19-1253; Rev ; 8/97 3 to 5.5, up to 25kbps True RS-232 Transceiver General Description The MAX332 combines a microprocessor (µp) supervisory circuit with an RS-232 transceiver. The power-on reset performs a single function: it asserts a reset signal whenever the CC supply voltage declines below a preset threshold, staying asserted for at least 1ms after CC rises above the reset threshold. The MAX332 has an active-low RESET output, which is guaranteed to be in the correct state for CC down to 1. The reset comparator is designed to ignore fast transients on CC. Reset thresholds suitable for operation with a variety of supply voltages are available. The MAX332 transceivers have a proprietary lowdropout transmitter output stage, enabling true RS-232 performance with a dual charge pump powered from a +3 to +5.5 supply. The device requires only four small.1µf external charge-pump capacitors, and is guaranteed to run at data rates of up to 25kbps. It comes in the space-saving 2-pin SSOP package. Applications Palmtop Computers Portable/Battery-Powered Equipment Hand-Held Equipment Peripherals Printers Features Precise Monitoring of 5 and 3.3 Power- Supply oltages: 1ms (min) Power-On RESET Pulse Width Power-Supply Transient Immunity Guaranteed RESET alid to CC = 1 4µA Supply Current Achieved with AutoShutdown Plus Receivers Always Active Power-On Reset Always Active 4µA Low-Power Shutdown 25kbps Guaranteed Data Rate Ordering Information PART* TEMP. RANGE PIN-PACKAGE MAX332_CAP MAX332_EAP C to +7 C -4 C to +85 C 2 SSOP 2 SSOP * This part offers a choice of reset threshold voltage. From the table below, select the suffix corresponding to the desired threshold and insert it into the blank to complete the part number. Pin Configuration TOP IEW + C2+ C2-1 2 3 2 19 18 C1+ CC C1- SUFFIX A RESET THRESHOLD () 4.25 B 2.85 L 4.63 T 3.8 - T1IN 4 5 MAX332 MAXxxx 17 16 GND T1OUT T2IN 6 15 T2OUT Typical Operating Circuit appears at end of data sheet. R1OUT 7 14 R1IN R2OUT 8 13 R2IN INALID 9 12 RESET 1 11 SSOP AutoShutdown Plus is a trademark of Maxim Integrated Products. Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-8-998-88. For small orders, phone 48-737-76 ext. 3468.
3 to 5.5, up to 25kbps True RS-232 Transceiver ABSOLUTE MAXIMUM RATINGS CC...-.3 to 6 + (Note 1)...-.3 to 7 - (Note 1)...3 to -7 + + - (Note 1)...13 Input oltages T_IN,,...-.3 to 6 R_IN...±25 Output oltages T_OUT...±13.2 R_OUT, INALID, RESET...-.3 to ( CC +.3) 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 Short-Circuit Duration T_OUT...Continuous Continuous Power Dissipation (T A = +7 C) SSOP (derate 8.mW/ C above +7 C)...64mW Operating Temperature Ranges MAX332_CAP... C to +7 C MAX332_EAP...-4 C to +85 C Storage Temperature Range...-65 C to +16 C Lead Temperature (soldering, 1sec)...+3 C Note 1: + and - can have a magnitude of +7 (max), but their absolute difference cannot exceed +13. ( CC = 3 to 5.5, C1 C4 =.1µF (tested at 3.3 ±1%), C1 =.47µF, C2 C4 =.33µF (tested at 5 ±1%), T A = T MIN to T MAX, unless otherwise noted. Typical values are at T A = +25 C.) PARAMETER DC CHARACTERISTICS Power-Supply Current Shutdown Supply Current AutoShutdown Plus Supply Current Input Leakage Current Input Hysteresis Output oltage Low Output oltage High RECEIER INPUTS Input oltage Range Input Threshold Low Input Threshold High Input Hysteresis Input Resistance Receiver Input Threshold to INALID Output High Receiver Input Threshold to INALID Output Low INALID Output oltage Low No load, CC = 3.3 or 5, T A = +25 C = GND, T A = +25 C All R_IN unconnected, = GND, = CC, all T_IN = CC or GND, T A = +25 C LOGIC INPUTS AND RECEIER OUTPUTS Input Logic Threshold Low T_IN,, Input Logic Threshold High INALID OUTPUT T_IN,, CC = 3.3 2. CC = 5 2.4 T_IN,, T_IN,, I OUT = 1.6mA I OUT = -1mA CC = 3.3 CC = 5 CC = 3.3 CC = 5 T A = +25 C Figure 3, positive threshold Figure 3, negative threshold Figure 3 I OUT = 1.6mA CONDITIONS MIN TYP MAX CC - CC -.6.1-25 25.6 1.2.8 1.5 3 5 7-2.7.45 1. 4. 1 4. 1 ±.1 ±1. 25 1.5 2.4 1.8 2.4.3.8.4 2.7 -.3.3.4 UNITS ma µa µa µa m kω 2
