19-2667; Rev 1; 1/03 ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications The MAX3322E/MAX3323E 3.0V to 5.5V powered EIA/TIA-232 and V.28/V.24 communications interfaces are designed for multidrop applications with low power requirements, high data-rate capabilities, and enhanced electrostatic discharge (ESD) protection. 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. The MAX3322E/MAX3323E have pin-selectable 5kΩ/high-impedance RS-232 receivers. These devices are capable of receiving data in high-impedance mode. In multidrop applications, one receiver has a 5kΩ input resistance, while the other receivers are high impedance to ensure the RS-232 standard is observed. Logic control permits selection of the functional mode: high impedance or RS-232 standard load. The transmitters are enabled by logic control to allow the multiplexing of the inputs to a single UART. 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 MAX3322E/MAX3323E are capable of running at data rates up to 250kbps while maintaining RS-232-compliant output levels. The MAX3322E/MAX3323E have a unique VL pin that allows operation in mixed-logic voltage systems. Both input and output logic levels are pin programmable through the VL pin. The MAX3322E is a 2Tx/2Rx device for hardware handshaking in standard RS-232 mode, and the MAX3323E is a 1Tx/1Rx, required in most multidrop applications. The MAX3322E is offered in a space-saving TSSOP package. The MAX3323E is offered in 16-pin DIP and space-saving TSSOP packages. Applications Bar-Code Scanners Video Security Industrial Data Acquisition Data Splitters Features ♦ Pin-Selectable 5kΩ/High-Impedance Receivers ♦ Transmitter Outputs Three-Stated by Logic Control ♦ VL Pin for Compatibility with Mixed Voltage Systems ♦ 1Tx/1Rx (MAX3323E) or 2Tx/2Rx (MAX3322E) Versions ♦ 250kbps Data Rate ♦ 1µA Low-Power Shutdown ♦ High ESD Protection for RS-232 I/O Pins ±15kV—Human Body Model ±8kV—IEC 1000-4-2 Contact Discharge ±15kV—IEC 1000-4-2 Air-Gap Discharge Ordering Information PART TEMP RANGE PIN-PACKAGE MAX3322E EUP -40°C to +85°C 20 TSSOP MAX3323E EUE -40°C to +85°C 16 TSSOP MAX3323EEPE -40°C to +85°C 16 DIP Pin Configurations TOP VIEW C1+ 1 20 VCC V+ 2 19 GND C1- 3 18 SHDN C2+ 4 C2- 5 17 VL MAX3322E V- 6 16 RENABLE 15 TXENABLE TOUT2 7 14 TIN2 RIN2 8 13 ROUT2 TOUT1 9 12 TIN1 RIN1 10 11 ROUT1 TSSOP Typical Operating Circuit and Functional Diagram appear at end of data sheet. Pin Configurations continued at end of data sheet. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX3322E/MAX3323E General Description MAX3322E/MAX3323E ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications ABSOLUTE MAXIMUM RATINGS All Voltages Referenced to GND VCC, VL ....................................................................-0.3V to +6V V+ (Note 1) ....................................................(VCC - 0.3V) to +7V V- (Note 1) ................................................................+0.3V to -7V V+ + |V-| (Note 1) .................................................................+13V Input Voltages TIN_, RENABLE, TXENABLE, SHDN .....................-0.3V to +6V RIN_ ..................................................................................±25V Output Voltages TOUT_............................................................................±13.2V ROUT_........................................................-0.3V to (VL + 0.3V) Short-Circuit Duration TOUT_ to GND........................Continuous Continuous Power Dissipation (TA = +70°C) 16-Pin DIP (derate 10.5mW/°C above +70°C) ............842mW 16-Pin TSSOP (derate 9.4mW/°C above +70°C) ........755mW 20-Pin TSSOP(derate 11mW/°C above +70°C) ..........879mW Operating Temperature Range MAX3322E/MAX3323E ...................................