MAX3243CAI-T ,+3V to +5.5V RS-232 Transceivers with AutoShutdownApplicationsMAX3223EAP -40°C to +85°C 20 SSOP• Battery-Powered EquipmentMAX3223EUP -40°C to +85°C 2 ..
MAX3243CDB ,3-V to 5.5-V Multichannel RS-232 Line Driver/Receiver With +/-15kV ESD (HBM) ProtectionFeatures... 1 8 Parameter Measurement Information 82 Applications..... 1 9 Detailed Description.... ..
MAX3243CDBG4 ,3-V to 5.5-V Multichannel RS-232 Line Driver/Receiver With +/-15kV ESD (HBM) Protection 28-SSOP 0 to 70Block Diagram... 114 Simplified Diagram... 19.3 Feature Description.... 125 Revision History....... ..
MAX3243CDBR ,3-V to 5.5-V Multichannel RS-232 Line Driver/Receiver With +/-15kV ESD (HBM) Protectionfeatures saves power automatically. Specialoutputs ROUT2B and INVALID are always enabled to• Extern ..
MAX3243CDBRG4 ,3-V to 5.5-V Multichannel RS-232 Line Driver/Receiver With +/-15kV ESD (HBM) Protection 28-SSOP 0 to 70Electrical Characteristics –– Receiver ... 613.1 Trademarks..... 187.8 Switching Characteristics –– ..
MAX3243CDBRG4 ,3-V to 5.5-V Multichannel RS-232 Line Driver/Receiver With +/-15kV ESD (HBM) Protection 28-SSOP 0 to 70Maximum Ratings(1)over operating free-air temperature range (unless otherwise noted)MIN MAX UNIT(2) ..
MAX6823WUK+T ,Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog TimerElectrical Characteristics(V = +4.5V to +5.5V for MAX682_L/M, V = +2.7V to +3.6V for MAX682_T/S/R, ..
MAX6824LUK-T ,4.63 V, low-power mP supervisor with manual reset and watchdog timerMAX6821–MAX682519-1868; Rev 1; 1/01Low-Voltage SOT23 µP Supervisors withManual Reset and Watchdog T ..
MAX6825VUK-T ,1.58 V, low-power mP supervisor with manual reset and watchdog timerApplications MAX6824_UK-T -40°C to +125°C 5 SOT23-5 MAX6825 _UK-T -40°C to +125°C 5 SOT23-5 Set- ..
MAX6826LUT+ ,Dual, Ultra-Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog TimerMAX6826–MAX683119-1867; Rev 1; 1/02Dual Ultra-Low-Voltage SOT23 µP Supervisorswith Manual Reset and ..
MAX6826LUT+T ,Dual, Ultra-Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog TimerELECTRICAL CHARACTERISTICS(V = +4.5V to +5.5V for MAX68_ _L/M, V = +2.7V to +3.6V for MAX68_ _T/S/R ..
MAX6829SFUT+T ,Dual, Ultra-Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog TimerApplicationsMAX6828 _UT-T -40°C to +125°C 6 SOT23-6 Portable/Battery- Automotive Systems MAX6829_ _ ..
MAX3221CAE+-MAX3221CAE+T-MAX3221CAE-T-MAX3221CUE+-MAX3221CUE+T-MAX3223CAP+-MAX3223CAP+T-MAX3223CAP-T-MAX3223CPP+-MAX3223CUP+-MAX3223CUP+T-MAX3243CAI+-MAX3243CAI+T-MAX3243CAI-T-MAX3243CUI+-MAX3243CUI+T-MAX3243CUI-T
+3V to +5.5V RS-232 Transceivers with AutoShutdown
MAX3221/MAX3223/MAX3243+3V to +5.5V RS-232
Transceivers with AutoShutdown
General DescriptionThe MAX3221/MAX3223/MAX3243 achieve 1µA supply
current with Maxim’s revolutionary AutoShutdown™
feature. When the MAX3221/MAX3223/MAX3243 do not
sense a valid signal level on their receiver inputs, the
on-board power supply and drivers shut down. This
occurs if the RS-232 cable is disconnected or if the
transmitters of the connected peripheral are turned off.
The system turns on again when a valid level is applied
to any RS-232 receiver input.
The MAX3221/MAX3223/MAX3243 require only 0.1µF
capacitors in 3.3V operation, and can operate from
input voltages ranging from +3.0V to +5.5V.
