19-1520; Rev 0; 8/99 +5V, 1µA, Single RS-232 Transceiver with AutoShutdown General Description Features M The MAX221 is a +5V-powered, single transmit/receive 'Single RS-232 Transceiver in a Small 16-Pin A RS-232 and V.28 communications interface with auto- TSSOP Package X matic shutdown/wake-up features and high data rate capabilities. '1µA Supply Current 2 The MAX221 achieves a low 1µA supply current with 'AutoShutdown Saves Power Without 2 Maxim’s revolutionary AutoShutdown™ feature. Changes to BIOS 1 AutoShutdown saves power without changes to the 'Guaranteed 250kbps Data Rate existing BIOS or operating system by entering low- power shutdown mode when the RS-232 cable is dis- connected, or when the transmitter of the connected peripheral is off. The MAX221 wakes up and drives the INVALID pin high when an active RS-232 cable is con- nected, signaling the host that a peripheral is connect- ed to the communications port. Ordering Information The MAX221 is available in a 16-pin SSOP package as PART TEMP. RANGE PIN-PACKAGE well as a 16-pin TSSOP that uses 50% less board space MAX221CUE 0°C to +70°C 16 TSSOP than a 16-pin SO. For an equivalent RS-232 transceiver with enhanced ±15kV ESD protection, refer to the MAX221CAE 0°C to +70°C 16 SSOP MAX221E data sheet. MAX221EUE -40°C to +85°C 16 TSSOP MAX221EAE -40°C to +85°C 16 SSOP Applications Maintenance/Diagnostic Ports Industrial Systems Telecommunications Typical Operating Circuit Set-Top Boxes +5V Pin Configuration CBYPASS 0.1m 2F C1+ VC 1C5 3 C0.31m F V+ C1 0.1m F 4 C1- TOP VIEW MAX221 5 7 EN 1 16 FORCEOFF C2+ V- C4 C1+ 2 15 VCC 0.1 mC2F 6 C2- 0.1m F V+ 3 14 GND 11 TIN TOUT 13 C1- 4 MAX221 13 TOUT 9 ROUT RIN 8 C2+ 5 12 FORCEON C2- 6 11 TIN 5k V- 7 10 INVALID RIN 8 9 ROUT 1 10 TO POWER- EN INVALID MANAGEMENT UNIT TSSOP/SSOP 12 16 FORCEON FORCEOFF VCC GND 14 CAPACITORS MAY BE POLARIZED OR UNPOLARIZED. AutoShutdown is a trademark of Maxim Integrated Products. ________________________________________________________________Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769.

+5V, 1µA, Single RS-232 Transceiver with AutoShutdown 1 ABSOLUTE MAXIMUM RATINGS 2 VCC ..........................................................................-0.3V to +6V Short-Circuit Duration, TOUT.....................................Continuous 2 V+ ...............................................................(VCC- 0.3V) to +14V Continuous Power Dissipation (TA= +70°C) X V- ...........................................................................-14V to +0.3V TSSOP (derated 6.7mW/°C above +70°C)................533mW Input Voltages SSOP (derated 7.1mW/°C above +70°C)..................571mW A TIN..........................................................-0.3V to (V+ + 0.3V) Operating Temperature Range M RIN.................................................................................±30V MAX221C_ _.....................................................0°C to +70°C FORCEON, FORCEOFF, EN.................-0.3V to (VCC+ 0.3V) MAX221E_ _..................................................-40°C to +85°C Output Voltages Maximum Junction Temperature ...................................+150°C TOUT..............................................(V- - 0.3V) to (V+ + 0.3V) Storage Temperature Range ...........................-65°C to +150°C ROUT, INVALID....................................