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MAX3238EAI+ |MAX3238EAIMAXN/a22avai+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pins
MAX3238EAI+T |MAX3238EAITMAXIM N/a4000avai+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pins
MAX3238ECAI+ |MAX3238ECAIMAXN/a80avai+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pins
MAX3238ECAI+T |MAX3238ECAITMAXIMN/a1368avai+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pins
MAX3238EEAI+ |MAX3238EEAIMAXN/a65avai+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pins
MAX3238EEAI+TMAXIMN/a5000avai+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pins
MAX3248EEAI+ |MAX3248EEAIMAXIMN/a8avai+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pins


MAX3238EEAI+T ,+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic PinsELECTRICAL CHARACTERISTICS(V = +3.0V to +5.5V, C1–C4 = 0.1µF (tested at 3.3V ±5%), C1–C4 = 0.22µF ( ..
MAX3238EIDBR ,3-V to 5.5-V Multichannel RS-232 Line Driver/Receiver With +/-15-kV ESD (HBM) Protection 28-SSOP -40 to 85SLLS710A–FEBRUARY 2006–REVISED APRIL 2006DESCRIPTION/ORDERING INFORMATION (CONTINUED)Flexible contr ..
MAX3238EIPW ,3-V to 5.5-V Multichannel RS-232 Line Driver/Receiver With +/-15-kV ESD (HBM) Protection 28-TSSOP -40 to 85SLLS710A–FEBRUARY 2006–REVISED APRIL 2006FUNCTION TABLESabc(1)Each DriverINPUTSOUTPUTDRIVER STATUST ..
MAX3238EIPWG4 ,3-V to 5.5-V Multichannel RS-232 Line Driver/Receiver With +/-15-kV ESD (HBM) Protection 28-TSSOP -40 to 85/sc/package.2Submit Documentation FeedbackMAX3238E3-V TO 5.5-V MULTICHANNEL RS-232 LINE DRIVER/RECE ..
MAX3238IDB ,3-V to 5.5-V Multichannel RS-232 Line Driver/Receiver/sc/package.Please be aware that an important notice concerning availability, standard warranty, an ..
MAX3238IDBR ,3-V to 5.5-V Multichannel RS-232 Line Driver/Receiver        ±      SLLS349J − ..
MAX6776LTA+T ,Low-Power, 1%-Accurate Battery Monitor in µDFN and SC70 PackagesELECTRICAL CHARACTERISTICS(V = 1.6V to 5.5V, T = -40°C to +85°C, unless otherwise specified. Typica ..
MAX6776XKA+T ,Low-Power, 1%-Accurate Battery Monitor in µDFN and SC70 PackagesApplicationsBattery-Powered Systems (Single-Cell Li+ orMulticell NiMH, NiCd, Alkaline)Cell Phones/C ..
MAX6777XK+ ,Low-Power, 1%-Accurate Battery Monitor in µDFN and SC70 PackagesELECTRICAL CHARACTERISTICS (continued)(V = 1.6V to 5.5V, T = -40°C to +85°C, unless otherwise speci ..
MAX677ACPP ,V(cc): -0.3 to +20V; calibrated, low-drift, +4.096V / +5V / +10V precision voltage reference. For high resolution 16-bit ADCs and DACs, precision test and measurement systems, precision calibrated voltage-reference, high-accuracy transduceELECTRICAL CHARACTERISTICS-MAF (Vcc = +5V, IL = 0mA, TA = +25 tl unless otherWIse noted.) MAX ..
MAX677BCPP ,889mW; V(cc): -0.3 to +20V; calibrated, low-drift, +4.096V / +5V / +10V precision voltage reference. For high resolution 16-bit ADCs and DACs, precision test and measurement systems, precision calibrated voltage-reference, high-accuracy trFeatures . Lowest Temperature Drift: 1ppml°c Max Over -40°c to +85°C I.5pprnf'C Max Over -55 ..
MAX6780LTA+T ,Low-Power, 1%-Accurate Battery Monitor in µDFN and SC70 PackagesFeaturesThe MAX6775–MAX6781 low-power, 1%-accurate bat- ♦ 1.0%-Accurate Threshold Specified Overter ..