A proprietary, high-efficiency, dual charge-pump power
supply and a low-dropout transmitter combine to deliv-
er true RS-232 performance from a single +3.0V to
+5.5V supply.
The MAX3221 is a 1-driver/1-receiver 16-pin SSOP
version of the 20-pin 2-driver/2-receiver MAX3223.
The MAX3243 is a 3-driver/5-receiver with a comple-
mentary always-active receiver for external monitoring
in a variety of 28 pin packages. Please see order
information table for package offerings.
ApplicationsBattery-Powered Equipment
Hand-Held Equipment
Peripherals
Portable Diagnostics Equipment
Benefits and FeaturesIntegrated Charge Pump Circuitry Simplifies Power
RequirementsEliminates the Need for a ±12 SupplyOperation From a Single +3.3V or +5V Supply
1µA Supply Current in Shutdown Mode Saves PowerAutoShutdown Feature is Enabled After No Activity
on Receiver Inputs for 30µsSoftware Control Option for Shutdown
PARTMAX3221CAE
MAX3221EUE†-40°C to +85°C
0°C to +70°C
TEMP RANGEPIN-PACKAGE16 SSOP
16 TSSOP
†Future product—contact factory for availability.
AutoShutdown and UCSP are trademarks of Maxim Integrated
Products, Inc.
Pin Configurations appear at end of data sheet.
Typical Operating Circuits appear at end of data sheet.MAX3223EPP-40°C to +85°C20 Plastic DIP
MAX3223EAP-40°C to +85°C20 SSOP
MAX3243CWI0°C to +70°C28 Wide SO
MAX3243CAI0°C to +70°C28 SSOP
MAX3243EWI-40°C to +85°C28 Wide SO
MAX3243EAI-40°C to +85°C28 SSOP
MAX3223CPP
MAX3223CAP0°C to +70°C
0°C to +70°C20 Plastic DIP
20 SSOP
Ordering Information
Selector GuideMAX3221
MAX3223
MAX3243
3.0 to 5.5
3.0 to 5.5
3.0 to 5.55
Yes
Yes
Yes
PARTTxRxVCCRANGE (V)AutoShutdownMAX3221CUE†0°C to +70°C16 TSSOP
MAX3221EAE-40°C to +85°C16 SSOP
MAX3223CUP0°C to +70°C20 TSSOP
MAX3223EUP-40°C to +85°C20 TSSOP
MAX3243CUI0°C to +70°C28 TSSOP
MAX3243EUI-40°C to +85°C28 TSSOP
MAX3221/MAX3223/MAX3243+3V to +5.5V RS-232 Transceivers
with AutoShutdown
Absolute Maximum Ratings
Electrical Characteristics(VCC= +3.0V to +5.5V, C1–C4 = 0.1µF (Note 2), 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, EN(MAX3223)......-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......................................................................Continuous
Continuous Power Dissipation (TA= +70°C)
16-Pin SSOP (derate 7.14mW/°C above +70°C)...........571mW
16-Pin TSSOP (derate 6.70mW/°C above +70°C).........533mW
20-Pin Plastic DIP (derate 11.11mW/°C above +70°C)....889mW
20-Pin SSOP (derate 8.00mW/°C above +70°C)...........640mW
20-Pin TSSOP DIP (derate 7.00mW/°C above +70°C).....559mW
28-Pin Wide SO (derate 12.50mW/°C above +70°C)............1W
28-Pin SSOP (derate 9.52mW/°C above +70°C)...........762mW
28-Pin TSSOP (derate 8.70mW/°C above +70°C).........696mW
Operating Temperature Ranges
MAX32_ _C_ _.......................................................0°C to +70°C
MAX32_ _E_ _....................................................-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 maximum magnitudes of 7V, but their absolute difference cannot exceed 13V.