3 to 5.5, up to 25kbps True RS-232 Transceiver ELECTRICAL CHARACTERISTICS (continued) ( CC = 3 to 5.5, C1 C4 =.1µF (tested at 3.3 ±1%), C1 =.47µF, C2 C4 =.33µF (tested at 5 ±1%), T A = T MIN to T MAX, unless otherwise noted. Typical values are at T A = +25 C.) PARAMETER INALID Output oltage High Receiver Positive or Negative Threshold to INALID High Receiver Positive or Negative Threshold to INALID Low Receiver or Transmitter Edge to Transmitters Enabled Receiver or Transmitter Edge to Shutdown Output oltage Swing Output Resistance Output Short-Circuit Current Output Leakage Current Figure 3 Figure 3 Figure 5 Figure 3 CONDITIONS All transmitter outputs loaded with 3kΩ to ground CC = + = - = GND, T_OUT = ±2 T_OUT = GND, T_IN = CC or GND T_OUT = ±12, CC = to 5.5, transmitters disabled MIN TYP MAX.1 9 µs 25 15 3 6 ±5. ±5.4 3 1M ±35 ±6 RESET Operating oltage MAX332_C 1. 5.5 Range MAX332_E 1.2 5.5 RESET Threshold RESET Output oltage I OUT = -1mA AUTOSHUTDOWN PLUS ( = GND, = CC) TRANSMITTER OUTPUTS RESET OUTPUT MAX332A MAX332B MAX332L MAX332T I SINK = 1.2mA, CC = reset threshold, MAX332B/T I SINK = 3.2mA, CC = reset threshold, MAX332A/L I SINK = 5µA, CC > 1, MAX332_C I SINK = 1µA, CC > 1.2, MAX332_E CC -.6 ±25 4. 4.25 4.5 2.7 2.85 3. 4.5 4.63 4.75 3. 3.8 3.15.3.4.3.4 UNITS µs µs sec Ω ma µa 3
3 to 5.5, up to 25kbps True RS-232 Transceiver TIMING CHARACTERISTICS ( CC = 3 to 5.5, C1 C4 =.1µF, C1 C4 =.1µF (for 3.3 ±1%), C1 =.47µF, C2 C4 =.33µF (tested at 5 ±1%), T A = T MIN to T MAX, unless otherwise noted. Typical values are at T A = +25 C.) Maximum Data Rate Receiver Propagation Delay Transmitter Skew Receiver Skew PARAMETER Transition-Region Slew Rate R L = 3kΩ, C L = 1pF, one transmitter switching R_IN to R_OUT, C L = 15pF t PHL - t PLH t PHL - t PLH CONDITIONS CC = 3.3, R L = 3kΩ to 7kΩ, measured from +3 to -3 or -3 to +3, T A = +25 C t PHL t PLH C L = 15pF to 1pf C L = 15pF to 25pf MIN TYP MAX 25.3.3 1 2 6 3 4 3 UNITS kbps µs ns ns /µs CC to RESET Delay 1m overdrive from reset threshold 4 µs RESET Active Timeout Period CC = reset threshold 1 28 ms Typical Operating Characteristics OUTPUT OLTAGE () ( CC = 3.3, 25kbps data rate, C1 C4 =.1µF, all transmitters loaded with 3kΩ. Typical values are at T A = +25 C, unless otherwise noted.) 7.5 5. 2.5-2.5-5. -7.5 TRANSMITTER OUTPUT OLTAGE vs. LOAD CAPACITANCE T_OUT+ ONE TRANSMITTER AT 25kbps ONE TRANSMITTER AT 15.6kbps LOAD = 3kΩ + C L T_OUT- 1 2 3 4 5 LOAD CAPACITANCE (pf) MAX332 TOC1 SLEW RATE (/us) 12 1 8 6 4 2 SLEW RATE vs. LOAD CAPACITANCE NEGATIE SLEW POSITIE SLEW ONE TRANSMITTER AT 25kbps ONE TRANSMITTER AT 15.6kbps LOAD = 3kΩ + C L 1 2 3 4 5 LOAD CAPACITANCE (pf) MAX332 TOC2 SUPPLY CURRENT (ma) 45 4 35 3 25 2 15 1 5 SUPPLY CURRENT vs. LOAD CAPACITANCE WHEN TRANSMITTING DATA ONE TRANSMITTER AT FULL DATA RATE INDICATED ONE TRANSMITTER AT 1/16 DATA RATE INDICATED 25kbps 12kbps 2kbps 1 2 3 4 5 LOAD CAPACITANCE (pf) MAX332 TOC3 4
