MAX3232CSE+T ,3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External CapacitorsFeatures♦ For Smaller Packaging:The MAX3222/MAX3232/MAX3237/MAX3241 trans-MAX3228E/MAX3229E: +2.5V ..
MAX3232CSE+T ,3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitorsapplications. Both these devices feature+Denotes lead-free package.a shutdown mode in which all rec ..
MAX3232CSE+T ,3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External CapacitorsApplications C1+ V2 17 CCV+ 3 GND16Notebook, Subnotebook, and Palmtop ComputersC1- T1OUT4 15High-Sp ..
MAX3232CSE+T ,3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External CapacitorsFeatures♦ For Smaller Packaging:The MAX3222/MAX3232/MAX3237/MAX3241 trans-MAX3228E/MAX3229E: +2.5V ..
MAX3232CSE-T ,3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitorsapplications. Both these devices feature+Denotes lead-free package.a shutdown mode in which all rec ..
MAX3232CUE ,3.0V to 5.5V / Low-Power / up to 1Mbps / True RS-232 Transceivers Using Four 0.1F External Capacitorsfeatures a 1µA shutdown mode' Pin Compatible with Industry-Standard MAX232that reduces power consum ..
MAX667ESA ,+5V/Programmable Low-Dropout Voltage Regulatorapplications where the input voltages______________Ordering Informationare above +3.5V. Choose the ..
MAX667ESA ,+5V/Programmable Low-Dropout Voltage RegulatorGeneral Description ________
MAX667ESA+ ,+5V Programmable, Low-Dropout Voltage RegulatorFeaturesThe MAX667 low-dropout, positive, linear voltage regu-♦ 350mV Max Dropout at 200mAlator sup ..
MAX667ESA+T ,+5V Programmable, Low-Dropout Voltage RegulatorELECTRICAL CHARACTERISTICS(GND = 0V, V = +9V, V = +5V, C1 = 10µF, unless otherwise noted.)IN OUT T ..
MAX667MJA ,+5V/Programmable Low-Dropout Voltage RegulatorGeneral Description ________
MAX6680MEE+ ,±1°C Fail-Safe Remote/Local Temperature Sensors with SMBus InterfaceFeaturesThe MAX6680/MAX6681 are precise, two-channel digi-♦ Two Alarm Outputs: ALERT and OVERTtal t ..
MAX3222CAP+-MAX3222CAP+T-MAX3222CAP+TG068-MAX3222CUP+-MAX3222CUP+T-MAX3222CWN+-MAX3222CWN+T-MAX3222CWN-T-MAX3232CAE-MAX3232CAE+-MAX3232CAE+T-MAX3232CPE+-MAX3232CSE+-MAX3232CSE+T-MAX3232CSE-T-MAX3232CUE+-MAX3232CUE+T-MAX3232CWE+-MAX3232CWE+T-MAX3232CWE-T-MAX3232ICAE
3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitors
MAX3222/MAX3232/
MAX3237/MAX3241*
3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232ransceivers Using Four 0.1µF External CapacitorsEVALUATION KIT AVAILABLE
________________General DescriptionThe MAX3222/MAX3232/MAX3237/MAX3241 trans-
ceivers have a proprietary low-dropout transmitter out-
put stage enabling true RS-232 performance from a
3.0V to 5.5V supply with a dual charge pump. The
devices require only four small 0.1µF external charge-
pump capacitors. The MAX3222, MAX3232, and
MAX3241 are guaranteed to run at data rates of
120kbps while maintaining RS-232 output levels. The
MAX3237 is guaranteed to run at data rates of 250kbps
in the normal operating mode and 1Mbps in the
MegaBaud™ operating mode, while maintaining RS-232
output levels.
The MAX3222/MAX3232 have 2 receivers and 2
drivers. The MAX3222 features a 1µA shutdown mode
that reduces power consumption and extends battery
life in portable systems. Its receivers remain active in
shutdown mode, allowing external devices such as
modems to be monitored using only 1µA supply cur-
rent. The MAX3222 and MAX3232 are pin, package,
and functionally compatible with the industry-standard
MAX242 and MAX232, respectively.
