19-1561; Rev 1; 10/99 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones A proprietary low-dropout transmitter output stage enables true RS-232 performance from a +3.0V to +5.5V supply with a dual charge pump. The charge pump requires only four small 0.1µF capacitors for operation from a +3.3V supply. The MAX3387E is capable of running at data rates up to 250kbps while maintaining RS-232 compliant output levels. The MAX3387E has a unique VL pin that allows interoperation in mixed-logic voltage systems. Both input and output logic levels are pin programmable through the VL pin. The MAX3387E is available in a space-saving TSSOP package. Features ♦ VL Pin for Compatibility with Mixed-Voltage Systems ♦ ±15kV ESD Protection on Rx Inputs and Tx Outputs ♦ Low 300µA Supply Current ♦ Guaranteed 250kbps Data Rate ♦ 1µA AutoShutdown Plus™ with Receivers Active ♦ Meets EIA/TIA-232 Specifications Down to 3.0V Ordering Information PART TEMP. RANGE MAX3387ECUG 0°C to +70°C 24 TSSOP MAX3387EEUG -40°C to +85°C 24 TSSOP Typical Operating Circuit Applications Subnotebook/Palmtop Computers PDAs and PDA Cradles +3.3V CBYPASS Cell Phone Data Cables Battery-Powered Equipment C1 0.1µF Hand-Held Equipment Peripherals C2 0.1µF Pin Configuration C1+ 1 24 FORCEOFF V+ 2 23 VCC C1- 3 22 GND C2+ 4 C2- 5 TTL/CMOS INPUTS 3 V- 6 T1IN 7 18 R1IN T2IN 8 17 R2IN INVALID 9 16 R3IN VL V+ 2 C3 0.1µF C1- MAX3387E C2+ V- 6 C2- 7 T1IN T1OUT 21 8 T2IN T2OUT 20 10 T3IN T3OUT 19 C4 0.1µF RS-232 OUTPUTS VL R1IN 18 20 T2OUT 19 T3OUT T3IN 10 5 15 VCC 14 R1OUT 21 T1OUT MAX3387E 23 24 FORCEOFF 1 C1+ 4 TOP VIEW PIN-PACKAGE VL TTL/CMOS OUTPUTS 13 R2OUT 5k R2IN 17 RS-232 INPUTS 5k VL 12 R3OUT R3IN 16 INVALID 5k 15 VL FORCEON 11 14 R1OUT R3OUT 12 13 R2OUT 9 FORCEON 11 GND 22 TSSOP 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 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX3387E General Description The MAX3387E 3V powered EIA/TIA-232 and V.28/V.24 is a communications interface with low power requirements, high data-rate capabilities, and enhanced electrostatic discharge (ESD) protection. The MAX3387E has three receivers and three transmitters. All RS-232 inputs and outputs are protected to ±15kV using the IEC 1000-4-2 Air-Gap Discharge method, ±8kV using the IEC 1000-4-2 Contact Discharge method, and ±15kV using the Human Body Model. MAX3387E 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones ABSOLUTE MAXIMUM RATINGS VCC to GND ..............................................................-0.3V to +6V VL to GND...................................................-0.3V to (VCC + 0.3V) V+ to GND ................................................................-0.3V to +7V V- to GND .................................................................+0.3V to -7V V+ + V-(Note 1) .............................................................. +13V Input Voltages T_IN, FORCEON, FORCEOFF to GND ..................-0.3V to +6V R_IN to GND .....................................................................±25V Output Voltages T_OUT to GND...............................................................±13.2V R_OUT........................................................-0.3V to (VL + 0.3V) Short-Circuit Duration T_OUT to GND........................Continuous Continuous Power Dissipation (TA = +70°C) 24-Pin TSSOP (derate 7.8mW/°C above +70°C) ..........625mW Operating Temperature Ranges MAX3387ECUG ...................................................0°C to +70°C MAX3387EEUG ................................................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10sec) .............................+300°C Note 1: V+ and V- can have maximum magnitudes of 7V, but their absolute difference cannot exceed 13V. 