General Description
The MAX3387E 3V powered TIA/EIA-232 and V.28/V.24
is a communications interface with low power require-
ments, high data-rate capabilities, and enhanced elec-
trostatic discharge (ESD) protection. The MAX3387E
has three receivers and three transmitters. All RS-232
inputs and outputs are protected to ±15kV using the
IEC 1000-4-2 Air-Gap Discharge method, ±8kV using
the IEC 1000-4-2 Contact Discharge method, and
±15kV using the Human Body Model.
A proprietary low-dropout transmitter output stage
enables true RS-232 performance from a +3.0V to
+5.5V supply with a dual charge pump. The charge
pump requires only four small 0.1µF capacitors for
operation from a +3.3V supply. The MAX3387E is capa-
ble of running at data rates up to 250kbps while main-
taining RS-232 compliant output levels.
The MAX3387E has a unique VLpin that allows interop-
eration in mixed-logic voltage systems. Both input and
output logic levels are pin programmable through the
VLpin. The MAX3387E is available in a space-saving
TSSOP package.
Applications
Subnotebook/Palmtop Computers
PDAs and PDA Cradles
Cell Phone Data Cables
Battery-Powered Equipment
Hand-Held Equipment
Peripherals
Features
♦VLPin for Compatibility with Mixed-Voltage
Systems
♦±15kV ESD Protection on Rx Inputs and Tx Outputs
♦Low 300µA Supply Current
♦Guaranteed 250kbps Data Rate
♦1µA AutoShutdown Plus™ with Receivers Active
♦Meets TIA/EIA-232 Specifications Down to 3.0V
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
_______________________________________________________________
Maxim Integrated Products
1
C1
0.1μF
C2
0.1μF
MAX3387E
R2OUT13
R1OUT14
R2IN 17
GND
22
RS-232
OUTPUTS
TTL/CMOS
INPUTS T2IN
8
T1IN
7
C2-
5
C2+
4
C1-
3
C1+
1
R1IN 18
T2OUT 20
T1OUT 21
V- 6
V+ 2
VCC VL
C4
0.1μF
23 15
CBYPASS
+3.3V
T3IN
10 T3OUT 19
RS-232
INPUTS
TTL/CMOS
OUTPUTS
C3
0.1μF
5k
5k
VL
VL
R3OUT12 R3IN 16
5k
VL
FORCEOFF
24
INVALID
9
11
FORCEON
Typical Operating Circuit
19-1561; Rev 3; 6/10
Ordering Information
AutoShutdown Plus is a trademark of Maxim Integrated
Products, Inc.
PART
MAX3387ECUG+
MAX3387EEUG+
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
24 TSSOP
24 TSSOP
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
DC ELECTRICAL CHARACTERISTICS
(VCC = VL= +3.0V to +5.5V; C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2–C4 = 0.33µF, tested at +5.0V ±10%;
TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VL= +3.3V, TA= +25°C.)
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.
Note 1: V+ and V- can have maximum magnitudes of 7V, but their absolute difference cannot exceed 13V.