IOUT= 1.6mA
Receivers disabled
T_IN, EN, FORCEON, FORCEOFF
T_IN, EN, FORCEON, FORCEOFF
T_IN, FORCEON, FORCEOFF, EN(MAX3223)
IOUT= -1.0mA
CONDITIONSVCC- 0.6VCC- 0.1Output Voltage High0.4Output Voltage Low±0.05±10Output Leakage Current±0.01±1.0Input Leakage Current2.4Input Logic Threshold High1.0100.8Input Logic Threshold Low
UNITSMINTYPMAXPARAMETERVCC= 3.3V
VCC= 5.0V
Supply Current, AutoShutdown
Supply Current, ShutdownµA1.010
Supply Current,
AutoShutdown Disabled
VCC= 3.3V
or 5.0V,= +25°C0.31.0
Receiver Positive or Negative
Threshold to INVALIDHigh (tINVH)Figure 5µs1
Receiver Threshold to
Transmitters Enabled (tWU)Figure 5µs250
Receiver Positive or NegativeFigure 5µs30
Receiver Input Thresholds to
Transmitters EnabledFigure 5V-2.7
INVALIDOutput Voltage LowIOUT= 1.6mAV0.4
Receiver Input Thresholds to
Transmitters Disabled1µA supply current, Figure 5V-0.30.3
Positive threshold
Negative threshold
INVALIDOutput Voltage HighIOUT= -1.0mAVVCC- 0.6
DC CHARACTERISTICS
LOGIC INPUTS AND RECEIVER OUTPUTS
AUTOSHUTDOWN (FORCEON = GND, FORCEOFF= VCC)
All R_IN open, FORCEON = GND,
FORCEOFF= VCC
FORCEOFF= GND
FORCEON = FORCEOFF= VCC,
no load
MAX3221/MAX3223/MAX3243+3V to +5.5V RS-232 Transceivers
with AutoShutdown
Electrical Characteristics (continued)(VCC= +3.0V to +5.5V, C1–C4 = 0.1µF (Note 2), TA= TMINto TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
Note 2:C1–C4 = 0.1µF, tested at 3.3V ±10%. C1 = 0.047µF, C2–C4 = 0.33µF, tested at 5.0V ±10%.
Normal operation200
Receiver Output Enable TimeNormal operationns
tPLH
Receiver input to receiver output, = 150pF8.030
Transition-Region Slew RateV/µs
VCC= 3.3V, = 3kΩto 7kΩ, = +25°C,
measured from +3V to
-3V or -3V to +3V
Transmitter Skew200ns⏐tPHL- tPLH⏐
PARAMETERMINTYPMAXUNITS±25
Output Short-Circuit Current±35±60mA
Output Resistance30010MΩ
Output Leakage CurrentµA
Input Threshold Low0.61.2V
±5.0±5.4Output Voltage SwingV
Maximum Data Rate120235kbps
Receiver Propagation Delay0.3µs
CONDITIONSVCC= V+ = V- = 0V, transmitter output = ±2V
VOUT= ±12V, VCC= 0V or 3.0V to 5.5V,
transmitters disabled= 3kΩ, CL= 1000pF, one transmitter switching
All transmitter outputs loaded with 3kΩto groundReceiver Output Disable Time
tPHL0.3
Input Voltage Range-2525V
Input Hysteresis0.3V
Input Threshold HighV
Input Resistance357kΩTA= +25°C
1.52.4= +25°C= +25°C
VCC= 3.3V
VCC= 3.3V
VCC= 5.0V
VCC= 5.0V= 200pF to 2500pF= 200pF to 1000pF630Transmitter Output VoltageV
T1IN = T2IN = GND, T3IN = VCC,
T3OUT loaded with 3kΩto GND, T1OUT and
T2OUT loaded with 2.5mA each
MAX3221/MAX3223
MAX32432001000
Receiver Skew100ns⏐tPHL- tPLH⏐MAX3221/MAX3223
MAX3243100500
RECEIVER INPUTS
TIMING CHARACTERISTICS
TRANSMITTER OUTPUTS
MOUSE DRIVEABILITY(MAX3243)
MAX3221/MAX3223/MAX3243+3V to +5.5V RS-232 Transceivers
with AutoShutdown
Typical Operating Characteristics(VCC= +3.3V, 235kbps data rate, 0.1µF capacitors, all transmitters loaded with 3kΩ, TA= +25°C, unless otherwise noted.)