3 to 5.5, up to 25kbps True RS-232 Transceiver Typical Operating Characteristics (continued) ( CC = 3.3, 25kbps data rate, C1 C4 =.1µF, all transmitters loaded with 3kΩ. Typical values are at T A = +25 C, unless otherwise noted.) MAXIMUM TRANSIENT DURATION (µs) 3 25 2 15 1 5 MAXIMUM TRANSIENT DURATION vs. RESET COMPARATOR OERDRIE SHUTDOWN MODE NOT IN SHUTDOWN MODE C BYPASS =.1µF 1 1 1 RESET COMPARATOR OERDRIE (m) MAX332toc5 POWER-UP RESET DELAY 1.4 1.3 1.2 1.1 1..99.98.97.96 NORMALIZED POWER-UP RESET DELAY vs. TEMPERATURE -4-2 2 4 6 8 TEMPERATURE ( C) MAX332 TOC6 Pin Description PIN NAME FUNCTION 1 + 5.5 generated by the charge pump 2 C2+ Positive terminal of inverting charge-pump capacitor 3 C2- Negative terminal of inverting charge-pump capacitor 4 - -5.5 generated by the charge pump 5, 6 T_IN TTL/CMOS Transmitter Inputs (T1IN and T2IN) 7, 8 R_OUT TTL/CMOS Receiver Outputs (R1OUT and R2OUT) 9 INALID 1 RESET Output of the alid Signal Detector. Asserts when no valid RS-232 levels are present on any of the receiver inputs for 9µs. RESET Output. RESET remains low while CC is below the reset threshold, and for 28ms (max) after CC rises above the reset threshold. 11 12 13, 14 R_IN RS-232 Receiver Inputs (R2IN and R1IN) 15, 16 T_OUT RS-232 Transmitter Outputs (T2OUT and T1OUT) 17 GND Ground 18 C1- Negative terminal of voltage-doubler charge-pump capacitor 19 CC +3 to +5.5 Supply oltage Force-Off Input. Drive low to shut down transmitters and on-board power supply. This overrides AutoShutdown Plus and (Table 1). Force-On Input. Drive high to override AutoShutdown Plus, keeping transmitters on ( must be high) (Table 1). 2 C1+ Positive terminal of voltage-doubler charge-pump capacitor 5
3 to 5.5, up to 25kbps True RS-232 Transceiver Table 1. MAX332 Output Control Truth Table X 1 X = Don t Care *Time since last receiver or transmitter input activity AUTOSHUTDOWN PLUS* OPERATION STATUS T_OUT Shutdown X High-Z (forced off) R_OUT Active Normal operation 1 X Active Active (forced on) Normal operation 1 <3sec* Active Active (AutoShutdown Plus) Shutdown 1 >3sec* High-Z Active (AutoShutdown Plus) Detailed Description Dual Charge-Pump oltage Converter The MAX332 s internal power supply consists of a regulated dual charge pump that provides output voltages of +5.5 (doubling charge pump) and -5.5 (inverting charge pump) while CC remains in the 3 to 5.5 range. The charge pumps operate in discontinuous mode; they are enabled if the output voltages are less than 5.5, and disabled if output voltages exceed 5.5. Each charge pump requires a flying capacitor (C1, C2) and a reservoir capacitor (C3, C4) to generate the + and - supplies. RS-232 Transmitters The transmitters are inverting level translators that convert CMOS-logic levels to 5 EIA/TIA-232 levels. The MAX332 transmitters guarantee a 25kbps data rate with worst-case loads of 3kΩ in parallel with 1pF, providing compatibility with PC-to-PC communication software (such as LapLink ). Transmitters can be paralleled to drive multiple receivers. Figure 1 shows a complete system connection. When is driven to ground, the transmitter s outputs become high impedance. When the AutoShutdown Plus circuitry senses that all receiver and transmitter inputs are inactive for more than 3sec, the transmitters turn off and the outputs go into a highimpedance state, but the receivers remain active. When the power is off or the MAX332 is shut down, outputs may be driven up to ±12. The transmitter inputs do not have pull-up resistors. Connect unused inputs to GND or CC. Laplink is a trademark of Traveling Software. POWER- MANAGEMENT UNIT OR KEYBOARD CONTROLLER CPU INALID I/O CHIP WITH UART Figure 1. Interface Under Control of PMU MAX332 RS-232 RS-232 Receivers The receivers convert RS-232 signals to CMOS-logic output levels. All receivers have inverting outputs and are active in shutdown (Table 1). AutoShutdown Plus Mode Maxim s AutoShutdown Plus feature, which operates when is high and is low, achieves a 4µA supply current. When the MAX332 senses no valid signal levels on all receiver and transmitter inputs for 3sec, the on-board power supply and drivers shut off, T1 T2 R1 R2 6