The MAX3241 is a complete serial port (3 drivers/
5 receivers) designed for notebook and subnotebook
computers. The MAX3237 (5 drivers/3 receivers) is ideal
for fast modem applications. Both these devices feature
a shutdown mode in which all receivers can remain
active while using only 1µA supply current. Receivers R1
(MAX3237/MAX3241) and R2 (MAX3241) have extra out-
puts in addition to their standard outputs. These extra
outputs are always active, allowing external devices
such as a modem to be monitored without forward bias-
ing the protection diodes in circuitry that may have VCC
completely removed.
The MAX3222, MAX3232, and MAX3241 are available
in space-saving TSSOP and SSOP packages.
________________________ApplicationsNotebook, Subnotebook, and Palmtop Computers
High-Speed Modems
Battery-Powered Equipment
Hand-Held Equipment
Peripherals
Printers
__Next Generation Device FeaturesFor Smaller Packaging:
MAX3228E/MAX3229E: +2.5V to +5.5V RS-232
Transceivers in UCSP™For Integrated ESD Protection:
MAX3222E/MAX3232E/MAX3237E/MAX3241E*/
MAX3246E: ±15kV ESD-Protected, Down to 10nA,
3.0V to 5.5V, Up to 1Mbps, True RS-232
TransceiversFor Low-Voltage or Data Cable Applications:
MAX3380E/MAX3381E: +2.35V to +5.5V, 1µA,
2Tx/2Rx RS-232 Transceivers with ±15kV
ESD-Protected I/O and Logic PinsSHDN
VCC
GND
T1OUTC1-
C1+
TOP VIEW
R1IN
R1OUT
T1IN
T2INT2OUT
C2-
C2+9R2OUTR2IN
DIP/SOMAX3222
_________________Pin Configurations
_______________Ordering InformationMegaBaud and UCSP are trademarks of Maxim Integrated Products, Inc.
Typical Operating Circuits appear at end of data sheet.Pin Configurations continued at end of data sheet.
Ordering Information continued at end of data sheet.+Denotes lead-free package.
PARTTEMP RANGEPIN-PACKAGEPKG
CODE
MAX3222CUP+ 0°C to +70°C 20 TSSOP U20+2
MAX3222CAP+ 0°C to +70°C 20 SSOP A20+1
MAX3222CWN+ 0°C to +70°C 18 SO W18+1
MAX3222CPN+ 0°C to +70°C 18 Plastic Dip P18+5
3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232ransceivers Using Four 0.1µF External Capacitors
MAX3222/MAX3232/MAX3237/MAX3241VCC= 5.0V
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.
Note 1:V+ and V- can have a maximum magnitude of 7V, but their absolute difference cannot exceed 13V.
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, SHDN, EN...................................................-0.3V to +6V
MBAUD...................................................-0.3V to (VCC+ 0.3V)
R_IN.................................................................................±25V
Output Voltages
T_OUT...........................................................................±13.2V
R_OUT....................................................-0.3V to (VCC+ 0.3V)Short-Circuit Duration
T_OUT....................................................................Continuous
Continuous Power Dissipation (TA= +70°C)
16-Pin TSSOP (derate 6.7mW/°C above +70°C).............533mW
16-Pin Narrow SO (derate 8.70mW/°C above +70°C)....696mW
16-Pin Wide SO (derate 9.52mW/°C above +70°C)........762mW
16-Pin Plastic DIP (derate 10.53mW/°C above +70°C)...842mW
18-Pin SO (derate 9.52mW/°C above +70°C)..............762mW
18-Pin Plastic DIP (derate 11.11mW/°C above +70°C)..889mW
20-Pin SSOP (derate 7.00mW/°C above +70°C).........559mW
20-Pin TSSOP (derate 8.0mW/°C above +70°C).............640mW
28-Pin TSSOP (derate 8.7mW/°C above +70°C).............696mW
28-Pin SSOP (derate 9.52mW/°C above +70°C).........762mW
28-Pin SO (derate 12.50mW/°C above +70°C).....................1W
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
IOUT= -1.0mA
IOUT= 1.6mA
Receivers disabled
T_IN, EN, SHDN, MBAUD
T_IN, EN, SHDN, MBAUD
CONDITIONS0.81.5Input Threshold Low0.61.2-2525Input Voltage Range
VCCPower-Supply CurrentVCC- 0.6VCC- 0.1Output Voltage High0.4Output Voltage Low±0.05±10Output Leakage Current±0.01±1.0Input Leakage Current0.8Input Logic Threshold Low
(Note 3)
UNITSMINTYPMAXPARAMETER= +25°C= +25°CV1.82.4Input Threshold High1.52.4
VCC= 3.3V
VCC= 5.0V
2.0V2.4
Input Logic Threshold High
(Note 3)
No load, VCC= 3.3V or 5.0V,= +25°CmA0.31.0MAX3222/MAX3232/
MAX3241
MAX3237
SHDN= GND, TA= +25°CµA1.010Shutdown Supply Current
VCC= 3.3V
VCC= 5.0V
VCC= 3.3V
VCC= 5.0V
DC CHARACTERISTICS
LOGIC INPUTS AND RECEIVER OUTPUTS
RECEIVER INPUTS
3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232ransceivers Using Four 0.1µF External Capacitors
MAX3222/MAX3232/MAX3237/MAX3241
TIMING CHARACTERISTICS—MAX3222/MAX3232/MAX3241(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.)