VCC to GND..............................................................-0.3V to +6V
VLto GND...................................................-0.3V to (VCC + 0.3V)
V+ to GND ................................................................-0.3V to +7V
V- to GND .................................................................+0.3V to -7V
V+ +⏐V-⏐(Note 1) .............................................................. +13V
Input Voltages
T_IN, FORCEON, FORCEOFF to GND ..................-0.3V to +6V
R_IN to GND .....................................................................±25V
Output Voltages
T_OUT to GND...............................................................±13.2V
R_OUT........................................................-0.3V to (VL+ 0.3V)
Short-Circuit Duration T_OUT to GND........................Continuous
Continuous Power Dissipation (TA= +70°C)
24-Pin TSSOP (derate 12.2mW/°C above +70°C) ........976mW
Operating Temperature Ranges
MAX3387ECUG ...................................................0°C to +70°C
MAX3387EEUG ................................................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
IOUT = 1.6mA
All R_IN idle, FORCEON = GND,
FORCEOFF = VCC, all T_IN idle
T_IN, FORCEON, FORCEOFF
T_IN, FORCEON,
FORCEOFF
FORCEOFF = FORCEON = VCC, no load
CONDITIONS
V0.4Output Voltage Low
µA±0.01 ±1Input Leakage Current
V0.5Transmitter Input Hysteresis
V
0.9
Input Logic Threshold High 1.4
2.0
µA1.0 10
Supply Current, AutoShutdown
Plus
2.4
V
0.8
0.3 1 mASupply Current
UNITSMIN TYP MAXSYMBOLPARAMETER
VL= +5.0V
VL= +3.3V
VL= +2.5V
VL= +1.8V
IOUT = -1mA V
VL- VL-
0.6 0.1
Output Voltage High
VL= +3.3V or +5.0V
T_IN, FORCEON,
FORCEOFF 0.6
Input Logic Threshold Low VL= +2.5V
V-25 +25Input Voltage Range
TA= +25°C V
0.8 1.5
Input Threshold Low VL= +5.0V
VL= +3.3V 0.6 1.2
TA= +25°C V
1.8 2.4
Input Threshold High VL= +5.0V
VL= +3.3V 1.5 2.4
DC CHARACTERISTICS (VCC = +3.3V or +5V, TA= +25°C)
LOGIC INPUTS
RECEIVER OUTPUTS
RECEIVER INPUTS
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
_______________________________________________________________________________________ 3
DC ELECTRICAL CHARACTERISTICS (continued)
(VCC = VL= +3.0V to +5.5V; C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2–C4 = 0.33µF, tested at +5.0V ±10%;
TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VL= +3.3V, TA= +25°C.)
AutoShutdown Plus (FORCEON = GND, FORCEOFF = VCC)
ESD PROTECTION
TRANSMITTER OUTPUTS
-2.7Negative threshold
Figure 3a
Positive threshold
Receiver or Transmitter Edge to
Transmitters Shutdown t
AUTOSHDN
15 30 60 s
Receiver Positive or Negative
Threshold to INVALID Low tINVL 30
VCC = +5V, Figure 3b
Receiver or Transmitter Edge to
Transmitters Enabled tWU 100
µsVCC = +5V, Figure 3b
µsVCC = +5V, Figure 3b
Receiver Positive or Negative
Threshold to INVALID High tINVH 1µs
INVALID Output Voltage Low 0.4
VCC = +5V, Figure 3b
INVALID Output Voltage High VL- 0.6
VIOUT = -1.6mA
VIOUT = -1.0mA
Receiver Input Threshold to
INVALID Output Low -0.3 0.3 V
Receiver Input Threshold to
INVALID Output High
2.7 V
Figure 3a
R_IN, T_OUT
ESD Protection
±8
kV
IEC 1000-4-2 Contact Discharge method
PARAMETER SYMBOL MIN TYP MAX UNITS
Input Hysteresis 0.5 V
Input Resistance 357kΩ
Output Voltage Swing ±5 ±5.4 V
Output Resistance 300 10M Ω
Output Short-Circuit Current ±60 mA
Output Leakage Current ±25 µA
±15
±15
CONDITIONS
TA= +25°C
All transmitter outputs loaded with 3kΩto
ground
VCC = V+ = V- = 0V, transmitter output = ±2V
VT_OUT = 0V
VT_OUT = ±12V, transmitters disabled;
VCC = 0V or +3.0V to +5.5V
Human Body Model
IEC 1000-4-2 Air-Gap Discharge method
TRANSMITTER OUTPUTS
ESD PROTECTION
AutoShutdown Plus (FORCEON = GND, FORCEOFF = VCC)
-7.5
-5.0
-2.5
0
2.5
5.0
7.5
0 1000 2000 3000 4000 5000
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE
MAX3387E-01
LOAD CAPACITANCE (pF)
OUTPUT VOLTAGE (V)
DATA RATE = 250kbps
LOAD = 3kΩ IN PARALLEL WITH CL
0
2
4
6
8
10
12
14
16
0 1000 2000 3000 4000 5000
SLEW RATE vs. LOAD CAPACITANCE
MAX3387E-02
LOAD CAPACITANCE (pF)
SLEW RATE (V/µs)
SLEW RATE +
SLEW RATE -
Typical Operating Characteristics
(VCC = VL= +3.3V, TA = +25°C, unless otherwise noted.)