MAX3238EAI+-MAX3238EAI+T-MAX3238ECAI+-MAX3238ECAI+T-MAX3238EEAI+-MAX3238EEAI+T-MAX3248EEAI+
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pins
General Description
The MAX3238E/MAX3248E transceivers use Maxim’s
revolutionary AutoShutdown Plus™ feature to achieve
10nA supply current. These devices shut down the on-
board power supply and drivers when they do not sense
a valid signal transition on either the receiver or transmit-
ter inputs. This occurs if the RS-232 cable is disconnect-
ed or if the transmitters of the connected peripheral are
turned off. The devices turn on again when a valid transi-
tion is applied to any RS-232 receiver or transmitter input.
AutoShutdown Plus automatically achieves this power
savings through its on-board circuitry, as no changes are
required to the existing BIOS or operating system.
All RS-232 inputs and outputs, as well as the logic I/O
pins, have enhanced ESD protection to ±15kV. The addi-
tional ESD protection on the logic I/O pins makes the
MAX3238E/MAX3248E ideal for cell phone data cable
applications because it eliminates the need for costly
external TransZorb™or protection schemes.
The MAX3238E/MAX3248E contain five drivers and three
receivers and are 3V-powered EIA/TIA-232 and V.28/V.24
communication interfaces intended for cell phones, data
cables, and modem applications. A proprietary, high-effi-
ciency, 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 popular software for communicating with personal
computers.
The MAX3238E and the MAX3248E differ only in their
input logic thresholds. The MAX3238E has standard logic
thresholds, while the MAX3248E has low-level logic
thresholds of 0.6V to 1.2V, which are ideal for 1.8V sys-
tems.
The transmitter inputs, FORCEON, and FORCEOFFhave
a 400kΩactive positive feedback resistor. Once driven to
a valid logic level, they will retain this level if the driving
signal is removed or goes high impedance. Unused
transmitter and logic inputs may be left unconnected. The
MAX3238E/MAX3248E can operate with supply voltages
ranging from +3.0V to +5.5V.
Applications
Features
Enhanced ESD Protection on RS-232 I/O Pins and
All Logic Pins
±15kV—Human Body Model
±8kV—IEC 1000-4-2 Contact Discharge
±15kV—IEC 1000-4-2 Air-Gap Discharge
Guaranteed Data Rate: 250kbps 10nA Low-Power Shutdown with Receivers ActiveSchmitt Triggers on All InputsFlow-Through PinoutMeets EIA/TIA-232 Specifications Down to 3.0VGuaranteed 6V/µs Slew RateLow-Level Logic Thresholds (MAX3248E)RS-232-Compatible Outputs to 2.7V
MAX3238E/MAX3248E
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins

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+
TOP VIEW
MAX3238E
MAX3248E
___________________Pin Configuration

19-1632; Rev 1; 6/01
Ordering Information

AutoShutdown Plus is a trademark of Maxim Integrated Products.
TransZorb is a trademark of General Semiconductor Industries, Inc.
†C4;
4,r
Cellular Data Cables
Modems
Battery-Powered Equipment
Peripherals
Data Cradles
Printers
Typical Operating Circuit appears at end of data sheet.