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.)
T1IN = T2IN = GND, T3IN = VCC,
T3OUT loaded with 3kΩto GND,
T1OUT and T2OUT loaded with 2.5mA each
CONDITIONS±5.0Transmitter Output Voltage0.3Input Hysteresis
UNITSMINTYPMAXPARAMETERAll transmitter outputs loaded with 3kΩto groundV±5.0±5.4Output Voltage Swing±35±60Output Short-Circuit Current
VCC= V+ = V- = 0V, VOUT= ±2VΩ30010MOutput Resistance
VOUT= ±12V, VCC= 0V or 3V to 5.5V, transmitters
disabledµA±25Output Leakage Current
tPHL= 3kΩ, CL= 1000pF, one transmitter switching
tPLHtPHL- tPLH|tPHL- tPLH|
Normal operation
Normal operation
CONDITIONS0.3µs0.3Receiver Propagation Delay
kbps120235Maximum Data Rate300Receiver Skew300Transmitter Skew200Receiver Output Disable Time200Receiver Output Enable Time
UNITSMINTYPMAXPARAMETER630VCC= 3.3V, RL= 3kΩto 7kΩ,
+3V to -3V or -3V to +3V,= +25°C, one transmitter
switching
V/µs
Transition-Region Slew Rate
R_IN to R_OUT, CL= 150pF= 150pF to
1000pF= 150pF to
2500pF= +25°CkΩ357Input Resistance
MOUSE DRIVEABILITY (MAX3241)
TRANSMITTER OUTPUTS
3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232ransceivers Using Four 0.1µF External Capacitors
MAX3222/MAX3232/MAX3237/MAX3241
__________________________________________Typical Operating Characteristics(VCC= +3.3V, 235kbps data rate, 0.1µF capacitors, all transmitters loaded with 3kΩ, TA= +25°C, unless otherwise noted.)= 3kΩ, CL= 1000pF, one transmitter switching,
MBAUD = GND
Normal operation
CONDITIONSNormal operationns200Receiver Output Disable TimetPHL- tPLH|, MBAUD = GNDns100
2500.15Receiver Propagation Delay200Receiver Output Enable Time
UNITSMINTYPMAXPARAMETER
TIMING CHARACTERISTICS—MAX3237(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.)
VCC= 3.0V to 4.5V, RL= 3kΩ, CL= 250pF,
one transmitter switching, MBAUD = VCC1000
VCC= 4.5V to 5.5V, RL= 3kΩ, CL= 1000pF,
one transmitter switching, MBAUD = VCC
kbps
Maximum Data Rate
R_IN to R_OUT, CL= 150pFtPHL- tPLH|, MBAUD = VCCns25Transmitter SkewtPHL- tPLH|ns50Receiver Skew
V/µs
tPHL
tPLH= 150pF to 2500pF,
MBAUD = GND= 150pF
to 1000pF
MBAUD =
GND
VCC= 3.3V, RL= 3Ωto 7kΩ,
+3V to -3V or -3V to +3V,= +25°C
Transition-Region Slew RateMBAUD =
VCC24150
Note 2:MAX3222/MAX3232/MAX3241: C1–C4 = 0.1µF tested at 3.3V ±10%; C1 = 0.047µF, C2–C4 = 0.33µF tested at 5.0V ±10%.
