falling edge and is available in MSB-first for-
mat. Observe the SCLK-to-DOUT valid timing char-
acteristic. Data can be clocked into the µP on
SCLK’s rising edge.
4) Pull
CS
high at or after the 11th falling clock edge. If
CS
remains low, the two sub-bits and trailing zeros
are clocked out after the LSB.
5) With
CS
= high, wait the minimum specified time, tCS,
before initiating a new conversion by pulling
CS
low.
If a conversion is aborted by pulling
CS
high before
the conversion’s end, wait the minimum acquisition
time, tACQ, before starting a new conversion.
Data can be output in two bytes or continuously, as
shown in Figures 8a and 8b. The bytes contain the
result of the conversion padded with one leading 1, two
sub-bits, and trailing 0s if SCLK is still active with CS
kept low.
SPI and Microwire
When using SPI or QSPI, set CPOL = 0 and CPHA = 0.
Conversion begins with a
CS
falling edge. DOUT goes
low, indicating a conversion is in progress. Wait until
DOUT goes high or until the maximum specified 7.5µs
conversion time elapses. Two consecutive 1-byte reads
are required to get the full 10+2 bits from the ADC.
DOUT output data transitions on SCLK’s falling edge
and is clocked into the µP on SCLK’s rising edge.
The first byte contains a leading 1, and seven bits of
conversion result. The second byte contains the remain-
ing three bits, two sub-bits, and three trailing zeros. See
Figure 11 for connections and Figure 12 for timing.
QSPI
Set CPOL = CPHA = 0. Unlike SPI, which requires two
1-byte reads to acquire the 10 bits of data from the ADC,
QSPI allows the minimum number of clock cycles neces-
sary to clock in the data. The MAX1242/MAX1243 require
11 clock cycles from the µP to clock out the 10 bits of
data. Additional clock cycles clock out the two sub-bits
followed by trailing zeros (Figure 13). The maximum clock
frequency to ensure compatibility with QSPI is 2.097MHz.
Layout and Grounding
For best performance, use printed circuit boards. Wire-
wrap boards are not recommended. Board layout
should ensure that digital and analog signal lines are
separated from each other. Do not run analog and digi-
tal (especially clock) lines parallel to one another, or
digital lines underneath the ADC package.
MAX1242/MAX1243
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
______________________________________________________________________________________ 11
D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 S1 S0 HIGH-Z
tCONV
DOUT
CS
SCLK
1ST BYTE READ 2ND BYTE READ
EOC
MSB LSB
D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 S1 S0 HIGH-Z
tCONV
DOUT
CS
SCLK
EOC
MSB LSB
Figure 12. SPI/Microwire Serial-Interface Timing (CPOL = CPHA = 0)
Figure 13. QSPI Serial-Interface Timing (CPOL = CPHA = 0)
MAX1242/MAX1243
+2.7V to +5.25V, Low-Power, 10-Bit
Serial ADCs in SO-8
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Ordering Information (continued)
TRANSISTOR COUNT: 2559
SUBSTRATE CONNECTED TO GND
___________________Chip Information
________________________________________________________Package Information
*
Contact factory for availability and processing to MIL-STD-883.
Note:
Order the MAX1242A in place of the MAX1242C. Order the
MAX1242B in place of the MAX1242D.
PDIPN.EPS
SOICN.EPS
±1/28 SO0°C to +70°CMAX1243ACSA ±1
±1
±1/2
8 SO
8 Plastic DIP
8 Plastic DIP0°C to +70°C
0°C to +70°C
0°C to +70°CMAX1243BCSA
MAX1243BCPA
MAX1243ACPA
±1/28 CERDIP*-55°C to +125°CMAX1242AMJA
±18 CERDIP*-55°C to +125°CMAX1243BMJA ±1/28 CERDIP*-55°C to +125°CMAX1243AMJA ±1
±1
±1
±1/2
INL
(LSB)
8 SO-40°C to +85°CMAX1243BESA ±1/28 SO-40°C to +85°CMAX1243AESA ±18 Plastic DIP-40°C to +85°CMAX1243BEPA ±1/28 Plastic DIP-40°C to +85°CMAX1243AEPA
8 CERDIP*
8 SO
8 SO
PIN-
PACKAGE
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
-55°C to +125°CMAX1242BMJA
MAX1242BESA
MAX1242AESA
PART