MAX3232ESE+T

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MAX3222/MAX3232/ MAX3237/MAX3241* 3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitors EVALUATION KIT AVAILABLE For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com. 19-0273; Rev 7; 1/07 ________________General Description The 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. ________________________Applications Notebook, Subnotebook, and Palmtop Computers High-Speed Modems Battery-Powered Equipment Hand-Held Equipment Peripherals Printers __Next Generation Device Features  For 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 Transceivers  For 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 Pins 18 17 16 15 14 13 12 11 1 2 3 4 5 6 7 8 SHDN VCC GND T1OUTC1- V+ C1+ EN TOP VIEW R1IN R1OUT T1IN T2INT2OUT V- C2- C2+ 109 R2OUTR2IN DIP/SO MAX3222 + _________________Pin Configurations _______________Ordering Information MegaBaud and UCSP are trademarks of Maxim Integrated Products, Inc. *Covered by U.S. Patent numbers 4,636,930; 4,679,134; 4,777,577; 4,797,899; 4,809,152; 4,897,774; 4,999,761; and other patents pending. 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. PART TEMP RANGE PIN-PACKAGE PKG 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

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3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitors 2 Maxim Integrated MAX3222/MAX3232/MAX3237/MAX3241 VCC = 5.0V ABSOLUTE MAXIMUM RATINGS ELECTRICAL CHARACTERISTICS (VCC = +3.0V to +5.5V, C1–C4 = 0.1µF (Note 2), TA = TMIN to 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 CONDITIONS V 0.8 1.5 Input Threshold Low 0.6 1.2 V-25 25Input Voltage Range 0.5 2.0 VCC Power-Supply Current VVCC - 0.6 VCC - 0.1Output Voltage High V0.4Output Voltage Low µA±0.05 ±10Output Leakage Current µA±0.01 ±1.0Input Leakage Current V0.8 Input Logic Threshold Low (Note 3) UNITSMIN TYP MAXPARAMETER TA = +25°C TA = +25°C V 1.8 2.4 Input Threshold High 1.5 2.4 VCC = 3.3V VCC = 5.0V 2.0 V 2.4 Input Logic Threshold High (Note 3) No load, VCC = 3.3V or 5.0V, TA = +25°C mA 0.3 1.0 MAX3222/MAX3232/ MAX3241 MAX3237 SHDN = GND, TA = +25°C µA1.0 10Shutdown Supply Current VCC = 3.3V VCC = 5.0V VCC = 3.3V VCC = 5.0V DC CHARACTERISTICS LOGIC INPUTS AND RECEIVER OUTPUTS RECEIVER INPUTS

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3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitors Maxim Integrated 3 MAX3222/MAX3232/MAX3237/MAX3241 TIMING CHARACTERISTICS—MAX3222/MAX3232/MAX3241 (VCC = +3.0V to +5.5V, C1–C4 = 0.1µF (Note 2), TA = TMIN to 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 = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) T1IN = T2IN = GND, T3IN = VCC, T3OUT loaded with 3kΩ to GND, T1OUT and T2OUT loaded with 2.5mA each CONDITIONS V±5.0Transmitter Output Voltage V0.3Input Hysteresis UNITSMIN TYP MAXPARAMETER All transmitter outputs loaded with 3kΩ to ground V±5.0 ±5.4Output Voltage Swing mA±35 ±60Output Short-Circuit Current VCC = V+ = V- = 0V, VOUT = ±2V Ω300 10MOutput Resistance VOUT = ±12V, VCC = 0V or 3V to 5.5V, transmitters disabled µA±25Output Leakage Current tPHL RL = 3kΩ, CL = 1000pF, one transmitter switching tPLH | tPHL - tPLH | | tPHL - tPLH | Normal operation Normal operation CONDITIONS 0.3 µs 0.3 Receiver Propagation Delay kbps120 235Maximum Data Rate ns300Receiver Skew ns300Transmitter Skew ns200Receiver Output Disable Time ns200Receiver Output Enable Time UNITSMIN TYP MAXPARAMETER 6 30VCC = 3.3V, RL = 3kΩ to 7kΩ, +3V to -3V or -3V to +3V, TA = +25°C, one transmitter switching V/µs 4 30 Transition-Region Slew Rate R_IN to R_OUT, CL = 150pF CL = 150pF to 1000pF CL = 150pF to 2500pF TA = +25°C kΩ3 5 7Input Resistance MOUSE DRIVEABILITY (MAX3241) TRANSMITTER OUTPUTS