-0.3V to (VCC+ 0.3V) Lead Temperature (soldering, 10sec)............................+300°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. ELECTRICAL CHARACTERISTICS (VCC = +5V ±10%, C1–C4 = 0.1µF, TA= TMINto TMAX, unless otherwise noted. Typical values are at TA= +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC CHARACTERISTICS VCCSupply Current ICC No load, TA= +25°C 5 10 mA Shutdown Supply Current ISHDN TA= +25°C, Figure 1 1 10 µA AutoShutdown Supply Current IAS 1 10 µA LOGIC INPUTS Input Leakage Current IIN TIN = 0 to VCC ±1 µA Input Threshold Low VIL TIN; EN, FORCEOFF,FORCEON 0.8 V Input Threshold High VIH TIN, EN, FORCEOFF 2.4 V Output Voltage Low VOL ROUT; ISINK= 3.2mA 0.4 V Output Voltage High VOH ROUT; ISOURCE= 1.0mA 3.5 V Output Leakage Current EN= VCC, 0 ≤ROUT ≤VCC ±0.05 ±10 µA AUTOSHUTDOWN Receiver Input Threshold, Positive threshold 2.7 Figure 3 V Transmitter Enabled Negative threshold -2.7 Receiver Input Threshold, Transmitter Disabled ICC= 1µA, Figure 3 -0.3 0.3 V INVALIDOutput Voltage Low ISINK= 1.6mA 0.4 V INVALIDOutput Voltage High ISOURCE= 1.0mA VCC- 0.6 V Receiver Threshold to Transmitter Enabled tWU Figure 3 250 µs Receiver Positive or Negative tINVH Figure 3 1 µs Threshold to INVALIDHigh Receiver Positive or Negative tINVL Figure 3 30 µs Threshold to INVALIDLow 2 _______________________________________________________________________________________

+5V, 1µA, Single RS-232 Transceiver with AutoShutdown ELECTRICAL CHARACTERISTICS (continued) M (VCC = +5V ±10%, C1–C4 = 0.1µF, TA= TMINto TMAX, unless otherwise noted. Typical values are at TA= +25°C.) A PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS X RECEIVER INPUT 2 Input Voltage Range -25 25 V 2 Input Threshold Low TA= +25°C, VCC= 5V 0.8 1.2 V 1 Input Threshold High TA= +25°C, VCC= 5V 1.7 2.4 V Input Hysteresis VCC= 5V, no hysteresis in shutdown 0.5 V Input Resistance TA= +25°C, VCC = 5V 3 5 7 kΩ TRANSMITTER OUTPUT Output Voltage Swing Driver loaded with 3kΩto ground ±5 ±9 V Output Resistance VCC = V+ = V- = 0, VOUT= ±2V 300 Ω Output Short-Circuit Current ±10 ±60 mA TIMING CHARACTERISTICS (VCC= +5V ±10%, C1–C4 = 0.1µF, TA = TMINto TMAX, unless otherwise noted. Typical values are at TA= +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Maximum Data Rate RL= 3kΩto 7kΩ, CL= 50pF to 1000pF, 250 kbps VCC= 4.5V Receiver Propagation Delay tPHL,tPLH CL= 150pF 0.15 µs Receiver Output Enable Time Normal operation 300 ns Receiver Output Disable Time Normal operation 200 ns Transmitter Skew |tPHL - tPLH| (Note 1) 200 ns Receiver Skew |tPHL - tPLH| 50 ns TA= +25°C, VCC= 5V, RL= 3kΩto 7kΩ, Transition-Region Slew Rate CL= 500pF to 1000pF, measured from 3 6 30 V/µs -3V to +3V or +3V to -3V Note 1: Transmitter skew is measured at the transmitter zero crosspoints. _______________________________________________________________________________________ 3