-40°C to +85°C Junction Temperature ..................................................... +150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+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 = 3.0V to 5.5V, VL = 1.65V to 5.5V, C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2 = C3 = C4 = 0.33µF, tested at +5V ±10%; TA = TMIN to TMAX. Typical values are at VCC = VL = 3.3V and TA = +25°C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC CHARACTERISTICS Supply Current Normal Operation Supply Current in Shutdown ICC SHDN = VL, no load 1 ICC(SHDN) SHDN = 0V, no load 1 mA 10 µA 0.4 V TRANSMITTER LOGIC INPUTS Input Logic Threshold Low Input Logic Threshold High VL ≤ 1.8V VL - 0.4 VL > 1.8V 2/3 x VL Transmitter Input Hysteresis Input Leakage Current V 0.2 IIL ±0.01 V ±1 µA 0.4 V ±0.01 ±1 µA +0.05 +10 µA LOGIC INPUTS (TXENABLE, RENABLE, SHDN) Input Logic Threshold Low Input Logic Threshold High 2/3 x VL Input Leakage Current V RECEIVER OUTPUTS Output Leakage Current IOL Output Voltage Low VOL Output Voltage High VOH Receivers disabled, SHDN = 0V IOUT = 1.6mA, VL > 1.8V 0.4 IOUT = 1mA, VL ≤ 1.8V 0.4 IOUT = -1mA, VL > 1.8V VL - 0.4 VL - 0.1 IOUT = -500µA, VL ≤ 1.8V VL - 0.4 V V VL- 0.1 RECEIVER INPUTS Input Voltage Range Input Threshold Low 2 VRIN -25 +25 VL = 1.65V 0.25 0.6 VL = 3.3V 0.6 1.2 VL = 5.0V 0.8 1.5 _______________________________________________________________________________________ V V ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications (VCC = 3.0V to 5.5V, VL = 1.65V to 5.5V, C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2 = C3 = C4 = 0.33µF, tested at +5V ±10%; TA = TMIN to TMAX. Typical values are at VCC = VL = 3.3V and TA = +25°C, unless otherwise noted.) PARAMETER SYMBOL Input Threshold High CONDITIONS MIN TYP MAX VL = 1.65V 1 1.4 VL = 3.3V 1.5 2.4 VL = 5.0V 1.8 2.4 Input Hysteresis 0.35 Input Resistance RIN RENABLE = 1 3 RENABLE = 0 or SHDN = 0V, RIN from -13V to +13V 1 5 UNITS V V 7 kΩ MΩ TRANSMITTER OUTPUTS Output Voltage Swing All transmitter outputs loaded with 3kΩ to ground ±5 ±5.4 V Output Resistance VCC = V+ = V- = 0, TOUT_ = ±2V, TXENABLE = 1 300 10M Ω Output Short-Circuit Current VOUT = 0V ±60 mA Output Leakage Current VOUT = ±12V, transmitters disabled ±25 µA ESD PROTECTION RIN, TOUT Human Body Model ±15 IEC 1000-4-2 Air-Gap Discharge ±15 IEC 1000-4-2 Contact Discharge ±8 kV TIMING CHARACTERISTICS (VCC = 3.0V to 5.5V, VL = 1.65V to 5.5V, C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2 = C3 = C4 = 0.33µF, tested at +5V ±10%; TA = TMIN to TMAX. Typical values are at VCC = VL = 3.3V and TA = +25°C, unless otherwise noted.) PARAMETER SYMBOL RL = 3kΩ, CL = 1000pF, one transmitter switching Maximum Data Rate Receiver Propagation Delay CONDITIONS tPHL tPLH tPHL MIN TYP MAX 250 kbps 150 RIN_ to ROUT_, CL = 30pF, VL = 3.3V, Figure 2 UNITS ns 180 0.6 TIN_ to TOUT_, RL = 3kΩ, CL = 1000pF, Figure 1 0.7 Time to Enter Three-State on Tx (Note 2) 10 50 µs Time to Exit Three-State on Tx (Note 2) 3 50 µs Time to Enable Resistor (Note 2) 0.4 10 µs Time to Disable Resistor (Note 2) 0.2 10 Transmitter Propagation Delay tPLH µs µs Time to Enter Shutdown 50 µs Time to Exit Shutdown 50 µs Transmitter Skew 100 ns Receiver Skew 30 ns Transition Region Slew Rate RL = 3kΩ to 7kΩ, CL = 1000pF, measured from +3V to -3V or vice versa 6 30 V/µs Note 2: Guaranteed by design. Not production tested. _______________________________________________________________________________________ 3 MAX3322E/MAX3323E DC ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VCC = 3.3V, VL = 3.3V, C1–C4 = 0.1µF, TA = +25°C.) SLEW RATE vs. LOAD CAPACITANCE TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE 2.5 15 SLEW RATESLEW RATE (V/µs) DATA RATE = 250kbps LOAD = 3kΩ IN PARALLEL WITH CL 0 MAX3322E toc02 5.0 OUTPUT VOLTAGE (V) 18 MAX3322E toc01 7.5 -2.5 12 9 SLEW RATE+ 6 3 -5.0 0 -7.5 0 0 1000 2000 3000 4000 1000 5000 2000 3000 4000 5000 LOAD CAPACITANCE (pF) LOAD CAPACITANCE (pF) TRANSMITTER OUTPUT VOLTAGE vs. DATA RATE MAX3322E toc03 LOAD = 3kΩ, 1000pF ONE TRANSMITTER SWITCHING AT DATA RATE, OTHER TRANSMITTER AT 1/8 DATA RATE 2.5 0 SUPPLY CURRENT (mA) OUTPUT VOLTAGE (V) 5.0 40 -2.5 LOAD = 3kΩ ONE TRANSMITTER SWITCHING AT DATA RATE, OTHER TRANSMITTER AT 1/8 DATA RATE 30 250kbps MAX3322E toc04 SUPPLY CURRENT vs. LOAD CAPACITANCE 7.5 125kbps 20 40kbps 10 -5.0 -7.5 0 50 100 150 200 250 1000 2000 3000 4000 LOAD CAPACITANCE (pF) RECEIVER INPUT RESISTANCE vs. INPUT VOLTAGE RANGE RECEIVER INPUT RESISTANCE vs. INPUT VOLTAGE RANGE RENABLE = 1 5.25 5.00 4.75 4.50 5 5000 MAX3322E toc06 MAX3322E toc05 5.50 RENABLE = 0 VL = 5V 4 3 2 1 0 -25 -15 -5 VRIN (V) 4 0 DATA RATE (kbps) RECEIVER INPUT RESISTANCE (MΩ) 0 RECEIVER INPUT RESISTANCE (kΩ) MAX3322E/MAX3323E ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications 5 15 25 -25 -15 -5 5 15 VRIN (V) _______________________________________________________________________________________ 25 ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications PIN NAME FUNCTION MAX3322E MAX3323E 1 1 C1+ 2 2 V+ +5.5V Generated by the Charge Pump 3 3 C1- Negative Terminal of the Voltage-Doubler Charge-Pump Capacitor 4 4 C2+ Positive Terminal of the Inverting Charge-Pump Capacitor 5 5 C2- 6 6 V- 7, 9 7 TOUT_ Positive Terminal of the Voltage-Doubler Charge-Pump Capacitor Negative Terminal of the Inverting Charge-Pump Capacitor -5.5V Generated by the Charge Pump Transmitter Output 8, 10 8 RIN_ 11, 13 9 ROUT_ Receiver Input Receiver Output 12, 14 10 TIN_ Transmitter Input 15 11 TXENABLE Transmitter Enable. Drive TXENABLE high to enable transmitter. Drive TXENABLE low to put transmitter into high impedance. 16 12 RENABLE Receiver Termination Enable. Drive RENABLE high for normal RS-232 5kΩ termination. Drive RENABLE low to make receiver inputs high impedance. In either case, the receiver and its output are enabled. 17 13 VL 18 14 SHDN 19 15 GND Ground 20 16 VCC +3V to +5.5V Input Voltage. Bypass VCC to GND with a 0.1µF capacitor. Logic-Level Supply. All CMOS inputs and outputs are referred to VL, which is from 1.65V to 5.5V. Shutdown Input. Drive SHDN low to put device into shutdown mode. Drive SHDN high for normal operation. In shutdown, all transmitter and receiver outputs are in three-state; receiver inputs are high impedance. Detailed Description The MAX3322E/MAX3323E are RS-232 transceivers for multidrop applications (i.e., multiple-receiver operation). The devices are pin selectable between standard RS-232 operation with 5kΩ input resistance receivers or highinput-impedance receivers. Receivers of the MAX3322E/ MAX3323E remain active in both modes of operation. In multidrop applications, a selected receiver is set at a 5kΩ input resistance, while the others are high-input impedance, maintaining RS-232 standards. Logic control permits selection of the functional mode: high impedance or normal load. The transmitters are enabled by logic control to allow transmission-line sharing. The logic supply input (VL) controls the levels of the system’s I/O and works from 1.65V to 5.5V, providing compatibility with lower microprocessor I/O voltages. The transmitters are inverting level translators that convert CMOS logic levels into RS-232-compatible levels. They guarantee 250kbps with loads of RL = 3kΩ and CL = 1000pF. The transmitters are enabled or disabled (three-stated) by the logic control TXENABLE, which manages