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. DC ELECTRICAL CHARACTERISTICS (VCC = VL = +3.0V to +5.5V; C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2–C4 = 0.33µF, tested at +5.0V ±10%; TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VL = +3.3V, TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC CHARACTERISTICS (VCC = +3.3V or +5V, TA = +25°C) Supply Current, AutoShutdown Plus All R_IN idle, FORCEON = GND, FORCEOFF = VCC, all T_IN idle 1.0 10 µA Supply Current FORCEOFF = FORCEON = VCC, no load 0.3 1 mA LOGIC INPUTS Input Logic Threshold Low Input Logic Threshold High T_IN, FORCEON, FORCEOFF T_IN, FORCEON, FORCEOFF VL = 3.3V or 5.0V 0.8 VL = 2.5V 0.6 VL = 5.0V 2.4 VL = 3.3V 2.0 VL = 2.5V 1.4 VL = 1.8V V 0.9 Transmitter Input Hysteresis Input Leakage Current V 0.5 T_IN, FORCEON, FORCEOFF ±0.01 V ±1 µA 0.4 V RECEIVER OUTPUTS Output Voltage Low IOUT = 1.6mA Output Voltage High IOUT = -1mA VL 0.6 VL 0.1 V RECEIVER INPUTS Input Voltage Range -25 Input Threshold Low TA = +25°C Input Threshold High TA = +25°C 2 +25 VL = 5.0V 0.8 1.5 VL = 2.5V or 3.3V 0.6 1.2 V VL = 5.0V 1.8 2.4 VL = 2.5V or 3.3V 1.5 2.4 _______________________________________________________________________________________ V V 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones (VCC = VL = +3.0V to +5.5V; C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2–C4 = 0.33µF, tested at +5.0V ±10%; TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VL = +3.3V, TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN Input Hysteresis TYP MAX UNITS 7 kΩ 0.5 Input Resistance TA = +25°C 3 5 V TRANSMITTER OUTPUTS Output Voltage Swing All transmitter outputs loaded with 3kΩ to ground ±5 ±5.4 Output Resistance VCC = V+ = V- = 0, transmitter output = ±2V 300 10M Output Short-Circuit Current VT_OUT = 0 ±60 mA Output Leakage Current VT_OUT = ±12V, transmitters disabled; VCC = 0 or 3.0V to 5.5V ±25 µA V Ω ESD PROTECTION R_IN, T_OUT ESD Protection Human Body Model ±15 IEC 1000-4-2 Air-Gap Discharge method ±15 IEC 1000-4-2 Contact Discharge method ±8 kV AutoShutdown Plus (FORCEON = GND, FORCEOFF = VCC) Receiver Input Threshold to INVALID Output High Figure 3a Receiver Input Threshold to INVALID Output Low Figure 3a INVALID Output Voltage Low IOUT = -1.6mA INVALID Output Voltage High IOUT = -1.0mA Positive threshold Negative threshold 2.7 -2.7 -0.3 V 0.3 V 0.4 V VL - 0.6 V Receiver Positive or Negative Threshold to INVALID High tINVH VCC = 5V, Figure 3b 1 µs Receiver Positive or Negative Threshold to INVALID Low tINVL VCC = 5V, Figure 3b 30 µs Receiver or Transmitter Edge to Transmitters Enabled tWU VCC = 5V, Figure 3b 100 µs Receiver or Transmitter Edge to tAUTOSHDN VCC = 5V, Figure 3b Transmitters Shutdown 15 30 60 sec _______________________________________________________________________________________ 3 MAX3387E DC ELECTRICAL CHARACTERISTICS (continued) MAX3387E 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones TIMING CHARACTERISTICS (VCC = VL = +3V to +5.5V; C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2–C4 = 0.33µF, tested at +5.0V ±10%; TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VL = +3.3V, TA = +25°C.) PARAMETER SYMBOL Maximum Data Rate Receiver Propagation Delay Time to Exit Shutdown Transmitter Skew Receiver Skew Transition-Region Slew Rate 4 CONDITIONS MIN RL = 3kΩ, CL = 1000pF, one transmitter switching tPHL tPLH MAX 250 CL = 150pF to 1000pF µs 0.15 VT_OUT > 3.7V tPHL - tPLH (Note 2) tPHL - tPLH UNITS kbps 0.15 Receiver input to receiver output, CL = 150pF VCC = 3.3V, TA = +25°C, RL = 3kΩ to 7kΩ, measured from +3V to -3V or -3V to +3V TYP 100 µs 100 ns 50 ns 6 30 V/µs CL = 150pF to 2500pF 4 _______________________________________________________________________________________ 30 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE DATA RATE = 250kbps LOAD = 3kΩ IN PARALLEL WITH CL 14 12 SLEW RATE (V/µs) 2.5 MAX3387E-02 5.0 OUTPUT VOLTAGE (V) SLEW RATE vs. LOAD CAPACITANCE 16 MAX3387E-01 7.5 0 -2.5 SLEW RATE 10 SLEW RATE + 8 6 4 -5.0 2 0 -7.5 1000 2000 3000 4000 0 5000 TRANSMITTER OUTPUT VOLTAGE vs. DATA RATE 3000 4000 LOAD = 3kΩ, 1000pF ONE TRANSMITTER SWITCHING AT DATA RATE, OTHER TRANSMITTERS AT 1/8 DATA RATE -2.5 LOAD = 3kΩ, ONE TRANSMITTER SWITCHING AT DATA RATE, OTHER TRANSMITTERS 250kbps AT 1/8 DATA RATE 50 SUPPLY CURRENT (mA) OUTPUT VOLTAGE (V) 5.0 0 2000 5000 SUPPLY CURRENT vs. LOAD CAPACITANCE 60 MAX3387E-03 7.5 2.5 1000 LOAD CAPACITANCE (pF) LOAD CAPACITANCE (pF) MAX3387E-04 0 40 120kbps 30 20 20kbps 10 -5.0 0 -7.5 0 50 100 150 DATA RATE (kbps) 200 250 0 1000 2000 3000 4000 5000 LOAD CAPACITANCE (pF) _______________________________________________________________________________________ 5 MAX3387E Typical Operating Characteristics (VCC = VL = +3.3V, TA = +25°C, unless otherwise noted.) 