CL= 150pF to
1000pF
CL= 150pF to
2500pF
VCC = +3.3V,
TA= +25°C,
RL= 3kΩto 7kΩ,
measured from +3V
to -3V or -3V to +3V
RL= 3kΩ, CL= 1000pF,
one transmitter switching
(Note 2)
V/µs
430
⏐VT_OUT⏐> +3.7V
Transition-Region Slew
Rate
Receiver input to receiver output,
CL= 150pF
CONDITIONS
630
ns50
⏐tPHL - tPLH⏐
Receiver Skew
ns100
⏐tPHL - tPLH⏐
Transmitter Skew
µs
100Time to Exit Shutdown
µs
0.15tPLH
Receiver Propagation Delay
kbps250Maximum Data Rate
0.15tPHL
UNITSMIN TYP MAXSYMBOLPARAMETER
TIMING CHARACTERISTICS
(VCC = VL= +3V to +5.5V; C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2–C4 = 0.33µF, tested at +5.0V ±10%; TA= TMIN
to TMAX, unless otherwise noted. Typical values are at VCC = VL= +3.3V, TA= +25°C.)
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
4 _______________________________________________________________________________________
Note 2: Transmitter skew is measured at the transmitter zero crosspoints.
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
_______________________________________________________________________________________
5
-7.5
-5.0
-2.5
0
2.5
5.0
7.5
0 50 100 150 200 250
TRANSMITTER OUTPUT VOLTAGE
vs. DATA RATE
MAX3387E-03
DATA RATE (kbps)
OUTPUT VOLTAGE (V)
LOAD = 3kΩ, 1000pF
ONE TRANSMITTER
SWITCHING AT DATA
RATE, OTHER
TRANSMITTERS
AT 1/8 DATA RATE
0
10
20
30
40
50
60
0 1000 2000 3000 4000 5000
SUPPLY CURRENT vs. LOAD CAPACITANCE
MAX3387E-04
LOAD CAPACITANCE (pF)
SUPPLY CURRENT (mA)
250kbps
120kbps
20kbps
LOAD = 3kΩ,
ONE TRANSMITTER
SWITCHING AT DATA
RATE, OTHER
TRANSMITTERS
AT 1/8 DATA RATE
Typical Operating Characteristics (continued)
(VCC = VL= +3.3V, TA = +25°C, unless otherwise noted.)
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
FORCEOFF
VCC
GND
T1OUTC2+
C1-
V+
C1+
TOP VIEW
T2OUT
T3OUT
R1IN
R2INT2IN
T1IN
V-
C2-
16
15
14
13
9
10
11
12
R3IN
VL
R1OUT
R2OUTR3OUT
FORCEON
T3IN
INVALID
TSSOP
MAX3387E
+
Pin Configuration
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
6 _______________________________________________________________________________________
C1+ Positive Terminal of the Voltage-Doubler Charge-Pump Capacitor
Pin Description
V+ +5.5V Supply Generated by the Charge Pump
C1- Negative Terminal of the Voltage-Doubler Charge-Pump Capacitor
C2+ Positive Terminal of the Inverting Charge-Pump Capacitor
C2- Negative Terminal of the Inverting Charge-Pump Capacitor
V- -5.5V Generated by the Charge Pump
T1IN TTL/CMOS Transmitter Inputs
R3OUT
TTL/CMOS Receiver Outputs. Swing between 0V and VL.
R2OUT
R1OUT
VLLogic-Level Supply. All CMOS inputs and outputs are referenced to this supply.
R3IN
R2IN
R1IN
RS-232 Receiver Inputs
T3OUT
T2OUT
T1OUT
RS-232 Transmitter Outputs
GND Ground
VCC +3.0V to +5.5V Supply Voltage
NAME FUNCTION
FORCEOFF Force-Off Input. Drive FORCEOFF low to shut down transmitters and on-board power sup-
ply. This overrides all automatic circuitry and FORCEON (Table 1).
1
2
3
4
5
6
7
12
13
14
15
16
17
18
19
20
21
22
23
PIN
24
FORCEON Force-On Input. Drive FORCEON high to override automatic circuitry keeping transmitters
on (FORCEOFF must be high) (Table 1).
11
INVALID Output of the Valid Signal Detector. INVALID is high if a valid RS-232 signal is present on
the receiver inputs.