transmission-line sharing in multidrop applications. When TXENABLE is high, the transmitter is enabled. When TXENABLE is low, the transmitter is put in high-impedance state. The receivers can be used in two conditions, selectable by the logic control RENABLE. When RENABLE is high, the internal 5kΩ resistor is connected across receiver input and ground. When RENABLE is low, the receiver input is high impedance, while maintaining receiving capability. In shutdown mode, all transmitter and receiver outputs are three-stated, receiver inputs are in high impedance, the charge pump is turned off, V+ decays to VCC, and V- decays to ground. ESD protection structures are incorporated in all pins to protect against ESD events encountered during handling and assembly. The receiver inputs and the transmitter outputs have ±15kV ESD structure implementation. _______________________________________________________________________________________ 5 MAX3322E/MAX3323E Pin Description MAX3322E/MAX3323E ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications +3V +3V 0V INPUT 50% 50% 50% INPUT 0V V+ 0V V- OUTPUT tPLH tPHL Figure 1. Transmitter Propagation-Delay Timing POWERMANAGEMENT UNIT OR KEYBOARD CONTROLLER 50% OUTPUT VCC GND tPLH tPHL Figure 2. Receiver Propagation-Delay Timing ing capacitor (C1, C2) and reservoir capacitor (C3, C4) to generate the V+ and V- supplies. Because supply voltages can vary from +3V up to +5.5V, the selection of the capacitor values depends on the V CC value. Table 2 shows minimum capacitor values. SHDN RS-232 Transmitters I/O CHIP POWER SUPPLY VL VL The transmitters are inverting level translators that convert CMOS-logic levels to 5.0V EIA/TIA-232 levels. The transmitters are enabled or disabled (three-stated) by the logic control TXENABLE, which manages transmission-line sharing in multidrop applications. When TXENABLE is high, the transmitter is enabled. When TXENABLE is low, the transmitter is put in a highimpedance state (see Table 1). SHDN MAX3322E I/O CHIP WITH UART RS-232 CPU The MAX3322E/MAX3323Es’ 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 3 shows a complete system connection. RS-232 Receivers Figure 3. Interface Under Control of PMU Dual Charge-Pump Voltage Converter The MAX3322E/MAX3323Es’ 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 fly- MAX3322E/MAX3323E receivers convert RS-232 signals to CMOS-logic output levels. The unique feature of the receivers is the switchable input resistance. The receiver input resistance can be 5kΩ or high impedance. These two conditions are selectable by the logic control RENABLE. When RENABLE is high, the 5kΩ resistor is connected across the receiver input and ground. When RENABLE is low, the receiver input is high impedance, maintaining receiving capability. This feature permits the design of multidrop applications, which observe RS-232 interface standards. LapLink is a trademark of Traveling Software. 6 _______________________________________________________________________________________ ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications TXENABLE RENABLE SHDN TRANSMITTER OUTPUT RECEIVER OUTPUT RECEIVER INPUT 1 1 0 High-Z High-Z High-Z 1 1 1 Active Enabled 5kΩ 1 0 0 High-Z High-Z High-Z 1 0 1 Active Enabled High-Z 0 1 0 High-Z High-Z High-Z 0 1 1 High-Z Enabled 5kΩ 0 0 0 High-Z High-Z High-Z 0 0 1 High-Z Enabled High-Z 5V/div T2 2V/div T1 VCC = 3.3V C1–C4 = 0.1µF 50µs/div Figure 4. Transmitter Outputs when Exiting Shutdown High-input impedance is guaranteed from -13.0V to +13.0V, when the receiver is in high-input-impedance mode. The receiver is able to withstand the RS-232 maximum input voltage of ±25V. Shutdown Mode Supply current falls to less than 10µA when the