3 to 5.5, up to 25kbps True RS-232 Transceiver reducing supply current to 4µA. This occurs if the RS-232 cable is disconnected or the connected peripheral transmitters turn off. The system turns on again when a valid transition occurs at any RS-232 receiver or transmitter input. As a result, the system saves power without changes to the existing BIOS or operating system. The INALID output is high when the receivers are active. Since INALID indicates the receiver inputs condition, it can be used in any mode (Figure 2). Tables 1 and 2 and Figure 2 summarize the MAX332 s operating modes. and override the automatic circuitry and force the transceiver into its normal operating state or into its low-power standby state. When neither control is asserted, the IC enters AutoShutdown Plus mode and selects between these states automatically, based on the last receiver or transmitter input edge received. When shut down, the device s charge pumps turn off, + decays to CC, - decays to ground, and the transmitter outputs turn off (high impedance). The time required to exit shutdown is typically 25µs (Figure 3a). +.3 R_IN -.3 9µs TIMER R INALID INALID ASSERTED IF BOTH RECEIER INPUTS ARE BETWEEN +.3 AND -.3 FOR AT LEAST 9µs. Figure 2a. INALID Functional Diagram, INALID Low +2.7 R_IN -2.7 9µs TIMER R INALID DEASSERTED IF EITHER RECEIER INPUT HAS BEEN BETWEEN +2.7 AND -2.7 FOR LESS THAN 9µs. INALID Software-Controlled Shutdown If direct software control is desired, use INALID to indicate DTR or Ring Indicator signal. Connect and together to bypass the AutoShutdown Plus feature so the line acts like a SHDN input. Power-On Reset In addition to issuing a reset to the microprocessor (µp) during power-up, power-down, and brownout conditions, the MAX332 is relatively immune to shortduration, negative-going CC transitions (glitches). Typically, a CC transient that goes 1m below the reset threshold and lasts 2µs or less does not cause a reset pulse (see Typical Operating Characteristics). Additional bypass capacitance mounted as close as possible to the CC pin provides additional transient immunity. Figure 2b. INALID Functional Diagram, INALID High T_IN R_IN EDGE DETECT EDGE DETECT Figure 2c. AutoShutdown Plus Logic S 3sec TIMER R AUTOSHDN POWERDOWN* Table 2. INALID Truth Table RS-232 SIGNAL PRESENT AT RECEIER INPUT Yes No INALID OUTPUT H L AUTOSHDN * POWERDOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE OPERATIONAL STATUS OF THE TRANSMITTERS AND THE POWER SUPPLIES. Figure 2d. Power-Down Logic 7
3 to 5.5, up to 25kbps True RS-232 Transceiver INALID OUTPUT RECEIER INPUTS OLTAGE TRANSMITTER INPUTS OLTAGE TRANSMITTER OUTPUTS OLTAGE CC + I NL * ** INALID REGION t AUTOSHDN t WU t AUTOSHDN t WU CC - * ALL RECEIER/TRANSMITTER INPUTS INACTIE ** ANY ONE RECEIER/TRANSMITTER INPUT BECOMES ACTIE = GND, = CC Figure 3a. AutoShutdown Plus and INALID Timing Diagram RECEIER INPUT LEELS 2.7.3 -.3-2.7 INALID HIGH INDETERMINATE INALID LOW INDETERMINATE INALID HIGH Figure 3b. Receiver Positive/Negative Thresholds for INALID Applications Information Ensuring a alid Reset Output Down to CC = When CC falls below 1, RESET no longer sinks current: it becomes an open circuit. Therefore, highimpedance CMOS logic inputs connected to RESET can drift to undefined voltages. This presents no problem in most applications, since most µps and other circuitry is inoperative with CC below 1. However, in applications where RESET must be valid down to, add a pull-down resistor to ground, holding RESET low (Figure 4). R1 s value is not critical; 1kΩ is large enough not to load RESET, and small enough to pull it to ground. Capacitor Selection The capacitor type used for C1 C4 is not critical for proper operation; use either polarized or nonpolarized capacitors. The charge pump requires.1µf capacitors for 3.3 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, C4, and CBYPASS, to maintain the proper ratios (C1 to the other capacitors). 8