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones MAX3387E Pin Descriptions 6 PIN NAME FUNCTION 1 C1+ 2 V+ +5.5V Supply Generated by the Charge Pump 3 C1- Negative Terminal of the Voltage-Doubler Charge-Pump Capacitor 4 C2+ Positive Terminal of the Inverting Charge-Pump Capacitor 5 C2- Negative Terminal of the Inverting Charge-Pump Capacitor 6 V- 7 T1IN 8 T2IN 9 INVALID 10 T3IN 11 FORCEON 12 R3OUT 13 R2OUT 14 R1OUT 15 VL 16 R3IN 17 R2IN 18 R1IN 19 T3OUT 20 T2OUT 21 T1OUT 22 GND Ground 23 VCC +3.0V to +5.5V Supply Voltage 24 FORCEOFF Positive Terminal of the Voltage-Doubler Charge-Pump Capacitor -5.5V Generated by the Charge Pump TTL/CMOS Transmitter Inputs Output of the Valid Signal Detector. INVALID is high if a valid RS-232 signal is present on the receiver inputs. TTL/CMOS Transmitter Inputs Force-On Input. Drive high to override automatic circuitry keeping transmitters on (FORCEOFF must be high) (Table 1). TTL/CMOS Receiver Outputs. Swing between 0 and VL. Logic-Level Supply. All CMOS inputs and outputs are referenced to this supply. RS-232 Receiver Inputs RS-232 Transmitter Outputs Force-Off Input. Drive low to shut down transmitters and on-board power supply. This overrides all automatic circuitry and FORCEON (Table 1). _______________________________________________________________________________________ 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones Dual Charge-Pump Voltage Converter The MAX3387E’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 a +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 Transmitters These RS-232 output stages are turned off (high impedance) when the device is in shutdown mode. When the power is off, the MAX3387E permits the outputs to be driven up to ±12V. The transmitter inputs do not have pull-up resistors. Connect unused inputs to GND or VL. RS-232 Receivers The receivers convert RS-232 signals to CMOS-logic output levels. The MAX3387E’s receivers are always active, even when the device is in shutdown. The MAX3387E features an INVALID output that indicates when no signal is present on any RS-232 receiver inputs. INVALID is independent of other control logic functions; it indicates the receiver input conditions only (Figures 2 and 3). The transmitters are inverting level translators that convert CMOS-logic levels to 5.0V EIA/TIA-232 levels. The MAX3387E transmitters guarantee a 250kbps data rate with worst-case loads of 3kΩ in parallel with 1000pF, providing compatibility with PC-to-PC communication software (such as LapLink™). Transmitters can be paralleled to drive multiple receivers or mice. Figure 1 shows a complete system connection. +0.3V R_IN -0.3V POWERMANAGEMENT UNIT OR KEYBOARD CONTROLLER 30µs COUNTER R INVALID FORCEON FORCEOFF TRANSMITTERS ARE DISABLED, REDUCING SUPPLY CURRENT TO 1µA IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR AT LEAST 30µs. INVALID I/O CHIP POWER SUPPLY Figure 2a. INVALID Function Diagram, INVALID = Low VL VCC MAX3387E +2.7V I/O CHIP WITH UART R_IN RS-232 -2.7V 30µs COUNTER R INVALID CPU 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. Figure 2b. INVALID Function Diagram, INVALID = High Figure 1. Interface Under Control of PMU LapLink is a trademark of Traveling Software. _______________________________________________________________________________________ 7 MAX3387E Detailed Description T_IN R_IN TRANSMITTERS ENABLED, INVALID HIGH EDGE DETECT FORCEOFF S 30sec TIMER EDGE DETECT +2.7V AUTOSHDN R FORCEON RECEIVER INPUT LEVELS MAX3387E 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones INDETERMINATE +0.3V 0V AutoShutdown, TRANSMITTERS DISABLED, 1µA SUPPLY CURRENT, INVALID LOW -0.3V INDETERMINATE -2.7V TRANSMITTERS ENABLED, INVALID HIGH Figure 2c. AutoShutdown Plus Logic Figure 3a. Receiver