28 SSOP
28 SSOP
28 SSOP
28 SSOP
PIN-PACKAGETEMP. RANGE

0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°CMAX3248EEAI
MAX3248ECAI

MAX3238EEAI
MAX3238ECAI
PART
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.
MAX3238E/MAX3248E
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
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.)
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)
28-Pin SSOP (derate 9.52mW/°C above +70°C).........762mW
Operating Temperature Ranges
MAX3238ECAI/MAX3248ECAI...........................0°C to +70°C
MAX3238EEAI/MAX3248EEAI.........................-40°C to +85°C
Storage Temperature Range ............................-65°C to +150°C
Lead Temperature (soldering, 10s) ................................+300°C
Note 1:
V+ and V- can have a maximum magnitude of +7V, but their absolute difference can not exceed +13V.
0.951.2MAX3248E
FORCEON, FORCEOFF,and T_IN
FORCEON, FORCEOFF,and T_IN
wake-up threshold; VCC= 3.3V
T_IN (active)
FORCEON, FORCEOFF,and T_IN
wake-up threshold; VCC= 5.0V
FORCEON, FORCEOFF,and T_IN
wake-up threshold; VCC= 3.3V
T_IN (active)
FORCEON, FORCEOFF,and T_IN
wake-up threshold; VCC= 5.0V
FORCEON, FORCEOFF,and T_IN
wake-up threshold; VCC= 3.3V
T_IN (active)
FORCEON, FORCEOFF,and T_IN
wake-up threshold; VCC= 5.0V
FORCEON, FORCEOFF,and T_IN
wake-up threshold; VCC= 3.3V
T_IN (active)
PARAMETERMINTYPMAXUNITS

Input Logic Threshold Low
Supply Current, AutoShutdown Plus
Disabled0.52.0mA
Supply Current, AutoShutdown Plus
Input Logic Threshold High
0.756µA300
1.302.0MAX3238E
MAX3248E
Supply Current, Shutdown10300nA
CONDITIONS

FORCEOFF= GND, R_IN = GND, T_IN = VCCor GND
MAX3238E
FORCEON = FORCEOFF= VCC, no load
Receivers idle, T_IN = VCCor GND, FORCEON =
GND, FORCEOFF= VCC
R_IN = FORCEON = GND, FORCEOFF = VCC,
T_IN = VCCor GNDnA
DC CHARACTERISTICS (VCC
= +3.3V or +5.0V, TA= +25°C)
LOGIC INPUTS AND RECEIVER OUTPUTS
MAX3238E/MAX3248E
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
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 4a
Figure 4b
VCC= 5V, Figure 4b (Note 3)
VCC= 5V, Figure 4b
IOUT= 1.0mA
IOUT= -1.0mA
VCC= 5V, Figure 4b-0.30.3Receiver Input Threshold to
INVALIDOutput Low2.7Receiver Input Threshold to
INVALIDOutput High153060Receiver or Transmitter Edge to
Shutdown (tAUTOSHDN)25Receiver or Transmitter Edge to
Transmitters Enabled (tWU)60Receiver Positive or Negative
Threshold to INVALIDLow (tINVL)0.4INVALIDOutput Voltage LowVCC -
0.6INVALIDOutput Voltage High0.3Receiver Positive or Negative
Threshold to INVALIDHigh (tINVH)
Positive threshold
Negative threshold-2.7-2525
IOUT= -1.0mA
IOUT= 1.0mA
Input Voltage Range
VCC= 3.3V
Receivers disabled
T_IN, FORCEON, FORCEOFF(Note 2)
CONDITIONS
VCC= 5.0VV0.81.4Input Threshold Low
VCC= 3.3V1.52.4
VCC= 5.0VV2.02.4Input Threshold High0.6Input Hysteresis= +25°CkΩ357Input ResistanceVCC -VCC -
0.60.1Output Voltage High0.4Output Voltage Low±0.05±10Output Leakage Current918Input Leakage Current
UNITSMINTYPMAXPARAMETER

All transmitter outputs loaded with 3kΩto groundV±5.0±5.4Output Voltage Swing
VCC= 0, TOUT= ±2VΩ30050kOutput Resistance
VCC≤3.6V±35±60
VCC> 3.6VmA±40±100Output Short-Circuit Current
IEC 1000-4-2 Air-Gap Discharge Method±15
IEC 1000-4-2 Contact Discharge Method±8
Human Body Model
±15
ESDProtection (R_IN, T_IN, R_OUT,
T_OUT,FORCEON, FORCEOFF,
INVALID, R_OUTB)
RECEIVER INPUTS
AutoShutdown
(FORCEON = GND, FORCEOFF= VCC)
TRANSMITTER OUTPUTS
ESD PROTECTION
10001500500200025003000TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE

MAX3238E toc01
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
VOUT-
VOUT+
FOR DATA RATES UP TO 250kbps
1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
WITH 3kΩ + CL10001500500200025003000
SLEW RATE vs. LOAD CAPACITANCE

MAX3238E toc02
LOAD CAPACITANCE (pF)
SLEW RATE (V/
SR+
SR-
1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
WITH 3kΩ + CL100050020003000
SUPPLY CURRENT vs. LOAD CAPACITANCE
WHEN TRANSMITTING DATA

MAX3238 TOC-03
SUPPLY CURRENT (mA)
LOAD CAPACITANCE (pF)
250kbps
20kbps
120kbps
1 TRANSMITTER 20kbps, 120 kbps, 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
WITH 3kΩ + CL
__________________________________________Typical Operating Characteristics

(VCC= +3.3V, 250kbps data rate, 0.1µF capacitors, all transmitters loaded with 3kΩ, TA= +25°C, unless otherwise noted.)
MAX3238E/MAX3248E
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
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.)
Note 2:
The transmitter inputs have an active positive feedback resistor. The input current goes to zero when the inputs are at the
supply rails.
Note 3:
During AutoShutdown only, a transmitter/receiver edge is defined as a transition through the transmitter/receiver input logic
wake-up thresholds.
CONDITIONSUNITSMINTYPMAXPARAMETER

| 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, = 3kΩto 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 Rate2.6Receiver Output Enable Time2.4Receiver Output Disable Time5050Receiver Skew
Transmitter Skew
TIMING CHARACTERISTICS
MAX3238E/MAX3248E
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
Typical Operating Characteristics (continued)

(VCC= +3.3V, 250kbps data rate, 0.1µF capacitors, all transmitters loaded with 3kΩ, TA= +25°C, unless otherwise noted.)
______________________________________________________________Pin Description

Output of the Valid Signal Detector. A logic 1 indicates if a valid RS-232 level is present on
receiver inputs.INVALID15
Noninverting Complementary Receiver Output. Always active.R1OUTB16
TTL/CMOS Transmitter Inputs (T5IN–T1IN). This pin has an active positive feedback resis-
tor. Once driven to a valid logic level, the pin retains that level if left unconnected until
power is cycled.
T_IN17, 19, 22, 23, 24
TTL/CMOS Receiver Outputs (R3OUT–R1OUT)R_OUT18, 20, 21
Negative Terminal of Voltage-Doubler Charge-Pump CapacitorC1-25
RS-232 Transmitter Outputs (T1OUT–T5OUT)T_OUT5, 6, 7, 10, 12
RS-232 Receiver Inputs (R1IN–R3IN)R_IN8, 9, 11
Force-On Input. Drive high to override AutoShutdown Plus, keeping transmitters and
receivers on (FORCEOFFmust be high) (Table 1). This pin has an active positive feedback
resistor. Once driven to a valid logic level, the pin retains that level if left unconnected until
power is cycled.
FORCEON13
Force-Off Input. Drive low to shut down transmitters, receivers (except R1OUTB), and on-
board supply. This overrides AutoShutdown Plus and FORCEON (Table 1). This pin has an
active positive feedback resistor. Once driven to a valid logic level, the pin retains that
level if left unconnected until power is cycled.
FORCEOFF14
-5.5V Generated by the Charge PumpV-4
Negative Terminal of Inverting Charge-Pump CapacitorC2-3
PIN