MAX3221/MAX3223
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCEMAX3221/3223-01
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
VOUT+
VOUT-
MAX3221/MAX3223
SLEW RATE
vs. LOAD CAPACITANCE
MAX3221/3223-02
LOAD CAPACITANCE (pF)
SLEW RATE (V/
FOR DATA RATES UP TO 235kbps
+SLEW
-SLEW
MAX3221/MAX3223
SUPPLY CURRENT vs. LOAD CAPACITANCE
WHEN TRANSMITTING DATAMAX3221/3223-03
LOAD CAPACITANCE (pF)
MAX3221 SUPPLY CURRENT (mA)
235kbps
120kbps
20kbps
MAX3243
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE
MAX3221/3223-04
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
VOUT+
1 TRANSMITTER AT 235kbps
2 TRANSMITTERS AT 30kbps
VOUT-ALL OUTPUTS LOADED WITH 3kΩ +CL
0.1μF CHARGE-PUMP CAPACITORS
FOR ALL DATA RATES UP TO 235kbps4
MAX3243
SLEW RATE
vs. LOAD CAPACITANCEMAX3221/3223-05
LOAD CAPACITANCE (pF)
SLEW RATE (V/
+SLEW
-SLEW
MAX3243
SUPPLY CURRENT vs. LOAD
CAPACITANCE WHEN TRANSMITTING DATA MAX3221/3223-06
LOAD CAPACITANCE (pF)
SUPPLY CURRENT (mA)
235kbps
120kbps
20kbps
MAX3221/MAX3223/MAX3243+3V to +5.5V RS-232 Transceivers
with AutoShutdown
Pin DescriptionNoninverting Receiver Output—active in shutdownR2OUTB
Output of the valid signal detector. Indicates if a valid RS-232 level is pres-
ent on receiver inputs logic “1”.INVALID
Drive low to shut down transmitters and on-board power supply. This over-
rides all automatic circuitry and FORCEON (Table 1).FORCEOFF
Drive high to override automatic circuitry keeping transmitters on
(FORCEOFFmust be high) (Table 1).FORCEON
Negative terminal of the voltage doubler charge-pump capacitorC1-
RS-232 Receiver InputsR_IN
RS-232 Transmitter OutputsT_OUT
TTL/CMOS Transmitter InputsT_IN
TTL/CMOS Receiver OutputsR_OUT
-5.5V generated by the charge pumpV-
Negative terminal of inverting charge-pump capacitorC2-
Positive terminal of inverting charge-pump capacitorC2+
Receiver Enable Control. Drive low for normal operation. Drive high to force
the receiver outputs into a high-Z state.EN
FUNCTIONGroundGND
+3.0V to +5.5V Supply VoltageVCC
LapLink is a trademark of Traveling Software.
Detailed Description
Dual Charge-Pump Voltage ConverterThe MAX3221/MAX3223/MAX3243’s 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 flying capacitor (C1, C2) and
a reservoir capacitor (C3, C4) to generate the V+ and
V- supplies.
RS-232 TransmittersThe transmitters are inverting level translators that con-
vert CMOS-logic levels to 5.0V EIA/TIA-232 levels. They
guarantee a 120kbps data rate with worst-case loads of
3kΩin parallel with 1000pF, providing compatibility with
PC-to-PC communication software (such as Laplink™).
Typically, the MAX3221/MAX3223/MAX3243 can oper-
ate at data rates of 235kbps. Transmitters can be paral-
leled to drive multiple receivers or mice (MAX3243).
Figure 1 shows a complete system connection.
When FORCEOFFis driven to ground, or the Auto-
Shutdown circuitry senses invalid voltage levels at all
receiver inputs, the transmitters are disabled and the
outputs are forced into a high-impedance state.
NAMEMAX3221+5.5V generated by the charge pumpV+3
Positive terminal of the voltage doubler charge-pump capacitorC1+2
9, 16
8, 17
12, 13
10, 15
9, 10, 11
12, 13, 14
MAX3223
MAX324328
PIN
MAX3221/MAX3223/MAX3243+3V to +5.5V RS-232 Transceivers
with AutoShutdown
RS-232 ReceiversThe MAX3221/MAX3223/MAX3243’s receivers convert
RS-232 signals to CMOS-logic output levels. All
receivers have one inverting three-state output. In shut-
down (FORCEOFF= low) or in AutoShutdown, the
MAX3221/MAX3223’s receivers are active (Table 1).
Driving ENhigh places the receiver(s) in a high-imped-
ance state. The MAX3243’s receivers are high imped-
ance when the part is shut down.
The MAX3243 has an always-active complementary
output (R2OUTB). R2OUTB is an extra output that mon-
itors receiver activity while the other receivers are high
impedance. This allows Ring Indicator to be monitored
without forward biasing other devices connected to the
receiver outputs. This is ideal for systems where VCCis
set to 0V in shutdown to accommodate peripherals,
such as UARTs (Figure 2).
