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MAX3238CAI+ |MAX3238CAIMAXIMN/a8avai+3.0V to +5.5V, 1µA, Up to 250kbps, True RS-232 Transceiver with AutoShutdown Plus
MAX3238CAI+T |MAX3238CAITMAXIMN/a1750avai+3.0V to +5.5V, 1µA, Up to 250kbps, True RS-232 Transceiver with AutoShutdown Plus
MAX3238CAI+T |MAX3238CAITMAXN/a1034avai+3.0V to +5.5V, 1µA, Up to 250kbps, True RS-232 Transceiver with AutoShutdown Plus


MAX3238CAI+T ,+3.0V to +5.5V, 1µA, Up to 250kbps, True RS-232 Transceiver with AutoShutdown PlusFeaturesThe MAX3238 true RS-232 transceiver achieves a ♦ 1µA Supply Current Achieved with 1µA suppl ..
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MAX3238CAI+-MAX3238CAI+T
+3.0V to +5.5V, 1µA, Up to 250kbps, True RS-232 Transceiver with AutoShutdown Plus
_______________General Description
The MAX3238 true RS-232 transceiver achieves a
1µA supply current with Maxim’s revolutionary
AutoShutdown Plus™ feature. When the device does
not sense a valid signal transition on either the receiver
or transmitter inputs within 30sec, the on-board power
supply and drivers shut down. This occurs if the RS-232
cable is disconnected or if the transmitters of the con-
nected peripheral are inactive. The system turns on
again when a valid transition is applied to any RS-232
receiver or transmitter input, saving power without
changes to the existing BIOS or operating system.
The MAX3238 5-driver/3-receiver complete serial port is
a 3V-powered EIA/TIA-232 and V.28/V.24 communica-
tions interface intended for notebook or subnotebook
computer applications. A proprietary, high-efficiency,
dual charge-pump power supply and a low-dropout
transmitter combine to deliver true RS-232 performance
from a single +3.0V to +5.5V supply. A guaranteed
data rate of 250kbps provides compatibility with popu-
lar software for communicating with personal comput-
ers. The MAX3238 requires only 0.1µF capacitors in
3.3V operation. It is ideal for 3.3V-only systems, mixed
3.3V and 5.0V systems, or 5V-only systems that require
true RS-232 performance.
Receiver R1 has an extra, always-active output (in addi-
tion to its standard output), which allows external
devices, such as a modem, to be monitored without for-
ward biasing the protection diodes in circuitry that may
have VCCcompletely removed.
The MAX3238 is available in a space-saving SSOP
package.
________________________Applications

Notebook, Subnotebook, and Palmtop
Computers
High-Speed Modems
Battery-Powered Equipment
Hand-Held Equipment
Peripherals
Printers
AutoShutdown Plus is a trademark of Maxim Integrated Products.
____________________________Features
1µA Supply Current Achieved with
AutoShutdown Plus
Guaranteed Data Rate: 250kbps 1µA Low-Power ShutdownReceivers Active in AutoShutdown Plus ModeFlow-Through Pinout Meets EIA/TIA-232 Specifications Down to 3.0VGuaranteed 6V/µs Slew Rate
MAX3238
+3.0V to +5.5V, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus

C1+
VCC
C1-
T1IN
T2IN
INVALID
T3IN
R1OUT
R2OUT
T4IN
R3OUT
T5IN
R1OUTB
FORCEOFF
FORCEON
T5OUT
R3IN
T4OUT
R2IN
R1IN
T3OUT
T2OUT
T1OUT
C2-
GND
C2+
SSOP

TOP VIEW
MAX3238
__________________Pin Configuration

19-1144; Rev 1; 10/02
PART

MAX3238CAI
MAX3238EAI-40°C to +85°C
0°C to +70°C
TEMP RANGEPIN-PACKAGE

28 SSOP
28 SSOP
______________Ordering Information
Typical Operating Circuit appears at end of data sheet.
MAX3238
+3.0V to +5.5V, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS

(VCC= +3.0V to +5.5V; C1–C4 = 0.1µF (tested at 3.3V ±5%), C1–C4 = 0.22µF (tested at 3.3V ±10%), C1 = 0.047µF and
C2–C4 = 0.33µF (tested at 5.0V ±10%); TA= TMINto TMAX; unless otherwise noted. Typical values are at 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.
VCC...........................................................................-0.3V to +6V
V+ (Note 1)...............................................................-0.3V to +7V
V- (Note 1)................................................................+0.3V to -7V
V+ + |V-| (Note 1).................................................................+13V
Input Voltages
T_IN, FORCEOFF, FORCEON..............................-0.3V to +6V
R_IN.................................................................................±25V
Output Voltages
T_OUT...........................................................................±13.2V
R_OUT, INVALID....................................-0.3V to (VCC+ 0.3V)
Short-Circuit Duration
T_OUT (one at a time)............................................Continuous
Continuous Power Dissipation (TA= +70°C)
SSOP (derate 9.52mW/°C above +70°C)....................762mW
Operating Temperature Ranges
MAX3238CAI......................................................0°C to +70°C
MAX3238EAI....................................................-40°C to +85°C
Storage Temperature Range ............................-65°C to +160°C
Lead Temperature (soldering, 10s) ................................+300°C
FORCEOFF= GND, TA= +25°C
VCC= 3.3V or 5.0V, TA= +25°C, receivers idle,
transmitters idle, FORCEON = GND,
FORCEOFF= VCC
IOUT= -1.0mA
IOUT= 1.6mA
Receivers disabled
T_IN, FORCEON, FORCEOFF
FORCEON = FORCEOFF= VCC, no load
T_IN, FORCEON, FORCEOFF
VCC= 3.3V
CONDITIONS
1.010Supply Current, Shutdown1.010Supply Current, AutoShutdown PlusVCC -VCC -
0.60.1Output Voltage High0.4Output Voltage Low±0.05±10Output Leakage Current±0.01±1.0Input Leakage Current0.52.0Supply Current, AutoShutdown Plus
Disabled0.8Input Logic Threshold Low2.0Input Logic Threshold High
UNITSMINTYPMAXPARAMETER
Note 1:
V+ and V- can have a maximum magnitude of +7V, but their absolute difference can not exceed +13V.
VCC= 5.0V2.4-2525Input Voltage Range
VCC= 3.3V0.61.2
VCC= 5.0VV0.81.5Input Threshold Low
VCC= 3.3V1.52.4
VCC= 5.0VV1.82.4Input Threshold High0.3Input Hysteresis= +25°CkΩ357Input Resistance
DC CHARACTERISTICS
LOGIC INPUTS AND RECEIVER OUTPUTS
RECEIVER INPUTS
MAX3238
+3.0V to +5.5V, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus
ELECTRICAL CHARACTERISTICS (continued)

(VCC= +3.0V to +5.5V; C1–C4 = 0.1µF (tested at 3.3V ±5%), C1–C4 = 0.22µF (tested at 3.3V ±10%), C1 = 0.047µF and
C2–C4 = 0.33µF (tested at 5.0V ±10%); TA= TMINto TMAX; unless otherwise noted. Typical values are at TA= +25°C.)
Figure 4a
Figure 7a
Figure 4b (Note 2)
VCC= 5V, Figure 4b (Note 2)
VCC= 5V, Figure 4b
IOUT= 1.6mA
IOUT= -1.0mA
VCC= 5V, Figure 4b
CONDITIONS
-0.30.3Receiver Input Threshold to
INVALIDOutput Low
2.7Receiver Input Threshold to
INVALIDOutput High
sec153060Receiver or Transmitter Edge to
Shutdown (tAUTOSHDN)25Receiver or Transmitter Edge to
Transmitters Enabled (tWU)50Receiver Positive or Negative
Threshold to INVALIDLow (tINVL)0.4INVALIDOutput Voltage LowVCC -
0.6INVALIDOutput Voltage High0.1Receiver Positive or Negative
Threshold to INVALIDHigh (tINVH)
UNITSMINTYPMAXPARAMETER