GroundGND2
Positive Terminal of Inverting Charge-Pump CapacitorC2+1
FUNCTIONNAME
VCC+3.0V to +5.5V Supply VoltageV++5.5V Generated by the Charge PumpC1+Positive Terminal of Voltage-Doubler Charge-Pump Capacitor
TRANSMITTER OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
MAX3238E toc04
SUPPLY VOLTAGE (V)
TRANSMITTER OUTPUT VOLTAGE (V)VOUT-
VOUT+
1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
WITH 3kΩ +1000pF
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX3238E toc05
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
WITH 3kΩ +1000pF
MAX3238E/MAX3248E
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
_______________Detailed Description
Dual Charge-Pump Voltage Converter

The MAX3238E/MAX3248Es’ internal power supply
consists of a regulated 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 fly-
ing capacitor (C1, C2) and a reservoir capacitor (C3,
C4) to generate the V+ and V- supplies.
RS-232 Transmitters

The MAX3248E transmitters are inverting level translators
that convert a logic low of 0.6V and logic high of 1.2V to
5.0V EIA/TIA-232 levels. The MAX3238E transmitters are
inverting level translators that convert CMOS-logic levels
to 5.0V EIA/TIA-232 levels. The MAX3238E/MAX3248E
transmitters both guarantee a 250kbps data rate with
worst-case loads of 3kΩin parallel with 1000pF, provid-
ing compatibility with PC-to-PC communication software
(such as LapLink™). Transmitters can be paralleled to
drive multiple receivers. Figure 1 shows a complete sys-
tem connection.
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 30s, the
transmitters are disabled and the outputs go into a
high-impedance state, but the receivers remain active.
When the power is off, the MAX3238E/MAX3248E per-
mit the outputs to be driven up to ±12V.
The transmitter inputs, FORCEON and FORCEOFF,
havea 400kΩactive positive-feedback resistor. Once
driven to a valid logic level, they will retain this level if
the driving signal is removed or goes high-impedance.
Unused transmitter inputs may be left unconnected.
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 MAX3238E/MAX3248Ealso feature 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 monitored without forward biasing other devices
connected to the receiver outputs. This is ideal for sys-
tems where VCCis set to 0 in shutdown to accommo-
date peripherals, such as UARTs (Figure 2).
Table 1. Output Control Truth Table
FORCEON
FORCEOFFAutoShutdown
Plus
OPERATION
STATUST_OUTR_OUTR1OUTB
0XShutdown
(Forced Off)High-ZHigh-ZActive1XNormal Operation
(Forced On)ActiveActiveActive1<30s*
Normal
Operation
(AutoShutdown
Plus)
ActiveActiveActive1>30s*
Shutdown
(AutoShutdown
Plus)
High-ZActiveActive
X = Don’t care
*Time since last receiver or transmitter input transition.
MAX3238E/MAX3248E
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
AutoShutdown Plus Mode

A 10nA supply current is achieved with Maxim’s
AutoShutdown Plus feature, which operates when
FORCEOFFis low and FORCEON is high. When the
MAX3238E/MAX3248E sense no valid signal transitions
on all receiver and transmitter inputs for 30s, the on-
board power supply and drivers are shut off, reducing
supply current to 1µA. If the receiver inputs are in the
invalid range (-0.3V < R_IN < +0.3V) and the transmit-
ter inputs are at GND or VCC, supply current is further
reduced to 10nA. This occurs if the RS-232 cable is
disconnected or if the connected peripheral transmit-
ters are turned off. 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. The INVALIDoutput is high when the receivers are
active. Since INVALIDindicates the receiver inputs’
condition, it can be used in any mode (Figure 3).
MAX3238E/
MAX3248E
I/O
CHIP
WITH
UART
CPU
RS-232
POWER
MANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
FORCEOFF
FORCEON
INVALID
Figure 1. Interface Under Control of PMU
MAX3238E
MAX3248E
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 MAX3238E/MAX3248E: 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. MAX3238E/MAX3248E detect RS-232 activity when
the UART and interface are shut down.
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