MAX3243
I/O
CHIP
WITH
UART
CPU
RS-232
POWER
MANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
FORCEOFF
FORCEON
INVALID
MAX3243
T1OUT
R2OUTB
5kΩUART
VCC
T1IN
THREE-STATED
LOGIC
TRANSITION
DETECTOR
R2IN
PROTECTION
DIODE
R2OUT
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 MAX3243: IN SHUTDOWN, R2OUTB IS USED TO MONITOR EXTERNAL DEVICES AND R2OUT IS THREE STATED, ELIMINATING A CURRENT PATH
THROUGH THE UART'S PROTECTION DIODE.
GND
PROTECTION
DIODEFigure 1. Interface Under Control of PMU
Figure 2. The MAX3243 detects RS-232 activity when the
UART and interface are shut down.
MAX3221/MAX3223/MAX3243+3V to +5.5V RS-232 Transceivers
with AutoShutdown
AutoShutdownA 1µA supply current is achieved with Maxim’s new
AutoShutdown feature, which operates when
FORCEON is low and FORCEOFFis high. When the
MAX3221/MAX3223/MAX3243 sense no valid signal
levels on all receiver inputs for 30µs, 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 the connected peripheral transmitters are
turned off. The system turns on again when a valid level
is applied to any RS-232 receiver input. As a result, the
system saves power without changes to the existing
BIOS or operating system. When using AutoShutdown,
the INVALIDoutput is high when the device is on and
low when the device is shut down. Because INVALID
indicates the receiver inputs’ condition, it can be used
in any mode (Figure 3).
Table 2 and Figure 3c summarize the MAX3221/
MAX3223/MAX3243operating modes. FORCEON and
FORCEOFFoverride the automatic circuitry and force
the transceiver into its normal operating state or into its
low-power standby state. When neither control is assert-
ed, the IC selects between these states automatically
based on receiver input levels. Figures 3a, 3b, and 5a
depict valid and invalid RS-232 receiver levels.
A mouse or other system with AutoShutdown 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 MAX3221/MAX3223/
Table 1a. MAX3221/MAX3223 FFOORRCCEEOOFFFF
and
Enable Control Truth Table
Table 1b. MAX3243 FFOORRCCEEOOFFFF
Control
Truth TableActive*11
Active*01FOORRCCEEOOFFFF
High-Z10
High-Z00
T_OUTEENN
High-Z
Active
High-Z
Active
R_OUT+0.3V
-0.3V
INVALID
TO MAX32_ _
POWER SUPPLY
AND TRANSMITTERSR_IN
* TRANSMITTERS ARE DISABLED, REDUCING SUPPLY CURRENT TO 1μA IF
ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR AT LEAST 30μs.
30µs
COUNTER
Active*1
High-Z0
T_OUTFFOORRCCEEOOFFFF
Active*
High-Z
R_OUTActive
Active
R2OUTBFigure 3a. MAX32_ _ Entering 1µA Supply Mode via
AutoShutdown
*Note:If the part is in AutoShutdown mode (FORCEOFF= VCC,
FORCEON = GND), it is shut down if no valid RS-232
levels are present on all receiver inputs.
FORCEON
MASTER SHDN LINE
0.1μF1MΩ
FORCEOFF
MAX3221
MAX3223
MAX3243
POWER
MANAGEMENT
UNIT
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a
Mouse or Another System
+2.7V
-2.7V
INVALID
TO MAX32_ _
POWER SUPPLYR_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.
30µs
COUNTER
Figure 3b. MAX32_ _ with Transmitters Enabled Using
AutoShutdown
FORCEOFFPOWER DOWN
INVALID
FORCEON
INVALID IS AN INTERNALLY GENERATED SIGNAL
THAT IS USED BY THE AUTOSHUTDOWN LOGIC
AND APPEARS AS AN OUTPUT OF THE DEVICE.
POWER DOWN IS ONLY AN INTERNAL SIGNAL.
IT CONTROLS THE OPERATIONAL STATUS OF
THE TRANSMITTERS AND THE POWER SUPPLIES.
Figure 3c. AutoShutdownLogic
MAX3221/MAX3223/MAX3243+3V to +5.5V RS-232 Transceivers
with AutoShutdown
MAX3243is awake. If the other system outputs valid
RS-232 signals within that time, the RS-232 ports on
both systems remain enabled.
When shut down, the device’s charge pumps are turned
off, V+ decays to VCC, V- decays to ground, and the
transmitter outputs are disabled (high impedance). The
time required to exit shutdown is typically 100µs (Figure
5b).