9
T3IN TTL/CMOS Transmitter Inputs10
8T2IN
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
_______________________________________________________________________________________ 7
Detailed Description
Dual Charge-Pump
Voltage Converter
The MAX3387E’s internal power supply consists of a
regulated dual charge pump that provides output volt-
ages of +5.5V (doubling charge pump) and -5.5V
(inverting charge pump), regardless of the input volt-
age (VCC) over a +3.0V to +5.5V range. The charge
pumps operate in a discontinuous mode: if the output
voltages are less than 5.5V, the charge pumps are
enabled; if the output voltages exceed 5.5V, the charge
pumps are disabled. Each charge pump requires a fly-
ing capacitor (C1, C2) and a reservoir capacitor (C3,
C4) to generate the V+ and V- supplies.
RS-232 Transmitters
The transmitters are inverting level translators that con-
vert CMOS-logic levels to 5.0V EIA/TIA-232 levels.
The MAX3387E transmitters guarantee a 250kbps data
rate with worst-case loads of 3kΩin parallel with
1000pF, providing compatibility with PC-to-PC commu-
nication software (such as Laplink®). Transmitters can
be paralleled to drive multiple receivers or mice. Figure 1
shows a complete system connection.
These RS-232 output stages are turned off (high imped-
ance) when the device is in shutdown mode. When the
power is off, the MAX3387E permits the outputs to be
driven up to ±12V.
The transmitter inputs do not have pull-up resistors.
Connect unused inputs to GND or VL.
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic
output levels. The MAX3387E’s receivers are always
active, even when the device is in shutdown.
The MAX3387E features an INVALID output that indi-
cates when no signal is present on any RS-232 receiver
inputs. INVALID is independent of other control logic
functions; it indicates the receiver input conditions only
(Figures 2 and 3).
MAX3387E
I/O
CHIP
WITH
UART
CPU
RS-232
POWER-
MANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
VL
VCC
I/O CHIP
POWER SUPPLY
FORCEOFF
FORCEON
INVALID
Figure 1. Interface Under Control of PMU
Laplink is a registered trademark of Laplink Software, Inc.
+0.3V
-0.3V
INVALID
R_IN
TRANSMITTERS ARE DISABLED, REDUCING SUPPLY CURRENT TO 1μA IF
ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR AT LEAST 30μs.
30
μ
s
COUNTER
R
+2.7V
-2.7V
INVALID
R_IN
TRANSMITTERS ARE ENABLED IF:
ANY RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V;
ANY RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR LESS THAN 30μs.
30
μ
s
COUNTER
R
Figure 2a. INVALID Function Diagram, INVALID = Low
Figure 2b. INVALID Function Diagram, INVALID = High
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
8 _______________________________________________________________________________________
AutoShutdown Plus Mode
The MAX3387E achieves a1µA supply current with
Maxim’s AutoShutdown Plus feature, which operates
when FORCEOFF is high and a FORCEON is low. When
these devices do not sense a valid signal transition on
any receiver and transmitter input for 30sec, the on-
board charge pumps are shut down, reducing supply
current to 1µA. This occurs if the RS-232 cable is dis-
connected or if the connected peripheral transmitters
are turned off, and if the UART driving the transmitter
inputs is inactive. The system turns on again when a
valid transition is applied to any RS-232 receiver or
transmitter input. As a result, the system saves power
without changes to the existing BIOS or operating sys-
tem.
Figure 3a shows valid and invalid RS-232 receiver volt-
age levels. INVALID indicates the receiver input’s con-
dition, and is independent of FORCEON and
FORCEOFF states. Figure 2 and Table 1 summarize the
MAX3387E’s operating modes. FORCEON and FORCE-
OFF override AutoShutdown Plus circuitry. When nei-
ther control is asserted, the IC selects between these
states automatically based on the last receiver or trans-
mitter input edge received.
By connecting FORCEON to INVALID, the MAX3387E
shuts down when no valid receiver level and no receiver or
transmitter edge is detected for 30sec, and wakes up
when a valid receiver level or receiver or transmitter
edge is detected.
By connecting FORCEON and FORCEOFF to INVALID,
the MAX3387E shuts down when no valid receiver level
is detected.