MAX3322E/MAX3323E are placed in shutdown mode (logic low). When in shutdown mode, the devices’ charge pumps are turned off, V+ decays to VCC, V- is pulled to ground, the transmitter outputs and the receiver outputs are disabled (high impedance), and the receiver inputs are in high impedance (Table 1). The device enters shutdown when VL or VCC is absent. The time required to exit shutdown is typically 50µs, as shown in Figure 4. Connect SHDN to VCC if shutdown mode is not used. VL Logic Supply Input Unlike other RS-232 interface devices, in which the receiver outputs swing between 0 and V CC , the MAX3322E/MAX3323E feature a separate logic supply input (VL) that sets VOUT for the receiver outputs and sets thresholds for the transmit and shutdown inputs. This feature allows a great deal of flexibility in interfacing to many types of systems with different logic levels. Connect this input to the host logic supply (1.65V ≤ VL ≤ 5.5V). ±15kV ESD Protection To protect the MAX3322E/MAX3323E against ESD, transmitters and receivers have extra protection against static electricity to protect the device up to ±15kV. The ESD structures withstand high ESD in all states: normal operation, shutdown, and powered down. ESD protection can be tested in various ways; the transmitter and receiver pins are characterized for protection to the following limits: • ±15kV using the Human Body Model • ±8kV using the IEC 1000-4-2 Contact Discharge method • ±15kV using the IEC 1000-4-2 Air-Gap method Note: ESD performance depends on many conditions. Contact Maxim for a reliability report that documents test setup, test methodology, and test results. Human Body Model Figure 5 shows the Human Body Model, and Figure 6 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. _______________________________________________________________________________________ 7 MAX3322E/MAX3323E Table 1. Tx/Rx Logic RC 1MΩ CHARGE-CURRENTLIMIT RESISTOR RD 1.5kΩ 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 5. Human Body ESD Test Model IEC 1000-4-2 The IEC 1000-4-2 standard covers ESD testing and performance of finished equipment; it does not refer specifically to integrated circuits. The MAX3322E/ MAX3323E help the user design equipment that meets level 4 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 a 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 7 shows the IEC 1000-4-2 model. Figure 8 shows the current waveform it generates when discharged into a low impedance. The Air-Gap Discharge 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. Therefore, after PC board assembly, the Machine Model is less relevant to I/O ports. TIME tRL tDL CURRENT WAVEFORM Figure 6. Human Body Model Current Waveform RC 50Ω to 100Ω RD 330Ω CHARGE-CURRENTLIMIT RESISTOR HIGHVOLTAGE DC SOURCE Cs 150pF DISCHARGE RESISTANCE STORAGE CAPACITOR DEVICE UNDER TEST Figure 7. IEC 1000-4-2 ESD Test Model I 100% 90% I PEAK MAX3322E/MAX3323E ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications Applications Information 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 capacitors 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 8 ____________________________________________________ 10% t r = 0.7ns TO 1ns t 30ns 60ns Figure 8. IEC 1000-4-2 ESD Generator Current Waveform ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications 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-. 