19-2443; Rev 3; 9/11 ±50V Isolated, 3.0V to 5.5V, 250kbps, 2 Tx/2 Rx, RS-232 Transceiver The MAX3250 is a 3.0V to 5.5V powered, ±50V isolated EIA/TIA-232 and V.28/V.24 communications interface with high data-rate capabilities. The MAX3250 is a dual die part that operates with up to ±50V difference between the RS-232 side and the logic side (ISOCOM to GND). This makes the device ideal for operation in noisy conditions with high common-mode voltages. This feature prevents damage to the device if RS-232 lines are inadvertently short-circuited to a +24V or ±48V power bus. The MAX3250 is powered by a single 3V to 5.5V supply on the logic side. Power is transferred from the logic side to the isolated side by ±100V external capacitors. The MAX3250 has two receivers (Rx) and two drivers (Tx) and is guaranteed to run at data rates of 250kbps while maintaining RS-232 output levels. The transceivers have a proprietary low-dropout transmitter output stage, delivering true RS-232 performance from a 3V to 5.5V supply with a dual charge pump. The device features a FAULT open-drain output to signal an excessive isolated-side voltage condition on any of the RS232 inputs. This output can drive an alarm LED or can be monitored by the processor to prevent operation under these conditions. The receiver outputs are high impedance in shutdown, allowing multiple interfaces (IrDA, RS-232, RS-485) to be connected to the same UART. The MAX3250 is available in a space-saving 28-pin SSOP package. Applications Features o ±50V Isolation o 20µA Supply Current in Shutdown o 250kbps Guaranteed Data Rate o FAULT Output o High-Impedance Transmitter and Receiver Outputs in Shutdown o Space-Saving SSOP Package o Inductorless/Transformerless Design Simplifies EMI Compliance o Low-Cost Replacement for Opto-Isolated Transceivers o Meets EIA/TIA-232 Specifications Down to 3.0V Ordering Information PART TEMP RANGE MAX3250CAI+ 0°C to +70°C PIN-PACKAGE 28 SSOP MAX3250EAI+ -40°C to +85°C 28 SSOP +Denotes a lead(Pb)-free/RoHS-compliant package. Pin Configuration TOP VIEW + C1- 1 28 VCC Industrial Control R1OUT 2 27 C2- Programmable Logic Controller R2OUT 3 26 GND Point-of-Sale Equipment T1IN 4 PC-to-Router Connections T2IN 5 Diagnostic Ports N.C. 6 Telecom Equipment N.C. 7 22 N.C. C1+ 8 21 C2+ C3+ 9 20 ISOVCC Typical Operating Circuit appears at end of data sheet. 25 FAULT 24 SHDN MAX3250 23 N.C. V+ 10 19 R1IN C3- 11 18 R2IN C4+ 12 17 T1OUT C4- 13 16 T2OUT V- 14 15 ISOCOM SSOP ________________________________________________________________ Maxim Integrated Products For pricing delivery, and ordering information please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX3250 General Description MAX3250 ±50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver ABSOLUTE MAXIMUM RATINGS C1+, C2+, C3+, C3-, C4+, C4(All voltages referenced to GND, unless otherwise noted.) to ISOCOM .....................................-0.3V to (ISOVCC + 0.3V) VCC ...........................................................................-0.3V to +6V ISOCOM...............................................................................±80V T_OUT Current ..............30mA (continuous), 50mA (peak, 10µs) ISOVCC to ISOCOM.................................................-0.3V to +6V R_IN Current..................30mA (continuous), 50mA (peak, 10µs) V+ to ISOCOM (Note 1)............................................-0.3V to +7V ISOCOM Current ...........30mA (continuous), 50mA (peak, 10µs) V- to ISOCOM (Note 1)............................................