Positive threshold
Negative threshold-2.7
Output Voltage SwingAll transmitter outputs loaded with 3kΩto ground±5.0±5.4V
Output ResistanceVCC= V+ = V- = GND, TOUT= 2V30010MΩ
VCC≤3.6V±35±60
Output Leakage CurrentVOUT= ±12V, VCC= 0V to 5.5V,
transmitters disabled±25µA
| tPHL- tPLH|
tPHLR_IN to R_OUT,= 150pFtPLH= 150pF to 1000pF= 3kΩ, CL= 1000pF, one transmitter switching= 150pF to 2500pF
VCC= 3.3V,= +25°C, = 3Ωto 7kΩ,
measured from +3V to
-3V or -3V to +3V
Normal operation
Normal operation
| tPHL- tPLH|0.15Receiver Propagation Delay
kbps250Maximum Data Rate
V/µs
Transition-Region Slew Rate200Receiver Output Enable Time200Receiver Output Disable Time100Transmitter Skew50Receiver Skew
TIMING CHARACTERISTICS

Output Short-Circuit CurrentVCC> 3.6V±40±100
AutoShutdown
(FORCEON = GND, FORCEOFF= VCC)
TRANSMITTER OUTPUTS
Note 2:
A transmitter/receiver edge is defined as a transition through the transmitter/receiver input logic thresholds.
______________________________________________________________Pin Description
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE
MAX3238 TOC-01
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
VOUT+
VOUT–
FOR DATA RATES UP TO 250kbps
1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
LOADED 3kΩ + CL100030005000
SLEW RATE
vs. LOAD CAPACITANCE

MAX3238-02
SLEW RATE (V/
LOAD CAPACITANCE (pF)
+SLEW
–SLEW
1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
LOADED 3kΩ + CL100030005000
SUPPLY CURRENT vs. LOAD CAPACITANCE
WHEN TRANSMITTING DATA

MAX3238 TOC-03
SUPPLY CURRENT (mA)
LOAD CAPACITANCE (pF)
250kbps
120kbps
20kbps
__________________________________________Typical Operating Characteristics

(VCC= +3.3V, 250kbps data rate, 0.1µF capacitors, all transmitters loaded with 3kΩ, TA= +25°C, unless otherwise noted.)
MAX3238
+3.0V to +5.5V, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus

Positive Terminal of Voltage-Doubler Charge-Pump CapacitorC1+28
+5.5V Generated by the Charge PumpV+27
+3.0V to +5.5V Supply VoltageVCC26
NAMEFUNCTION
C2+Positive Terminal of Inverting Charge-Pump CapacitorGNDGround
PIN
C2-Negative Terminal of Inverting Charge-Pump CapacitorV--5.5V Generated by the Charge PumpFORCEOFFForce-Off Input. Drive low to shut down transmitters, receivers (except R1OUTB), and on-
board supply. This overrides AutoShutdown Plus and FORCEON (Table 1).FORCEONForce-Off Input. Drive high to override AutoShutdown Plus, keeping transmitters and
receivers on (FORCEOFFmust be high) (Table 1).
8, 9, 11R_INRS-232 Receiver Inputs (R1IN–R3IN)
5, 6, 7, 10, 12T_OUTRS-232 Transmitter Outputs (T1OUT–T5OUT)C1-Negative Terminal of Voltage-Doubler Charge-Pump Capacitor
18, 20, 21R_OUTTTL/CMOS Receiver Outputs (R3OUT–R1OUT)
17, 19, 22, 23, 24T_INTTL/CMOS Transmitter Inputs (T5IN–T1IN)R1OUTBNoninverting Complementary Receiver Output. Always active.INVALIDOutput of the Valid Signal Detector. A logic “1” indicates if a valid RS-232 level is present
on receiver inputs.
MAX3238
+3.0V to +5.5V, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus
_______________Detailed Description
Dual Charge-Pump Voltage Converter