MAX3237: C1–C4 = 0.1µF tested at 3.3V ±5%; C1–C4 = 0.22µF tested at 3.3V ±10%; C1 = 0.047µF, C2–C4 = 0.33µF tested
at 5.0V ±10%.
Note 3:Transmitter input hysteresis is typically 250mV.
MAX3222/MAX3232
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCEMAX3222-01
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
VOUT+
VOUT-
MAX3222/MAX3232
SLEW RATE
vs. LOAD CAPACITANCE
MAX3222-02
LOAD CAPACITANCE (pF)
SLEW RATE (V/
FOR DATA RATES UP TO 235kbps
+SLEW
-SLEW
MAX3222/MAX3232
SUPPLY CURRENT vs. LOAD CAPACITANCE
WHEN TRANSMITTING DATAMAX3222-03
LOAD CAPACITANCE (pF)
SUPPLY CURRENT (mA)
235kbps
120kbps
20kbps
3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232ransceivers Using Four 0.1µF External Capacitors
MAX3222/MAX3232/MAX3237/MAX3241MAX3241
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE
MAX3222-04
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
MAX3241
SLEW RATE
vs. LOAD CAPACITANCEMAX3222-05
LOAD CAPACITANCE (pF)
SLEW RATE (V/
+SLEW
-SLEW
MAX3241
SUPPLY CURRENT vs. LOAD
CAPACITANCE WHEN TRANSMITTING DATA MAX3222-06
LOAD CAPACITANCE (pF)
SUPPLY CURRENT (mA)
235kbps
120kbps
20kbps
MAX3237
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE (MBAUD = GND)
MAX3222-07
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
1 TRANSMITTER AT 240kbps
4 TRANSMITTERS AT 15kbps
3kΩ + CL LOADS
VCC = 3.3V
MAX3237
SLEW RATE vs. LOAD CAPACITANCE
(MBAUD = VCC)MAX3222-10
LOAD CAPACITANCE (pF)
SLEW RATE (V/
-SLEW, 1Mbps
+SLEW, 1Mbps
1 TRANSMITTER AT FULL DATA RATE
4 TRANSMITTERS AT 1/16 DATA RATE
3kΩ + CL LOAD EACH OUTPUT
VCC = 3.3V
-SLEW, 2Mbps
+SLEW, 2Mbps
MAX3237
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE (MBAUD = VCC)
MAX3222-08
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
1 TRANSMITTER AT FULL DATA RATE
4 TRANSMITTERS AT 1/16 DATA RATE
3kΩ + CL LOAD, EACH OUTPUT
VCC = 3.3V
2Mbps1.5Mbps
1Mbps
2Mbps
1Mbps
1.5Mbps
MAX3237
SUPPLY CURRENT vs.
LOAD CAPACITANCE (MBAUD = GND)MAX3222-11
LOAD CAPACITANCE (pF)
SUPPLY CURRENT (mA)
240kbps
120kbps
20kbps
1 TRANSMITTER AT FULL DATA RATE
4 TRANSMITTERS AT 1/16 DATA RATE
3kΩ + CL LOADS
VCC = 3.3V
MAX3237
SLEW RATE vs. LOAD CAPACITANCE
(MBAUD = GND)MAX3222-09
LOAD CAPACITANCE (pF)
SLEW RATE (V/
+SLEW
-SLEW
1 TRANSMITTER AT 240kbps
4 TRANSMITTERS AT 15kbps
3kΩ + CL LOADS
VCC = 3.3V
MAX3237
SKEW vs. LOAD CAPACITANCE
(tPLH - tPHL)MAX3222-12
LOAD CAPACITANCE (pF)
MAX
MIN
AVERAGE; 10 PARTS
SKEW (ns)
1 TRANSMITTER AT 512kbps
4 TRANSMITTERS AT 32kbps
3kΩ + CL LOADS
VCC = 3.3V
MBAUD = VCC
_____________________________Typical Operating Characteristics (continued)(VCC= +3.3V, 235kbps data rate, 0.1µF capacitors, all transmitters loaded with 3kΩ, TA= +25°C, unless otherwise noted.)
3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232ransceivers Using Four 0.1µF External Capacitors
MAX3222/MAX3232/MAX3237/MAX3241
FUNCTION
MAX3222Noninverting Complementary Receiver Outputs.
Always active.