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3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitors 4 Maxim Integrated 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.) RL = 3kΩ, CL = 1000pF, one transmitter switching, MBAUD = GND Normal operation CONDITIONS Normal operation ns200Receiver Output Disable Time | tPHL - tPLH |, MBAUD = GND ns100 0.15 250 µs 0.15 Receiver Propagation Delay ns200Receiver Output Enable Time UNITSMIN TYP MAXPARAMETER TIMING CHARACTERISTICS—MAX3237 (VCC = +3.0V to +5.5V, C1–C4 = 0.1µF (Note 2), TA = TMIN to 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 = VCC 1000 VCC = 4.5V to 5.5V, RL = 3kΩ, CL = 1000pF, one transmitter switching, MBAUD = VCC kbps 1000 Maximum Data Rate R_IN to R_OUT, CL = 150pF | tPHL - tPLH |, MBAUD = VCC ns25 Transmitter Skew | tPHL - tPLH | ns50Receiver Skew 6 30 V/µs 4 30 tPHL tPLH CL = 150pF to 2500pF, MBAUD = GND CL = 150pF to 1000pF MBAUD = GND VCC = 3.3V, RL = 3Ω to 7kΩ, +3V to -3V or -3V to +3V, TA = +25°C Transition-Region Slew Rate MBAUD = VCC 24 150 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. -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 0 MAX3222/MAX3232 TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE M A X 32 22 -0 1 LOAD CAPACITANCE (pF) TR A N S M IT TE R O U TP U T V O LT A G E (V ) 2000 30001000 4000 5000 VOUT+ VOUT- 0 2 4 6 8 10 12 14 16 18 20 22 150 MAX3222/MAX3232 SLEW RATE vs. LOAD CAPACITANCE M A X 32 22 -0 2 LOAD CAPACITANCE (pF) S LE W R A TE ( V /μ s) 2000 30001000 4000 5000 FOR DATA RATES UP TO 235kbps +SLEW -SLEW 0 5 10 15 20 25 30 35 40 0 MAX3222/MAX3232 SUPPLY CURRENT vs. LOAD CAPACITANCE WHEN TRANSMITTING DATA M A X 32 22 -0 3 LOAD CAPACITANCE (pF) S U P P LY C U R R EN T (m A ) 2000 30001000 4000 5000 235kbps 120kbps 20kbps