+5V, 1µA, Single RS-232 Transceiver with AutoShutdown 1 Typical Operating Characteristics 2 (VCC= +5V, 250kbps data rate, 0.1µF capacitors, transmitter loaded with 3kW and CL, TA= +25°C, unless otherwise noted.) 2 X TRANSMITTER OUTPUT SLEW RATE vs. OPERATING SUPPLY VOLTAGE vs. LOAD CAPACITANCE LOAD CAPACITANCE CURRENT vs. LOAD CAPACITANCE A 10 50 50 M GE (V) 86 20kbps MAX221-01 40 MAX221-02 40 MAX221-03 ANSMITTER OUTPUT VOLTA ---204624 20kbps 12102k0bkpbsps 225500kkbbppss mSLEW RATE (V/s) 123000 +SLE-WSLEW SUPPLY CURRENT (mA) 123000 250kbps R T -8 120kbps 20kbps -10 0 0 0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 LOAD CAPACITANCE (pF) LOAD CAPACITANCE (pF) LOAD CAPACITANCE (pF) Pin Description PIN NAME FUNCTION Receiver Enable Control. Drive low for normal operation. Drive high to force the receiver output 1 EN (ROUT) into a high-impedance state. 2 C1+ Positive Terminal of the Voltage Doubler Charge-Pump Capacitor 3 V+ Positive Voltage Generated by the Charge Pump 4 C1- Negative Terminal of the Voltage Doubler Charge-Pump Capacitor 5 C2+ Positive Terminal of the Inverting Charge-Pump Capacitor 6 C2- Negative Terminal of the Inverting Charge-Pump Capacitor 7 V- Negative Voltage Generated by the Charge Pump 8 RIN RS-232 Receiver Input 9 ROUT TTL/CMOS Receiver Output Output of the Invalid Signal Detector. INVALIDis pulled low if no valid RS-232 level is present on 10 INVALID the receiver input. 11 TIN TTL/CMOS Transmitter Input Drive high to override automatic circuitry, keeping transmitter and charge pump on. 12 FORCEON FORCEOFFmust be high (Table 1). 13 TOUT RS-232 Transmitter Output 14 GND Ground 15 VCC +4.5V to +5.5V Supply Voltage Force-Off Input, active low. Drive low to shut down transmitter, receiver, and on-board charge 16 FORCEOFF pump. This overrides all automatic circuitry and FORCEON (Table 1). 4 _______________________________________________________________________________________

+5V, 1µA, Single RS-232 Transceiver with AutoShutdown three-state output and can be active or inactive. In shut- M +5V ISHDN down (FORCEOFF = low) or in AutoShutdown, the CBYPASS 0.1m 2F C1+ VC 1C5 3 C0.31m F rrimeeccpeeeiivvdeearrn icinse aaw chhtiivgeenh -(itmThaepb eMldeA a1Xn)c2. e2D 1sr itviaset e inE. NTshhheui tgrdehoc wteoniv pe(rFla OicseR h CtighEeh- AX C1 V+ 2 0.1m F 4 OFF= low). C1- 2 MAX221 The MAX221’s INVALID output is pulled low when no 5 C2+ V- 7 C4 valid RS-232 signal level is detected on the receiver 1 0.1 mC2F 6 C2- 0.1m F input. INVALID is functional in any mode (Figures 2 and 3). 11 TIN TOUT 13 AutoShutdown 3k 9 ROUT RIN 8 The MAX221 achieves 1µA supply current with Maxim’s AutoShutdown feature, which operates when FORCEON 5k is low and FORCEOFF is high. When the device senses no valid signal levels on the receiver input for 30µs, the TO POWER- on-board charge pump and driver are shut off, reducing 1 10 EN INVALID MANAGEMENT supply current to 1µA. This occurs if the RS-232 cable is UNIT disconnected or the connected peripheral transmitter is 12 FORCEON FORCEOFF 16 turned off. The MAX221 turns on again when a valid GND level is applied to the RS-232 receiver input. As a result, 14 the system saves power without changes to the existing BIOS or operating system. Figure 1. Shutdown Current Test Circuit Table 1 and Figure 2c summarize the MAX221 operat- _______________Detailed Description ing modes. FORCEON and FORCEOFF override AutoShutdown. When neither control is asserted, the Dual Charge-Pump Voltage Converter device selects between these states automatically, The MAX221’s internal power supply consists of a dual based on the receiver input level. Figures 2a, 2b, and charge pump that provides a positive output voltage 3a depict valid and invalid RS-232 receiver levels. (doubling charge pump) and a negative voltage (invert- Figure 3 shows the