DIP/SOSSOP11, 141Receiver Enable. Active low.2Positive Terminal of Voltage-Doubler Charge-Pump
Capacitor6Negative Terminal of Inverting Charge-Pump
Capacitor5Positive Terminal of Inverting Charge-Pump
Capacitor4Negative Terminal of Voltage-Doubler Charge-Pump
Capacitor3+5.5V Generated by the Charge Pump
11, 1212, 13TTL/CMOS Transmitter Inputs
10, 1310, 15TTL/CMOS Receiver Outputs
9, 149, 16RS-232 Receiver Inputs
8, 158, 17RS-232 Transmitter Outputs7-5.5V Generated by the Charge Pump20Shutdown Control. Active low.19+3.0V to +5.5V Supply Voltage18Ground
No Connection
MAX3237MAX3232161328312527
10, 1117, 19, 22,
23, 24
9, 1218, 20, 21
8, 138, 9, 11
7, 145, 6, 7,
10, 12414262—
NAMEC1+
C2-
C2+
C1-
T_IN
R_OUT
R_IN
T_OUT
SHDN
VCC
GND
R_OUTB
N.C.
MAX324120, 21
12, 13, 14
9, 10, 11
PIN—MegaBaud Control Input. Connect to GND for normal
operation; connect to VCCfor 1Mbps transmission rates.—15MBAUD—
______________________________________________________________Pin Description
3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232ransceivers Using Four 0.1µF External Capacitors
MAX3222/MAX3232/MAX3237/MAX3241
_______________Detailed Description
Dual Charge-Pump Voltage ConverterThe MAX3222/MAX3232/MAX3237/MAX3241’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, and 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.
The MAX3222/MAX3232/MAX3241 transmitters guaran-
tee 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, these three devices can operate at data rates
of 235kbps. Transmitters can be paralleled to drive multi-
ple receivers or mice.
The MAX3222/MAX3237/MAX3241’s output stage is
turned off (high impedance) when the device is in shut-
down mode. When the power is off, the MAX3222/
MAX3232/MAX3237/MAX3241 permit the outputs to be
driven up to ±12V.
The transmitter inputs do not have pullup resistors.
Connect unused inputs to GND or VCC.
MAX3237 MegaBaud OperationIn normal operating mode (MBAUD = GND), the
MAX3237 transmitters guarantee a 250kbps data rate
with worst-case loads of 3kΩin parallel with 1000pF.
This provides compatibility with PC-to-PC communica-
tion software, such as LapLink.
For higher speed serial communications, the MAX3237
features MegaBaud operation. In MegaBaud operating
mode (MBAUD = VCC), the MAX3237 transmitters guar-
antee a 1Mbps data rate with worst-case loads of 3kΩin
parallel with 250pF for 3.0V < VCC < 4.5V. For 5V ±10%
operation, the MAX3237 transmitters guarantee a 1Mbps
data rate into worst-case loads of 3kΩin parallel with
1000pF.
MAX3222
MAX3232
MAX3237
MAX3241
5kΩ
R_ INR_ OUT
EN*
C2-
C2+
C1-
C1+VCCC1
C2
0.1µF
VCC
SHDN*
T_ OUTT_ IN
GND
VCC
7kΩ150pF
MAX3222
MAX3232
MAX3237
MAX3241
5kΩ
R_ INR_ OUT
EN*
C2-
C2+
C1-
C1+VCCC1
C2
0.1µF
VCC
SHDN*
T_ OUTT_ IN
GND
VCC
3kΩ2500pF
MINIMUM SLEW-RATE TEST CIRCUITMAXIMUM SLEW-RATE TEST CIRCUIT*MAX3222/MAX3237/MAX3241 ONLY
Figure 1. Slew-Rate Test Circuits
LapLink is a trademark of Traveling Software, Inc.
3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232ransceivers Using Four 0.1µF External Capacitors
MAX3222/MAX3232/MAX3237/MAX3241
RS-232 ReceiversThe receivers convert RS-232 signals to CMOS-logic out-
put levels. The MAX3222/MAX3237/MAX3241 receivers
have inverting three-state outputs. In shutdown, the
receivers can be active or inactive (Table 1).
The complementary outputs on the MAX3237 (R1OUTB)
and the MAX3241 (R1OUTB, R2OUTB) are always active,
regardless of the state of ENor SHDN. This allows for
Ring Indicator applications 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).