Thresholds for INVALID FORCEOFF POWERDOWN FORCEON AUTOSHDN POWERDOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE OPERATIONAL STATUS OF THE TRANSMITTERS AND THE POWER SUPPLIES. Figure 2d. Power-Down Logic AutoShutdown Plus Mode The MAX3387E achieves a1µA supply current with Maxim’s AutoShutdown Plus feature, which operates when FORCEOFF is high and a FORCEON is low. When these devices do not sense a valid signal transition on any receiver and transmitter input for 30sec, the onboard charge pumps are shut down, reducing supply current to 1µA. This occurs if the RS-232 cable is disconnected or if the connected peripheral transmitters are turned off, and if the UART driving the transmitter inputs is inactive. The system turns on again when a valid transition is applied to any RS-232 receiver or transmitter input. As a result, the system saves power without changes to the existing BIOS or operating system. Figures 2a and 2b show valid and invalid RS-232 receiver voltage levels. INVALID indicates the receiver input’s condition, and is independent of FORCEON and 8 FORCEOFF states. Figure 2 and Table 1 summarize the MAX3387E’s operating modes. FORCEON and FORCEOFF override AutoShutdown Plus circuitry. When neither control is asserted, the IC selects between these states automatically based on the last receiver or transmitter input edge received. By connecting FORCEON to INVALID, the MAX3387E shuts down when no valid receiver level and no receiver or transmitter edge is detected for 30sec, and wakes up when a valid receiver level or receiver or transmitter edge is detected. By connecting FORCEON and FORCEOFF to INVALID, the MAX3387E shuts down when no valid receiver level is detected. A mouse or other system with AutoShutdown Plus 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 MAX3387E is awake. If the other system outputs valid RS-232 signal transitions within that time, the RS-232 ports on both systems remain enabled. VL Logic Supply Input Unlike other RS-232 interface devices where the receiver outputs swing between 0 and VCC, the MAX3387E features a separate logic supply input (VL) that sets VOH for the receiver outputs and sets thresholds for the receiver inputs. This feature allows a great deal of flexibility in interfacing to many different types of systems with different logic levels. Connect this input to the host logic supply (1.8V ≤ VL ≤ VCC). Also, see the Typical PDA/Cell-Phone Application section. _______________________________________________________________________________________ 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones MAX3387E RECEIVER INPUTS INVALID } REGION TRANSMITTER INPUTS TRANSMITTER OUTPUTS INVALID OUTPUT VCC tINVL tINVH 0 tAUTOSHDN tAUTOSHDN tWU tWU V+ VCC 0 V- Figure 3b. AutoShutdown Plus/INVALID Timing Diagram ±15kV ESD Protection POWERMANAGEMENT UNIT MASTER SHDN LINE 0.1µF 1M FORCEOFF FORCEON MAX3387E Figure 4. AutoShutdown with Initial Turn-On to Wake Up a System Software-Controlled Shutdown If direct software control is desired, INVALID can be used to indicate a DTR or ring indicator signal. Connect FORCEOFF and FORCEON together to bypass AutoShutdown so the line acts like a SHDN input. As with all Maxim devices, ESD-protection structures are incorporated on all pins to protect against electrostatic discharges (ESDs) encountered during handling and assembly. The MAX3387E driver outputs and receiver inputs have extra protection against static electricity. Maxim has developed state-of-the-art structures to protect these pins against ESD of ±15kV without damage. The ESD structures withstand high ESD in all states: normal operation, shutdown, and powered down. After an ESD event, Maxim’s “E” version devices keep working without latchup, whereas competing RS232 products can latch and must be powered down to remove latchup. ESD protection can be tested in various ways. The transmitter outputs and receiver inputs of this product family are characterized for protection to the following limits: 1) ±15kV using the Human Body Model 2) ±8kV using the Contact-Discharge method specified in IEC 