input levels and timing diagram for ing charge pump) from a single +5V supply. The AutoShutdown operation. charge pumps operate in continuous mode. Each A device or another system with AutoShutdown con- charge pump requires a flying capacitor (C1, C2) and a nected to the MAX221 may need time to wake up. reservoir capacitor (C3, C4) to generate the V+ and V- Figure 4 shows a circuit that forces the transmitter on supplies. for 100ms, allowing enough time for the other system to realize that the MAX221 is awake. If the other system RS-232 Transmitter transmits valid RS-232 signals within that time, the RS- The transmitter is an inverting level translator that con- 232 ports on both systems remain enabled. verts CMOS-logic levels to 5.0V EIA/TIA-232 levels. It guarantees a 250kbps data rate with worst-case loads When shut down, the device’s charge pumps are off, of 3kΩin parallel with 1000pF. V+ is pulled to VCC, V- is pulled to ground, and the transmitter output is high impedance. The time required When FORCEOFF is driven to ground, or when the to exit shutdown is typically 100µs (Figure 3b). AutoShutdown circuitry senses invalid voltage levels on the receiver input, the transmitter is disabled and the out- Software-Controlled Shutdown put is forced into a high-impedance state. The transmitter For direct software control, use INVALID to indicate a input does not have a pull-up resistor. DTR or Ring Indicator signal. Connect FORCEOFF and FORCEON together to disable AutoShutdown so the RS-232 Receiver line acts like a SHDNinput. The MAX221’s receiver converts RS-232 signals to CMOS-logic output levels. The receiver has an inverting _______________________________________________________________________________________ 5

+5V, 1µA, Single RS-232 Transceiver with AutoShutdown 1 Table 1. Output Control Truth Table 2 VALID 2 OPERATION FORCEON FORCEOFF EN RECEIVER TOUT ROUT X STATUS LEVEL A X 0 0 X High-Z Active Shutdown M (Forced Off) X 0 1 X High-Z High-Z 1 1 0 X Active Active Normal Operation (Forced On) 1 1 1 X Active High-Z 0 1 0 Yes Active Active Normal Operation (AutoShutdown) 0 1 1 Yes Active High-Z 0 1 0 No High-Z Active Shutdown (AutoShutdown) 0 1 1 No High-Z High-Z X = Don’t care FORCEOFF +0.3V POWER DOWN FORCEON TO MAX221 POWER SUPPLY INVALID RIN 30µs AND TRANSMITTER COUNTER INVALID R -0.3V INVALID IS AN INTERNALLY GENERATED SIGNAL USED BY THE AUTOSHUTDOWN LOGIC AND APPEARS AS AN OUTPUT. * TRANSMITTER IS DISABLED, REDUCING SUPPLY CURRENT TO 1m A IF RECEIVER INPUT IS BETWEEN +0.3V AND -0.3V FOR AT LEAST 30m s. POWER DOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE OPERATIONAL STATUS OF THE TRANSMITTER AND POWER SUPPLIES. Figure 2a. Entering 1µA Supply Mode via AutoShutdown Figure 2c. AutoShutdown Logic Table 2. INVALID Truth Table +2.7V RS-232 SIGNAL PRESENT INVALIDOUTPUT AT RECEIVER INPUT TO MAX221 RIN 30µs POWER SUPPLY Yes High COUNTER INVALID R No Low -2.7V * TRANSMITTER IS ENABLED IF: RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V; RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR LESS THAN 30m s. Figure 2b. Transmitter Enabled Using AutoShutdown 6 _______________________________________________________________________________________