A mouse or other system with AutoShutdown Plus may
need time to wake up. Figure 4 shows a circuit that
forces the transmitters on for 100ms, allowing enough
time for the other system to realize that the MAX3387E
is awake. If the other system outputs valid RS-232 sig-
nal transitions within that time, the RS-232 ports on both
systems remain enabled.
VLLogic Supply Input
Unlike other RS-232 interface devices where the receiv-
er outputs swing between 0V and VCC, the MAX3387E
features a separate logic supply input (VL) that sets
VOH for the receiver outputs and sets thresholds for the
receiver inputs. This feature allows a great deal of flexi-
bility in interfacing to many different types of systems
with different logic levels. Connect this input to the host
logic supply (1.8V ≤VL≤VCC). Also, see the
Typical
PDA/Cell-Phone Application
section.
POWERDOWN
AUTOSHDN
FORCEOFF
FORCEON
POWERDOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE
OPERATIONAL STATUS OF THE TRANSMITTERS AND THE POWER SUPPLIES.
Figure 2c. AutoShutdown Plus Logic
RECEIVER INPUT LEVELS
-2.7V
-0.3V
+2.7V
+0.3V
0V
INDETERMINATE
TRANSMITTERS ENABLED, INVALID HIGH
AutoShutdown, TRANSMITTERS DISABLED,
1μA SUPPLY CURRENT, INVALID LOW
TRANSMITTERS ENABLED, INVALID HIGH
INDETERMINATE
Figure 3a. Receiver Thresholds for INVALID
AUTOSHDN
R_IN
T_IN
R
S
30s
TIMER
EDGE
DETECT
EDGE
DETECT
FORCEOFF
FORCEON
Figure 2d. Power-Down Logic
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
_______________________________________________________________________________________ 9
VCC
0
V+
V-
VCC
0
INVALID
OUTPUT
TRANSMITTER
INPUTS
RECEIVER
INPUTS }INVALID
REGION
TRANSMITTER
OUTPUTS
tAUTOSHDN tWU tWU
tINVL tINVH tAUTOSHDN
Figure 3b. AutoShutdown Plus/INVALID Timing Diagram
Software-Controlled Shutdown
If direct software control is desired, INVALID can be
used to indicate a DTR or ring indicator signal. Connect
FORCEOFF and FORCEON together to bypass
AutoShutdown so the line acts like a SHDN input.
±15kV ESD Protection
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against electro-
static discharges (ESDs) encountered during handling
and assembly. The MAX3387E driver outputs and
receiver inputs have extra protection against static
electricity. Maxim has developed state-of-the-art struc-
tures to protect these pins against ESD of ±15kV with-
out damage. The ESD structures withstand high ESD in
all states: normal operation, shutdown, and powered
down. After an ESD event, Maxim’s “E” version devices
keep working without latchup, whereas competing RS-
232 products can latch and must be powered down to
remove latchup. ESD protection can be tested in vari-
ous ways. The transmitter outputs and receiver inputs
of this product family are characterized for protection to
the following limits:
1) ±15kV using the Human Body Model
2) ±8kV using the Contact-Discharge method specified
in IEC 1000-4-2
3) ±15kV using IEC 1000-4-2’s Air-Gap method
FORCEON
MASTER SHDN LINE
0.1μF1M
FORCEOFF
MAX3387E
POWER-
MANAGEMENT
UNIT
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a
System
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
10 ______________________________________________________________________________________
ESD Test Conditions
ESD performance depends on a variety of conditions.
Contact Maxim for a reliability report that documents
test setup, methodology, and results.
Human Body Model
Figure 5a shows the Human Body Model, and Figure
5b shows the current waveform it generates when dis-
charged into a low impedance. This model consists of a
100pF capacitor charged to the ESD voltage of interest,
which is then discharged into the test device through a
1.5kΩresistor.