1000-4-2 3) ±15kV using IEC 1000-4-2’s Air-Gap method _______________________________________________________________________________________ 9 MAX3387E 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones Table 1. Output Control Truth Table RECEIVER OR TRANSMITTER EDGE WITHIN 30sec T_OUT R_OUT FORCEON FORCEOFF VALID RECEIVER LEVEL Shutdown (Forced Off) X 0 X X High-Z Active Normal Operation (Forced On) 1 1 X X Active Active Normal Operation (AutoShutdown Plus) 0 1 X Yes Active Active Shutdown (AutoShutdown Plus) 0 1 X No High-Z Active Normal Operation INVALID 1 Yes X Active Active Normal Operation INVALID 1 X Yes Active Active Shutdown INVALID 1 No No High-Z Active Normal Operation (AutoShutdown) INVALID INVALID Yes X Active Active Shutdown (AutoShutdown) INVALID INVALID No X High-Z Active OPERATION STATUS X = Don’t care RC 1M CHARGE-CURRENT LIMIT RESISTOR RD 1500Ω IP 100% 90% DISCHARGE RESISTANCE Ir PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE) AMPERES HIGHVOLTAGE DC SOURCE Cs 100pF STORAGE CAPACITOR DEVICE UNDER TEST 36.8% 10% 0 0 Figure 5a. Human Body ESD Test Model tRL TIME tDL CURRENT WAVEFORM Figure 5b. Human Body Current Waveform ESD Test Conditions Human Body Model ESD performance depends on a variety of conditions. Contact Maxim for a reliability report that documents test setup, methodology, and results. Figure 5a shows the Human Body Model, and Figure 5b shows the current waveform it generates when discharged into a low impedance. This model consists of a 100pF capacitor charged to the ESD voltage of interest, which is then discharged into the test device through a 1.5kΩ resistor. 10 ______________________________________________________________________________________ 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones HIGHVOLTAGE DC SOURCE Cs 150pF I 100% DISCHARGE RESISTANCE STORAGE CAPACITOR 90% DEVICE UNDER TEST I PEAK CHARGE-CURRENT LIMIT RESISTOR RD 330Ω MAX3387E RC 50M to 100M 10% Figure 6a. IEC 1000-4-2 ESD Test Model IEC 1000-4-2 The IEC 1000-4-2 standard covers ESD testing and performance of finished equipment; it does not specifically refer to ICs. The MAX3387E helps you design equipment that meets Level 4 (the highest level) of IEC 1000-4-2, without the need for additional ESD-protection components. The major difference between tests done using the Human Body Model and IEC 1000-4-2 is higher peak current in IEC 1000-4-2 because series resistance is lower in the IEC 1000-4-2 model. Hence, the ESD withstand voltage measured to IEC 1000-4-2 is generally lower than that measured using the Human Body Model. Figure 6a shows the IEC 1000-4-2 model, and Figure 6b shows the current waveform for the ±8kV IEC 1000-4-2 Level 4 ESD Contact Discharge test. The air-gap test involves approaching the device with a charged probe. The contact-discharge method connects the probe to the device before the probe is energized. Machine Model The Machine Model for ESD tests all pins using a 200pF storage capacitor and zero discharge resistance. Its objective is to emulate the stress caused by contact that occurs with handling and assembly during manufacturing. All pins require this protection during manufacturing, not just RS-232 inputs and outputs. Therefore, after PC board assembly, the Machine Model is less relevant to I/O ports. __________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- t R = 0.7ns to 1ns t 30ns 60ns Figure 6b. IEC 1000-4-2 ESD Generator Current Waveform Table 2. Minimum Required Capacitor Values VCC (V) C1 (µF) C2, C3, C4 (µF) 3.0 to 3.6 0.1 0.1 4.5 to 5.5 0.047 0.33 3.0 to 5.5 0.22 1 tors for 3.3V operation. For other supply voltages, see Table 2 for required capacitor values. Do not use values smaller than those listed in Table 2. 