+5V, 1µA, Single RS-232 Transceiver with AutoShutdown Applications Information M Using INVALID A TRANSMITTER ENABLED, INVALID HIGH INVALID indicates when an RS-232 signal is present at X the receiver input, and therefore when the port is in use. EL +2.7V INVALID can be used in alternative shutdown control 2 LEV INDETERMINATE schemes where it relieves the processor from constantly 2 T PU +0.3V polling the port for activity. 1 VER IN 0 AUT1OmSAH SUUTPDPOLWYN C,U TRRRAENNSTM, IITNTVEARL IDDI SLAOBWLED, Capacitor Selection EI -0.3V C The capacitor type used for C1–C4 is not critical for E R INDETERMINATE proper operation; either polarized or nonpolarized -2.7V capacitors are acceptable. If polarized capacitors are used, connect polarity as shown in the Typical Operating TRANSMITTER ENABLED, INVALID HIGH Circuit. The charge pump requires 0.1µF capacitors. Increasing the capacitor values (e.g., by a factor of 2) a) reduces ripple on the transmitter output and slightly reduces power consumption. C2, C3, and C4 can be increased without changing C1’s value. However, do not increase C1’s value without also increasing the values of RECEIVER C2, C3, and C4 to maintain the proper ratios (C1 to the INPUT INVALID other capacitors). VOLTAGE REGION (V) When using the minimum 0.1µF capacitors, make sure the capacitance does not degrade excessively with temperature. If in doubt, use capacitors with a larger VCC nominal value. The capacitor’s equivalent series resis- INVALID tance (ESR) usually rises at low temperatures and influ- OUTPUT ences the amount of ripple on V+ and V-. (V) 0 tINVL tINVH Power-Supply Decoupling tWU In most circumstances, a 0.1µF VCC bypass capacitor is adequate. In applications that are sensitive to power- V+ supply noise, use a capacitor of the same value as the VCC 0 charge-pump capacitor C1. Connect bypass capaci- tors as close to the IC as possible. V- Transmitter Output when b) Exiting Shutdown Figure 5 shows the transmitter output when exiting shut- Figure 3. AutoShutdown Trip Levels down mode. The transmitter is loaded with 3kΩ in paral- lel with 2500pF. The transmitter output displays no ringing or undesirable transients as the MAX221 comes out of shutdown. Note that the transmitter is enabled only POWER- MASTER SHDN LINE MANAGEMENT when the magnitude of V- exceeds approximately 3V. UNIT 0.1µF 1MW High Data Rates The MAX221 maintains the RS-232 ±5.0V minimum FORCEOFF FORCEON transmitter output voltage even at high data rates. Figure 6 shows a transmitter loopback test circuit. MAX221 Figure 7 shows the loopback test result at 120kbps, and Figure 8 shows the same test at 250kbps. Figure 4. AutoShutdown with Initial Turn-On to Wake Up a Mouse or Another System _______________________________________________________________________________________ 7

+5V, 1µA, Single RS-232 Transceiver with AutoShutdown 1 2 2 FORCEON = 5V/div TIN 5V/div FORCEOFF X TIN = GND A M 5V/div TOUT 5V/div TOUT TIN = VCC 5V/div ROUT 50m s/div 2m s/div Figure 5. Transmitter Output Exiting Shutdown or Figure 7. Loopback Test Result at 120kbps Powering Up +5V 0.1m F 5V/div TIN C3 C1+ VCC V+ C1 C1- 5V/div TOUT MAX221 C2+ V- C2 C4 C2- 5V/div ROUT TIN TOUT ROUT RIN 2m s/div EN Figure 8. Loopback Test Result at 250kbps 0V 5k 1000pF VCC FORCEOFF FORCEON GND INVALID ___________________Chip Information Figure 6. Loopback Test Circuit TRANSISTOR COUNT: 157 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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