Table 1. Output Control Truth Table
OPERATION STATUS FORCEON FORCEOFF
VALID
RECEIVER
LEVEL
RECEIVER OR
TRANSMITTER
EDGE WITHIN
30
T_OUT R_OUT
Shutdown
(Forced Off) X 0 X X High-Z Active
Normal Operation
(Forced On) 1 1 X X Active Active
Normal Operation
(AutoShutdown Plus) 0 1 X Yes Active Active
Shutdown
(AutoShutdown Plus) 0 1 X No High-Z Active
Normal Operation INVALID 1Yes XActive Active
Normal Operation INVALID 1 X Yes Active Active
Shutdown INVALID 1No No High-Z Active
Normal Operation
(AutoShutdown) INVALID INVALID Yes XActive Active
Shutdown
(AutoShutdown) INVALID INVALID No XHigh-Z Active
CHARGE-CURRENT
LIMIT RESISTOR
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
Cs
100pF
RC
1M
RD
1500Ω
HIGH-
VOLTAGE
DC
SOURCE
DEVICE
UNDER
TEST
Figure 5a. Human Body ESD Test Model
IP 100%
90%
36.8%
tRL TIME
tDL
CURRENT WAVEFORM
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
Ir
10%
0
0
AMPERES
Figure 5b. Human Body Current Waveform
X = Don’t care
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
______________________________________________________________________________________ 11
IEC 1000-4-2
The IEC 1000-4-2 standard covers ESD testing and
performance of finished equipment; it does not specifi-
cally refer to ICs. The MAX3387E helps you design
equipment that meets Level 4 (the highest level) of IEC
1000-4-2, without the need for additional ESD-protec-
tion components.
The major difference between tests done using the
Human Body Model and IEC 1000-4-2 is higher peak
current in IEC 1000-4-2 because series resistance is
lower in the IEC 1000-4-2 model. Hence, the ESD with-
stand voltage measured to IEC 1000-4-2 is generally
lower than that measured using the Human Body
Model. Figure 6a shows the IEC 1000-4-2 model, and
Figure 6b shows the current waveform for the ±8kV IEC
1000-4-2 Level 4 ESD Contact Discharge test.
The air-gap test involves approaching the device with a
charged probe. The contact-discharge method connects
the probe to the device before the probe is energized.
Machine Model
The Machine Model for ESD tests all pins using a
200pF storage capacitor and zero discharge resis-
tance. Its objective is to emulate the stress caused by
contact that occurs with handling and assembly during
manufacturing. All pins require this protection during
manufacturing, not just RS-232 inputs and outputs.
Therefore, after PC board assembly, the Machine
Model is less relevant to I/O ports.
Applications Information
Capacitor Selection
The capacitor type used for C1–C4 is not critical for
proper operation; polarized or nonpolarized capacitors
can be used. The charge pump requires 0.1µF capaci-
tors for 3.3V operation. For other supply voltages, see
Table 2 for required capacitor values. Do not use val-
ues smaller than those listed in Table 2. Increasing the
capacitor values (e.g., by a factor of 2) reduces ripple
on the transmitter outputs and slightly reduces power
consumption. C2, C3, and C4 can be increased without
changing C1’s value. However, do not increase C1
without also increasing the values of C2, C3, and C4 to
maintain the proper ratios (C1 to the other capacitors).
When using the minimum required capacitor values,
make sure the capacitor value does not degrade
excessively with temperature. If in doubt, use capaci-
tors with a larger nominal value. The capacitor’s equiva-
lent series resistance (ESR), which usually rises at low
temperatures, influences the amount of ripple on V+
and V-.
CHARGE-CURRENT
LIMIT RESISTOR
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
Cs
150pF
RC
50M to 100M
RD
330Ω
HIGH-
VOLTAGE
DC
SOURCE
DEVICE
UNDER
TEST
Figure 6a. IEC 1000-4-2 ESD Test Model
tR = 0.7ns to 1ns
30ns
60ns
t
100%
90%
10%
IPEAK
I
Figure 6b. IEC 1000-4-2 ESD Generator Current Waveform
Table 2. Minimum Required Capacitor
Values
VCC
(V)
0.10.1
C2, C3, C4
(µF)
3.0 to 3.6
0.330.047
10.223.0 to 5.5
4.5 to 5.5
C1
(µF)
MAX3387E
Power-Supply Decoupling
In most circumstances, a 0.1µF bypass capacitor is ade-
quate. In applications that are sensitive to power-supply
noise, decouple VCC to ground with a capacitor of the
same value as charge-pump capacitor C1. Connect
bypass capacitors as close to the IC as possible.
Operation Down to 2.7V
Transmitter outputs will meet TIA/EIA-562 levels of
±3.7V with supply voltages as low as +2.7V.