The MAX3238’s internal power supply consists of a reg-
ulated dual charge pump that provides output voltages
of +5.5V (doubling charge pump) and -5.5V (inverting
charge pump), regardless of the input voltage (VCC)
over the 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 flying 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
MAX3238 transmitters guarantee a 250kbps data rate
with worst-case loads of 3kΩin parallel with 1000pF,
providing compatibility with PC-to-PC communication
software (such as LapLink™). Transmitters can be par-
alleled to drive multiple receivers. Figure 1 shows a
complete system connection.
LapLink is a trademark of Traveling Software.
When FORCEOFFis driven to ground, the transmitters
and receivers are disabled and the outputs go high
impedance, except for R1OUTB. When the Auto-
Shutdown Plus circuitry senses that all receiver and
transmitter inputs are inactive for more than 30sec, the
transmitters are disabled and the outputs go into a
high-impedance state, but the receivers remain active.
When the power is off, the MAX3238 permits the out-
puts to be driven up to ±12V.
The transmitter inputs do not have pull-up resistors.
Connect unused inputs to GND or VCC.
RS-232 Receivers

The receivers convert RS-232 signals to CMOS-logic
output levels. All receivers have inverting three-state
outputs and are inactive in shutdown (FORCEOFF)
(Table 1). The MAX3238 also features an extra, always-
active noninverting output, R1OUTB. This extra output
monitors receiver activity while the other receivers are
high impedance, allowing Ring Indicator to be moni-
tored without forward biasing other devices connected
to the receiver outputs. This is ideal for systems where
VCCis set to 0V in shutdown to accommodate peripher-
als, such as UARTs (Figure 2).
Table 1. Output Control Truth Table
FORCEON
FFOORRCCEEOOFFFFAUTOSHUTDOWN
PLUS*
OPERATION
STATUST_OUTR_OUTR1OUTB
0XShutdown
(Forced Off)High-ZHigh-ZActive1XNormal Operation
(Forced On)ActiveActiveActive1<30sec*
Normal
Operation
(AutoShutdown
Plus)
ActiveActiveActive1>30sec*
Shutdown
(AutoShutdown
Plus)
High-ZActiveActive= Don’t Care
*Time since last receiver or transmitter input transition.
MAX3238
+3.0V to +5.5V, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus
AutoShutdown Plus Mode

1µA supply current is achieved with Maxim’s
AutoShutdown Plus feature, which operates when
FORCEOFFis high and FORCEON is low. When the
MAX3238 senses no valid signal transitions on all
receiver and transmitter inputs for 30sec, the on-board
power supply and drivers are shut off, reducing supply
current to 1µA. This occurs if the RS-232 cable is dis-
connected or if the connected peripheral transmitters
are turned off. The system turns on again when a valid
transition is applied to any RS-232 receiver or transmit-
ter input. As a result, the system saves power without
changes to the existing BIOS or operating system. The
INVALIDoutput is high when the receivers are active.
Since INVALIDindicates the receiver inputs’ condition,
it can be used in any mode (Figure 3).
MAX3238
I/O
CHIP
WITH
UART
CPU
RS-232
POWER
MANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
FORCEOFF
FORCEON
INVALID
Figure 1. Interface Under Control of PMU
MAX3238
T1OUT
R1OUTB
5kΩUART
VCC
T1IN
THREE-STATED
LOGIC
TRANSITION
DETECTOR
R1IN
PROTECTION
DIODE
R1OUT
FORCEOFF = GND
VCC
PREVIOUS
RS-232
UART
SHDN = GND
VCC
VCC
GND
5kΩ
(a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE

RECEIVER OUTPUT IN SHUTDOWN.
(b) NEW MAX3238: IN SHUTDOWN, R1OUTB IS USED TO MONITOR EXTERNAL

DEVICES AND R1OUT IS THREE STATED, ELIMINATING A CURRENT PATH
THROUGH THE UART'S PROTECTION DIODE.
GND
PROTECTION
DIODE
Figure 2. The MAX3238 detects RS-232 activity when the
UART and interface are shut down.
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