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3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitors Maxim Integrated 5 MAX3222/MAX3232/MAX3237/MAX3241 -7.5 -5.0 -2.5 0 2.5 5.0 7.5 0 MAX3241 TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE M A X 32 22 -0 4 LOAD CAPACITANCE (pF) TR A N S M IT TE R O U TP U T V O LT A G E (V ) 2000 30001000 4000 5000 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 235kbps 4 6 8 10 12 14 16 18 20 22 24 0 MAX3241 SLEW RATE vs. LOAD CAPACITANCE M A X 32 22 -0 5 LOAD CAPACITANCE (pF) S LE W R A TE ( V /μ s) 2000 30001000 4000 5000 +SLEW -SLEW 0 5 10 15 20 25 30 35 45 40 0 MAX3241 SUPPLY CURRENT vs. LOAD CAPACITANCE WHEN TRANSMITTING DATA M A X 32 22 -0 6 LOAD CAPACITANCE (pF) S U P P LY C U R R EN T (m A ) 2000 30001000 4000 5000 235kbps 120kbps 20kbps -7.5 -5.0 -2.5 0 2.5 5.0 7.5 0 MAX3237 TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE (MBAUD = GND) M A X 32 22 -0 7 LOAD CAPACITANCE (pF) TR A N S M IT TE R O U TP U T V O LT A G E (V ) 2000 30001000 4000 5000 1 TRANSMITTER AT 240kbps 4 TRANSMITTERS AT 15kbps 3kΩ + CL LOADS VCC = 3.3V 0 10 20 30 50 40 60 70 0 MAX3237 SLEW RATE vs. LOAD CAPACITANCE (MBAUD = VCC) M A X 32 22 -1 0 LOAD CAPACITANCE (pF) S LE W R A TE ( V /μ s) 500 1000 1500 2000 -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 -7.5 -5.0 -2.5 0 2.5 5.0 7.5 0 MAX3237 TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE (MBAUD = VCC) M A X 32 22 -0 8 LOAD CAPACITANCE (pF) TR A N S M IT TE R O U TP U T V O LT A G E (V ) 500 1000 1500 2000 1 TRANSMITTER AT FULL DATA RATE 4 TRANSMITTERS AT 1/16 DATA RATE 3kΩ + CL LOAD, EACH OUTPUT VCC = 3.3V 2Mbps 1.5Mbps 1Mbps 2Mbps 1Mbps 1.5Mbps 0 10 20 30 40 50 60 0 MAX3237 SUPPLY CURRENT vs. LOAD CAPACITANCE (MBAUD = GND) M A X 32 22 -1 1 LOAD CAPACITANCE (pF) S U P P LY C U R R EN T (m A ) 2000 30001000 4000 5000 240kbps 120kbps 20kbps 1 TRANSMITTER AT FULL DATA RATE 4 TRANSMITTERS AT 1/16 DATA RATE 3kΩ + CL LOADS VCC = 3.3V 0 2 4 6 8 10 12 0 MAX3237 SLEW RATE vs. LOAD CAPACITANCE (MBAUD = GND) M A X 32 22 -0 9 LOAD CAPACITANCE (pF) S LE W R A TE ( V /μ s) 2000 30001000 4000 5000 +SLEW -SLEW 1 TRANSMITTER AT 240kbps 4 TRANSMITTERS AT 15kbps 3kΩ + CL LOADS VCC = 3.3V 0 10 30 20 40 50 60 70 0 MAX3237 SKEW vs. LOAD CAPACITANCE (tPLH - tPHL) M A X 32 22 -1 2 LOAD CAPACITANCE (pF) 1000 1500500 2000 2500 MAX MIN AVERAGE; 10 PARTS S K EW ( 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.)

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3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitors 6 Maxim Integrated MAX3222/MAX3232/MAX3237/MAX3241 — FUNCTION — MAX3222 Noninverting Complementary Receiver Outputs. Always active. DIP/SO SSOP — 11, 14 1 1 Receiver Enable. Active low. 2 2 Positive Terminal of Voltage-Doubler Charge-Pump Capacitor 6 6 Negative Terminal of Inverting Charge-Pump Capacitor 5 5 Positive Terminal of Inverting Charge-Pump Capacitor 4 4 Negative Terminal of Voltage-Doubler Charge-Pump Capacitor 3 3 +5.5V Generated by the Charge Pump 11, 12 12, 13 TTL/CMOS Transmitter Inputs 10, 13 10, 15 TTL/CMOS Receiver Outputs 9, 14 9, 16 RS-232 Receiver Inputs 8, 15 8, 17 RS-232 Transmitter Outputs 7 7 -5.5V Generated by the Charge Pump 18 20 Shutdown Control. Active low. 17 19 +3.0V to +5.5V Supply Voltage 16 18 Ground No Connection MAX3237MAX3232 — 16 — 13 1 28 5 3 4 1 3 25 2 27 10, 11 17, 19, 22, 23, 24 9, 12 18, 20, 21 8, 13 8, 9, 11 7, 14 5, 6, 7, 10, 12 6 4 — 14 16 26 15 2 — — NAME EN C1+ C2- C2+ C1- V+ T_IN R_OUT R_IN T_OUT V- SHDN VCC GND R_OUTB N.C. MAX3241 20, 21 23 28 2 1 24 27 12, 13, 14 15–19 4–8 9, 10, 11 3 22 26 25 — PIN — — MegaBaud Control Input. Connect to GND for normal operation; connect to VCC for 1Mbps transmission rates. — 15 MBAUD— ______________________________________________________________Pin Description