MAX3222/MAX3237/MAX3241
Shutdown ModeSupply current falls to less than 1µA in shutdown mode
(SHDN= low). When shut down, the device’s charge
pumps are turned off, V+ is pulled down to VCC, V- is
pulled to ground, and the transmitter outputs are dis-
abled (high impedance). The time required to exit shut-
down is typically 100µs, as shown in Figure 3. Connect
SHDN to VCCif the shutdown mode is not used. SHDN
has no effect on R_OUT or R_OUTB.
MAX3222/MAX3237/MAX3241
Enable ControlThe inverting receiver outputs (R_OUT) are put into a
high-impedance state when ENis high. The complemen-
tary outputs R1OUTB and R2OUTB are always active,
regardless of the state of ENand SHDN(Table 1). EN
has no effect on T_OUT.
__________Applications Information
Capacitor SelectionThe 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, refer to
Table 2 for required capacitor values. Do not use values
lower than those listed in Table 2. Increasing the capaci-
tor values (e.g., by a factor of 2) reduces ripple on the
transmitter outputs and slightly reduces power consump-
tion. 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 exces-
sively with temperature. If in doubt, use capacitors with a
higher nominal value. The capacitor’s equivalent series
resistance (ESR), which usually rises at low tempera-
tures, influences the amount of ripple on V+ and V-.
MAX3237
MAX3241
T1OUT
R1OUTB
UART
VCC
T1IN
LOGIC
TRANSITION
DETECTOR
R1INR1OUT
EN = VCC
SHDN = GND
VCC
PREVIOUS
RS-232
UART
PROTECTION
DIODE
PROTECTION
DIODE
SHDN = GND
VCC
VCC
GND
5kΩ
a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE RECEIVER OUTPUT IN SHUTDOWN.
b) NEW MAX3237/MAX3241: EN SHUTS DOWN RECEIVER OUTPUTS (EXCEPT FOR B OUTPUTS), SO NO CURRENT FLOWS TO UART IN SHUTDOWN. B OUTPUTS
INDICATE RECEIVER ACTIVITY DURING SHUTDOWN WITH EN HIGH.
GND
5kΩ
Figure 2. Detection of RS-232 Activity when the UART and
Interface are Shut Down; Comparison of MAX3237/MAX3241
(b) with Previous Transceivers (a).
3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232ransceivers Using Four 0.1µF External Capacitors
MAX3222/MAX3232/MAX3237/MAX3241
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 charge-pump capacitor C1. Connect
bypass capacitors as close to the IC as possible.
Operation Down to 2.7VTransmitter outputs will meet EIA/TIA-562 levels of
±3.7V with supply voltages as low as 2.7V.
Transmitter Outputs when
Exiting ShutdownFigure 3 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
undesirable transients as they come out of shutdown.
Note that the transmitters are enabled only when the
magnitude of V- exceeds approximately 3V.
Mouse DriveabilityThe MAX3241 has been specifically designed to power
serial mice while operating from low-voltage power sup-
plies. It has been tested with leading mouse brands from
manufacturers such as Microsoft and Logitech. The
MAX3241 successfully drove all serial mice tested and
met their respective current and voltage requirements.
Figure 4a shows the transmitter output voltages under
increasing load current at 3.0V. Figure 4b shows a typical
mouse connection using the MAX3241.
Table 1. MAX3222/MAX3237/MAX3241
Shutdown and Enable Control Truth Table
Table 2. Required Minimum Capacitor Values5V/div
VCC = 3.3V
C1–C4 = 0.1µF
2V/div
50µs/div
Figure 3. Transmitter Outputs when Exiting Shutdown or
Powering Up
VCC
(V)
(µF)4.5 to 5.50.047
3.0 to 5.50.1
C2, C3, C4
(µF)
MAX3222/MAX3232/MAX32410.47Active
Active1SHHDDNN
High-Z10
High-Z00
T_OUTEENN
High-Z
Active
High-Z
Active
R_OUT
R_OUTB
(MAX3237/
MAX3241)Active
Active
Active
Active
3.0 to 3.60.22
3.15 to 3.60.1
MAX32374.5 to 5.50.047
3.0 to 5.50.22
3.0 to 3.60.10.1