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 Multidrop Applications The MAX3323E connects to the RS-232 serial port of computer peripherals such as a bar-code scanner, video security controls, industrial multimeters, etc., and allows multiple devices to share the same communication cable connected to a PC. Figure 9 shows a PC UART transmitting to a single receiver with a 5kΩ termination resistor while the other receivers remain in a high-impedance state. When the receiver inputs are high impedance, they remain active and maintain receiving capability. This feature permits the design of multidrop applications, which observe the RS-232 interface standard. Transmitters are enabled and disabled through TXENABLE, allowing the sharing of a single bus line. Transmitters are high impedance when disabled. The host PC’s transmitter stays enabled at all times. Only one peripheral transmitter remains enabled at any time. If the host PC wants to communicate with another peripheral, it first must tell the current peripheral to deassert its transmitter. PC UART MAX3323E MAX3323E 5kΩ 5kΩ PERIPHERAL CONTROL WITH UART MAX3323E 5kΩ PERIPHERAL CONTROL WITH UART PERIPHERAL CONTROL WITH UART Figure 9. Multidrop Application _______________________________________________________________________________________ 9 MAX3322E/MAX3323E on the transmitter outputs and slightly reduces power consumption. The values of 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 C2, C3, and C4 to maintain the proper ratios (C1 to the other capacitors). MAX3322E/MAX3323E ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications MAX3322E fig11 +3.3V T1IN 5V/div 0.1µF SHDN C1 0.1µF 3 C14 C2 0.1µF VCC 1 C1+ V+ 2 C3 0.1µF MAX3323E C2+ V- 5 C2- T1OUT 5V/div 6 C4 0.1µF R1OUT 5V/div VCC = 3.3V T_OUT T_IN 2µs/div 1000pF R_IN R_OUT Figure 11. Loopback Test Results at 125kbps 5kΩ MAX3322E fig12 T1IN 5V/div GND T1OUT 5V/div Figure 10. Loopback Test Circuit Power-Supply Decoupling In most circumstances, a 0.1µF bypass capacitor is adequate. In applications 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. R1OUT 5V/div VCC = 3.3V 1µs/div Figure 12. Loopback Test Results at 250kbps High Data Rates The MAX3322E/MAX3323E maintain the RS-232 ±5.0V minimum transmitter output voltage even at high data rates. Figure 10 shows a transmitter loopback test circuit. Figure 11 shows a loopback test result at 125kbps, and Figure 12 shows the same test at 250kbps. For Figure 11, all transmitters were driven simultaneously at 125kbps into RS-232 loads in parallel with 1000pF. For Figure 12, a single transmitter was driven at 250kbps, and all transmitters were loaded with an RS-232 receiver in parallel with 1000pF. 10 Interconnection with 3V and 5V Logic The MAX3322E/MAX3323E 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. ______________________________________________________________________________________ ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications TOP VIEW +3.3V 18 SHDN C1 0.1µF 4 C2 0.1µF 20 17 VCC 1 C1+ 3 C1- TXENABLE RENABLE VL V+ MAX3322E C2+ V- T1OUT C4 0.1µF 7 V+ 2 15 GND 14 SHDN MAX3323E 13 VL C2- 5 12 RENABLE V- 6 11 TXENABLE 10 TIN1 TOUT1 7 9 RIN1 8 9 T2OUT 14 T2IN 16 VCC C2+ 4 6 5 C2- C1+ 1 C1- 3 2 C3 0.1µF 12 T1IN TTL/CMOS INPUTS Pin Configurations (continued) RS-232 OUTPUTS ROUT1 TSSOP/DIP 15 ENABLE CONTROL 16 Functional Diagram VL 11 R1OUT R1IN 10 C1+ C1- C2+ C2- TTL/CMOS OUTPUTS 5kΩ RS-232 INPUTS VL R2IN 8 13 R2OUT MAX3322E MAX3323E VCC V+ CHARGE PUMP V- VL 5kΩ HIGH IMPEDANCE ROUT RIN GND 5kΩ 19 RENABLE VL V+ Chip Information TRANSISTOR COUNT: 1294 PROCESS: BiCMOS TOUT TIN VSHDN TXENABLE ______________________________________________________________________________________ 11 MAX3322E/MAX3323E Typical Operating Circuit MAX3322E/MAX3323E ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) 12 ______________________________________________________________________________________ ±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX3322E/MAX3323E Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)