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 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 V+ and V-. ______________________________________________________________________________________ 11 MAX3387E 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones Power-Supply Decoupling Operation Down to 2.7V 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. Transmitter outputs will meet EIA/TIA-562 levels of ±3.7V with supply voltages as low as +2.7V. 5V/div T2 2V/div Transmitter Outputs when Exiting Shutdown Figure 7 shows two transmitter outputs when exiting shutdown mode. As they become active, the two transmitter outputs are shown going to opposite RS-232 levels (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. High Data Rates T1 VCC = 3.3V C1–C4 = 0.1µF 50µs/div Figure 7. Transmitter Outputs when Exiting Shutdown The MAX3387E maintains 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 250kbps. For Figure 9, all transmitters were driven simultaneously at 120kbps into RS-232 loads in parallel with 1000pF. For Figure 10, a single transmitter was driven at 250kbps, and all transmitters were loaded with an RS-232 receiver in parallel with 1000pF. Interconnection with 3V and 5V Logic VCC 0.1µF VCC C1+ C1 C1- V+ C3 MAX3387E C2+ The MAX3387E can directly interface with various 5V logic families, including ACT and HCT CMOS. The logic voltage power-supply pin (VL) sets the output voltage level of the receivers and the input thresholds of the transmitters. VC4 C2 C2- T_ OUT T_ IN R_ IN R_ OUT 5k FORCEOFF VCC FORCEON 5V/div T1IN GND 5V/div T1OUT 1000pF 5V/div R1OUT VCC = 3.3V 2µs/div Figure 8. Loopback Test Circuit 12 Figure 9. Loopback Test Results at 120kbps ______________________________________________________________________________________ 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones 5V/div T1OUT 5V/div 5V/div R1OUT VCC = 3.3V 2µs/div Figure 10. Loopback Test Results at 250kbps Typical PDA/Cell-Phone Application The MAX3387E is designed with PDA applications in mind. Two transmitters and two receivers handle standard full-duplex communication protocol, while an extra transmitter allows a ring indicator signal to alert the UART on the PC. Without the ring indicator transmitter, solutions for these applications would require softwareintensive polling of the cradle inputs. Chip Information TRANSISTOR COUNT: 1267 ______________________________________________________________________________________ 13 MAX3387E T1IN The ring indicate (RI) signal is generated when a PDA, phone, or other “cradled” device is plugged into its cradle. This generates a logic-low signal to the RI transmitter input, creating +6V at the ring indicate pin. The PC’s UART RI input is the only pin that can generate an interrupt from signals arriving through the RS-232 port. The interrupt routine for this UART will then service the RS232 full-duplex communication between the PDA and the PC. As cell phone design becomes more like that of PDAs, cell phones will require similar docking ability and communication protocol. Cell phones operate on a single lithium-ion (Li+) battery and work with a power-supply voltage of +2.7V to +4V. The baseband logic coming from the phone connector can be as low as 1.8V at the transceivers. To prevent forward biasing of a device internal to the cell phone, the MAX3387E comes with a logic power-supply pin (VL) that limits the logic levels presented to the phone. The receiver outputs will sink to zero for low outputs, but will not exceed VL for logic highs. The input logic levels for the transmitters are also altered, scaled by the magnitude of the VL input. The device will work with V L as low as 1.8V before the charge-pump noise will begin to cause the transmitter outputs to oscillate. This is useful with cell phones and other power-efficient devices with core logic voltage levels that go as low as 1.8V. MAX3387E 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones TSSOP.EPS Package Information 14 ______________________________________________________________________________________ 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones MAX3387E NOTES ______________________________________________________________________________________ 15 MAX3387E 3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones NOTES 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. 16 ____________________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.