Transmitter Outputs when
Exiting Shutdown
Figure 7 shows two transmitter outputs when exiting
shutdown mode. As they become active, the two trans-
mitter outputs are shown going to opposite RS-232 lev-
els (one transmitter input is high; the other is low). Each
transmitter is loaded with 3kΩin parallel with 2500pF.
The transmitter outputs display no ringing or undesir-
able transients as they come out of shutdown. Note that
the transmitters are enabled only when the magnitude
of V- exceeds approximately 3V.
High Data Rates
The MAX3387E maintains the RS-232 ±5.0V minimum
transmitter output voltage even at high data rates.
Figure 8 shows a transmitter loopback test circuit.
Figure 9 shows a loopback test result at 120kbps, and
Figure 10 shows the same test at 250kbps. For Figure
9, all transmitters were driven simultaneously at
120kbps into RS-232 loads in parallel with 1000pF. For
Figure 10, a single transmitter was driven at 250kbps,
and all transmitters were loaded with an RS-232 receiv-
er in parallel with 1000pF.
Interconnection with
3V and 5V Logic
The MAX3387E can directly interface with various 5V
logic families, including ACT and HCT CMOS. The logic
voltage power-supply pin (VL) sets the output voltage
level of the receivers and the input thresholds of the
transmitters.
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
12 ______________________________________________________________________________________
MAX3387E
5k
R_ IN
R_ OUT
C2-
C2+
C1-
C1+
V-
V+
VCC
C4
C3
C1
C2
0.1μF
VCC
FORCEON
FORCEOFF
T_ OUT
T_ IN
GND
VCC
1000pF
Figure 8. Loopback Test Circuit
2μs/div
T1IN
T1OUT
R1OUT
5V/div
5V/div
5V/div
VCC = 3.3V
Figure 9. Loopback Test Results at 120kbps
50μs/div
T2
T1
5V/div
2V/div
VCC = 3.3V
C1–C4 = 0.1μF
Figure 7. Transmitter Outputs when Exiting Shutdown
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
______________________________________________________________________________________ 13
Typical PDA/Cell-Phone Application
The MAX3387E is designed with PDA applications in
mind. Two transmitters and two receivers handle stan-
dard full-duplex communication protocol, while an extra
transmitter allows a ring indicator signal to alert the
UART on the PC. Without the ring indicator transmitter,
solutions for these applications would require software-
intensive polling of the cradle inputs.
The ring indicate (RI) signal is generated when a PDA,
phone, or other “cradled” device is plugged into its cradle.
This generates a logic-low signal to the RI transmitter
input, creating +6V at the ring indicate pin. The PC’s
UART RI input is the only pin that can generate an inter-
rupt from signals arriving through the RS-232 port. The
interrupt routine for this UART will then service the RS-
232 full-duplex communication between the PDA and
the PC.
As cell phone design becomes more like that of PDAs,
cell phones will require similar docking ability and com-
munication protocol. Cell phones operate on a single
lithium-ion (Li+) battery and work with a power-supply
voltage of +2.7V to +4V. The baseband logic coming
from the phone connector can be as low as 1.8V at the
transceivers. To prevent forward biasing of a device
internal to the cell phone, the MAX3387E comes with a
logic power-supply pin (VL) that limits the logic levels
presented to the phone. The receiver outputs will sink
to zero for low outputs, but will not exceed VLfor logic
highs. The input logic levels for the transmitters are also
altered, scaled by the magnitude of the VLinput. The
device will work with VLas low as 1.8V before the
charge-pump noise will begin to cause the transmitter
outputs to oscillate. This is useful with cell phones and
other power-efficient devices with core logic voltage
levels that go as low as 1.8V.
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns,
go to www.maxim-ic.com/packages. Note that a “+”, “#”, or
“-” in the package code indicates RoHS status only. Package
drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
2μs/div
T1IN
T1OUT
R1OUT
5V/div
5V/div
5V/div
VCC = 3.3V
Figure 10. Loopback Test Results at 250kbps
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
24 TSSOP U24+1 21-0066
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
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.
14
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
Added Note 2 to the Electrical Characteristics table 4
3 6/10
Changed the Chip Information section to say “PROCESS: BiCMOS” 13