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3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitors Maxim Integrated 7 MAX3222/MAX3232/MAX3237/MAX3241 _______________Detailed Description Dual Charge-Pump Voltage Converter The 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 Transmitters The 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 3kΩ in 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 Operation In normal operating mode (MBAUD = GND), the MAX3237 transmitters guarantee a 250kbps data rate with worst-case loads of 3kΩ in 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 3kΩ in 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 3kΩ in parallel with 1000pF. MAX3222 MAX3232 MAX3237 MAX3241 5kΩ R_ INR_ OUT EN* C2- C2+ C1- C1+ V- V+ VCC C4 C3C1 C2 0.1μF VCC SHDN* T_ OUTT_ IN GND VCC 0V 7kΩ 150pF MAX3222 MAX3232 MAX3237 MAX3241 5kΩ R_ INR_ OUT EN* C2- C2+ C1- C1+ V- V+ VCC C4 C3C1 C2 0.1μF VCC SHDN* T_ OUTT_ IN GND VCC 0V 3kΩ 2500pF MINIMUM SLEW-RATE TEST CIRCUIT MAXIMUM SLEW-RATE TEST CIRCUIT *MAX3222/MAX3237/MAX3241 ONLY Figure 1. Slew-Rate Test Circuits LapLink is a trademark of Traveling Software, Inc.

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3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitors 8 Maxim Integrated MAX3222/MAX3232/MAX3237/MAX3241 RS-232 Receivers The 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 EN or SHDN. This allows for Ring Indicator applications without forward biasing other devices connected to the receiver outputs. This is ideal for systems where VCC is set to 0V in shutdown to accommodate peripherals, such as UARTs (Figure 2). MAX3222/MAX3237/MAX3241 Shutdown Mode Supply 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 VCC if the shutdown mode is not used. SHDN has no effect on R_OUT or R_OUTB. MAX3222/MAX3237/MAX3241 Enable Control The inverting receiver outputs (R_OUT) are put into a high-impedance state when EN is high. The complemen- tary outputs R1OUTB and R2OUTB are always active, regardless of the state of EN and SHDN (Table 1). EN has no effect on T_OUT. __________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, 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 Tx UART VCC T1IN LOGIC TRANSITION DETECTOR R1INR1OUT EN = VCC SHDN = GND VCC TO μP Rx PREVIOUS RS-232 Tx UART PROTECTION DIODE PROTECTION DIODE SHDN = GND VCC VCC GND Rx 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).

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3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232 Transceivers Using Four 0.1µF External Capacitors Maxim Integrated 9 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 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 EIA/TIA-562 levels of ±3.7V with supply voltages as low as 2.7V. Transmitter Outputs when Exiting Shutdown Figure 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 3kΩ in 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 Driveability The 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 Values 5V/div VCC = 3.3V C1–C4 = 0.1μF 2V/div T2 50μs/div T1 Figure 3. Transmitter Outputs when Exiting Shutdown or Powering Up VCC (V) C1 (µF) 4.5 to 5.5 0.047 3.0 to 5.5 0.1 C2, C3, C4 (µF) MAX3222/MAX3232/MAX3241 0.33 0.47 1 Active 0 1 Active1 SHDN High-Z10 High-Z00 T_OUTEN High-Z Active High-Z Active R_OUT R_OUTB (MAX3237/ MAX3241) Active Active Active Active 3.0 to 3.6 0.22 3.15 to 3.6 0.1 MAX3237 0.22 0.1 4.5 to 5.5 0.047 3.0 to 5.5 0.22 0.33 1.0 3.0 to 3.6 0.1 0.1