3 to 5.5, up to 25kbps True RS-232 Transceiver GND MAX332 CC RESET When using the minimum required capacitor values, make sure the capacitor value does not degrade excessively with temperatures outside the C to +7 C range. If in doubt, use capacitors with a larger nominal value. The capacitor's equivalent series resistance (ESR), which usually rises at low temperatures, influences the amount of ripple on + and -. Transmitter Outputs when Exiting Shutdown Figure 5 shows two transmitter outputs when exiting shutdown mode. As they become active, the two transmitter outputs go to opposite RS-232 levels (one transmitter input is high; the other is low). Each transmitter is loaded with 3kΩ in parallel with 25pF. The transmitter outputs display no ringing or undesirable transients as they exit shutdown. Note that the transmitters are enabled only when the magnitude of - exceeds approximately 3. CC Figure 4. Ensuring RESET alid to CC = 1k 2/div 2/div CC = 3.3 C1 - C4 =.1µF 5µs/div = T2OUT T1OUT Figure 5. Transmitter Outputs when Exiting Shutdown or Powering Up CC C1 C2 C1+ C2- C1- C2+ T_ IN R_ OUT CC MAX332 + - T_ OUT R_ IN C3* C4 High Data Rates The MAX332 maintains the RS-232 ±5 minimum transmitter output voltage even at high data rates. Figure 6 shows a transmitter loop-back test circuit. Figure 7 shows a loop-back test result at 12kbps, and Figure 8 shows the same test at 25kbps. For Figure 7, both transmitters were driven simultaneously at 12kbps into RS-232 loads in parallel with 1pF. For Figure 8, a single transmitter was driven at 25kbps, and both transmitters were loaded with an RS-232 receiver in parallel with 1pF. Interconnection with 3 and 5 Logic The MAX332 can directly interface with various 5 logic families, including ACT and HCT CMOS. See Table 4 for more information on possible combinations of interconnections. CC *C3 CAN BE RETURNED TO CC OR GND. GND Figure 6. Loop-Back Test Circuit Table 3. Required Minimum Capacitance alues CC () 3 to 3.6 4.5 to 5.5 3 to 5.5 C1 (µf).1 5k.47.33.1.47 1pF C2, C3, C4, C BYPASS (µf).1 9
3 to 5.5, up to 25kbps True RS-232 Transceiver T1IN T1OUT R1IN R1OUT CC = 3.3 C1 - C4 =.1µF C LOAD = 1pF 2µs/div 5 5-5 5 T1IN T1OUT R1IN R1OUT CC = 3.3 C1 - C4 =.1µF C LOAD = 1pF 2µs/div 5 5-5 5 Figure 7. Loop-Back Test Result at 12kbps Figure 8. Loop-Back Test Result at 25kbps Table 4. Logic-Family Compatibility with arious Supply oltages SYSTEM POWER-SUPPLY OLTAGE () CC SUPPLY OLTAGE () COMPATIBILITY Chip Information TRANSISTOR COUNT: 1577 3.3 5 5 3.3 5 3.3 Compatible with all CMOS families Compatible with all TTL and CMOS families Compatible with ACT and HCT CMOS, and with AC, HC, or CD4 CMOS 1
3 to 5.5, up to 25kbps True RS-232 Transceiver Typical Operating Circuit CC +3.3 CC C1.1µF C2.1µF C1+ CC + C2- C1- C2+ T1IN T2IN.1µF MAX332 T1 T2 T1OUT T2OUT - C3*.1µF C4.1µF RS-232 OUTPUTS µp SYSTEM R1OUT AUTOSHUTDOWN PLUS R1 R1IN 5k RS-232 INPUTS R2OUT R2 R2IN RESET INPUT RESET 5k INALID GND *C3 MAY BE RETURNED TO EITHER CC OR GND. 11
3 to 5.5, up to 25kbps True RS-232 Transceiver Package Information SSOP.EPS 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. 12 Maxim Integrated Products, 12 San Gabriel Drive, Sunnyvale, CA 9486 48-737-76 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.