Software-Controlled ShutdownIf direct software control is desired, INVALIDcan be
used to indicate DTR or Ring Indicator signal. Tie
FORCEOFFand FORCEON together to bypass Auto-
Shutdown so the line acts like a SHDNinput.
Applications Information
Capacitor SelectionThe capacitor type used for C1–C4 is not critical for
proper operation; either polarized or nonpolarized
capacitors may be used. The charge pump requires
0.1µF capacitors for 3.3V operation. For other supply
voltages, refer to Table 3 for required capacitor values.
Do not use values smaller than those listed in Table 3.
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) usually rises at
low temperatures and influences the amount of ripple
on V+ and V-.
Table 2. AutoShutdown Logic
RS-232 SIGNAL
PRESENT AT
RECEIVER INPUTFOORRCCEEOOFFFF
INPUTFORCEON
INPUTIINNVVAALLIIDD
OUTPUTTRANSCEIVER STATUSYesHXHNormal OperationHHLNormal Operation (Forced On)HLLShutdown (AutoShutdown)
YesLXHShutdown (Forced Off)LXLShutdown (Forced Off)
VCC
VCC
tINVL
tWU
INVALID
REGION
RECEIVER
INPUT
VOLTAGE
(V)
INVALID
OUTPUT
(V)
tINVH
TRANSMITTERS ENABLED, INVALID HIGHRECEIVER INPUT LEVELS
AUTOSHUTDOWN, TRANSMITTERS DISABLED,
1μA SUPPLY CURRENT, INVALID LOW
TRANSMITTERS ENABLED, INVALID HIGH-2.7V
-0.3V
+2.7V
+0.3V
INDETERMINATE
INDETERMINATE
(b)
(a)Figure 5. AutoShutdown Trip Levels
MAX3221/MAX3223/MAX3243+3V to +5.5V RS-232 Transceivers
with AutoShutdown
Power-Supply Decoupling In most circumstances a 0.1µF bypass capacitor is
adequate. In applications that are sensitive to power-
supply noise, decouple VCCto ground with a capacitor
of the same value as the charge-pump capacitor C1.
Connect bypass capacitors as close to the IC as possible.
Transmitter Outputs
when Exiting ShutdownFigure 6 shows two transmitter outputs when exiting
shutdown mode. As they become active, the two trans-
mitter outputs are shown going to opposite RS-232
levels. Each transmitter is loaded with 3kΩin parallel
with 2500pF. The transmitter outputs display no ringing
or undesirable transients as they come out of shut-
down. Note that the transmitters are enabled only when
the magnitude of V- exceeds approximately 3V. Figure
7a shows the MAX3243’s transmitter output voltage
vs. current per transmitter. Figure 7b is a mouse driver
test circuit.
Mouse Driveability (MAX3243)The MAX3243 has been specifically designed to power
serial mice while operating from low-voltage power sup-
plies. It has been tested with samples of ten major mouse
models from six manufacturers including the leading
three: Logitech (5 models), Mouse Systems, and
Microsoft. The MAX3243 successfully drove all serial
mice and met their respective current and voltage
requirements. Figure 7a shows the transmitter outputs
under increasing load current. The MAX3243’s switching
regulator ensures the transmitters will supply at least ±5V
during worst-case conditions. The AutoShutdown feature
does not work with a mouse, so FORCEOFFand
FORCEONshould be connected to VCC.
High Data RatesThe MAX3221/MAX3223/MAX3243 maintain 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
235kbps. For Figure 9, all three transmitters were driv-
en simultaneously at 120kbps into RS-232 loads in par-
allel with 1000pF. For Figure 10, a single transmitter
was driven at 235kbps, but all three transmitters were
loaded with an RS-232 receiver in parallel with 1000pF.
Interconnection with 3V and 5V LogicThe MAX3221/MAX3223/MAX3243 can directly inter-
face with various 5V logic families, including ACT and
HCT CMOS. See Table 4 for more information on possi-
ble combinations of interconnections.234567
MAX32
LOAD CURRENT PER TRANSMITTER (mA)
TRANSMITTER OUTPUT VOLTAGE (V)
VOUT+VCC = 3.0V
VOUT-
VOUT+
VCCVOUT-
Figure 7a. MAX3243 Transmitter Output Voltage vs. Load
Current per Transmitter
5V/div
VCC = +3.3V
C1–C4 = 0.1μF
2V/div
50μs/div
Figure 6. Transmitter Outputs when Exiting Shutdown or
Powering Up