+0.3V to -7V Short-Circuit Duration T_OUT to ISOCOM .................Continuous V+ + |V-| (Note 1) ...................................................................13V Continuous Power Dissipation (TA = +70°C) 28-Pin SSOP (derate 15mW/°C above +70°C) .......1201.2mW Input Voltages Operating Temperature Ranges T_IN, SHDN ...........................................................-0.3V to +6V MAX3250CAI .....................................................0°C to +70°C R_IN to ISOCOM...............................................................±25V MAX3250EAI...................................................-40°C to +85°C Output Voltages Storage Temperature Range .............................-65°C to +150°C T_OUT to ISOCOM ........................................................±13.2V Lead Temperature (soldering, 10s) .................................+300°C R_OUT .....................................................-0.3V to (VCC + 0.3V) FAULT....................................................................-0.3V to +6V Soldering Temperature (reflow) .......................................+260°C C1-, C2- ......................................................-0.3V to (VCC + 0.3V) Note 1: V+ and V- can have a maximum magnitude 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. ELECTRICAL CHARACTERISTICS (VCC = 3.0V to 5.5V, see Typical Operating Circuit and Table 1 for capacitor values, ISOCOM = GND, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 3.3V and TA = +25°C.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS SHDN = VCC, no load 15 35 mA SHDN = GND, VISOCOM = GND 20 DC CHARACTERISTICS Supply Current Supply Current Shutdown SHDN = GND, VISOCOM = ±50V Maximum Ground Differential |VGND - VISOCOM| Isolation Resistance Between GND and ISOCOM 45 ±350 50 60 µA V kΩ LOGIC INPUTS Input Logic Low T_IN, SHDN Input Logic High T_IN, SHDN 0.8 VCC = 3.3V 2.0 VCC = 5.0V 2.4 Transmitter Input Hysteresis V V 0.5 V T_IN, SHDN -1 ±0.01 +1 µA Output Leakage Current SHDN = GND -10 ±0.05 +10 µA Output-Voltage Low IOUT = 1.6mA 0.4 V Output-Voltage High IOUT = -1.0mA FAULT OUTPUT Output-Voltage Low (Open Drain) Output Leakage Current IOUT = 5mA FAULT Trip Level |VGND - VISOCOM| Input Leakage Current RECEIVER OUTPUTS 2 VCC - 0.6 VCC - 0.1 FAULT not asserted 55 _______________________________________________________________________________________ V 0.4 V 1 µA V ±50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver (VCC = 3.0V to 5.5V, see Typical Operating Circuit and Table 1 for capacitor values, ISOCOM = GND, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 3.3V and TA = +25°C.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS +25 V RECEIVER INPUTS (relative to ISOCOM) Input-Voltage Range -25 Input Threshold Low TA = +25°C Input Threshold High TA = +25°C VCC = 3.3V 1.2 0.6 VCC = 5.0V 1.3 0.8 VCC = 3.3V 2.4 1.6 VCC = 5.0V 2.4 1.7 Input Hysteresis V 0.5 Input Resistance TA = +25°C 3 5 V V 7 kΩ TRANSMITTER OUTPUTS (relative to ISOCOM) Output-Voltage Swing All transmitter outputs loaded with 3kΩ to ISOCOM, TA = +25°C ±5.0 ±5.4 V Output Resistance ISOVCC = V+ = V- = 0V, VT_OUT = ±2V 300 10M Ω -60 +60 mA VCC = 0 or 3V to 5.5V, VT_OUT = ±12V, SHDN = GND -25 +25 µA Output Short-Circuit Current Output Leakage Current TIMING CHARACTERISTICS (VCC = 3.0V to 5.5V, see Typical Operating Circuit and Table 1 for capacitor values, ISOCOM = GND, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 3.3V and TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS Maximum Data Rate RL = 3kΩ, CL = 1000pF to ISOCOM, one transmitter, TA = +25°C Receiver Propagation Delay R_IN to R_OUT, CL = 150pF to GND 0.4 Receiver Skew |tPHL - tPLH| 100 ns Transmitter Skew |tPHL - tPLH| (Note 3) 120 ns Transition-Region Slew Rate VCC = 3.3V, TA = +25°C, RL = 3kΩ to 7kΩ to ISOCOM, measured from +3V to -3V or -3V to +3V 250 kbps µs CL = 150pF to 1000pF to ISOCOM 6 30 CL = 150pF to 2500pF to ISOCOM 4 30 V/µs FAULT Propagation Delay 0.3 µs Time to Shutdown 0.5 µs Time to Exit Shutdown VISOCOM = GND 300 VISOCOM = ±50V 350 µs Note 2: All currents into the device are positive; all currents out of the device are negative. All voltages are referenced to device ground, unless otherwise noted. Note 3: Transmitter skew is measured at the transmitter zero crosspoints. _______________________________________________________________________________________ 3 MAX3250 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VCC = 3.3V, 250kbps data rate, see Typical Operating Circuit and Table 1 for capacitor values, all transmitters loaded with 3kΩ and CL to ISOCOM, TA = +25°C, unless otherwise noted.) SLEW RATE vs. LOAD CAPACITANCE 2 0 -2 20 -SLEW 15 +SLEW 10 T1 TRANSMITTING AT 250kbps T2 TRANSMITTING AT 20kbps 80 SUPPLY CURRENT (mA) T1 TRANSMITTING AT 250kbps T2 TRANSMITTING AT 20kbps 90 MAX3250 toc02 VOUT+ 25 SLEW RATE (V/µs) 6 4 30 MAX3250 toc01 8 OPERATING SUPPLY CURRENT vs. LOAD CAPACITANCE 70 60 250kbps 50 40 120kbps 30 20 20kbps 5 VOUT- 10 FOR DATA RATES UP TO 250kbps -6 0 0 1000 2000 3000 4000 5000 0 0 1000 LOAD CAPACITANCE (pF) 2000 3000 4000 5000 0 1000 LOAD CAPACITANCE (pF) 2000 3000 4000 LOAD CAPACITANCE (pF) SHUTDOWN CURRENT vs. TEMPERATURE TIME TO EXIT SHUTDOWN VISOCOM = 0V MAX3250 toc04 400 SHDN 5V/div ISOCOM = -50V 300 SUPPLY CURRENT (µA) TOUT 5V/div MAX3250 toc05 -4 MAX3250 toc03 TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE TRANSMITTER OUTPUT VOLTAGE (V) 200 100 ISOCOM = 0V 0 -100 -200 ISOCOM = +50V -300 100µs/div -40 -15 10 35 60 85 TEMPERATURE (°C) PEAK GROUND OFFSET VOLTAGE vs. FREQUENCY COMMON-MODE FAULT RESPONSE MAX3250 toc07 MAX3250 toc06 60 VCC = 5V 50 PEAK GROUND OFFSET (±V) MAX3250 ±50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver ISOCOM 50V/div 40 30 VCC = 3.3V 20 FAULT 5V/div 10 0 0 100 200 300 400 500 600 4ms/div FREQUENCY (Hz) 4 _______________________________________________________________________________________ 5000 ±50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver PIN NAME FUNCTION Negative Terminal of the Power Isolation Capacitor. Connect a 100V capacitor from C1- to C1+. See Table 1 for values. 1 C1- 2 R1OUT 3 R2OUT TTL/CMOS Receiver Output 4 T1IN TTL/CMOS Transmitter Input TTL/CMOS Receiver Output 5 T2IN TTL/CMOS Transmitter Input 6, 22, 23 N.C. No Connection. Not internally connected. 7 N.C. No Connection. Leave unconnected or connect to ISOCOM. 8 C1+ Positive Terminal of the Power Isolation Capacitor. Connect a 100V capacitor from C1+ to C1-. See Table 1 for values. 9 C3+ Positive Terminal of the Voltage-Doubler Charge-Pump Capacitor. Connect a 0.1µF capacitor from C3+ to C3-. 10 V+ +5.5V Generated by the Charge Pump, Referenced to ISOCOM. Bypass V+ to ISOCOM with a 0.47µF capacitor. 11 C3- Negative Terminal of the Voltage-Doubler Charge-Pump Capacitor. Connect a 0.1µF capacitor from C3- to C3+. 12 C4+ Positive Terminal of the Inverting Charge-Pump Capacitor. Connect a 0.47µF capacitor from C4+ to C4-. 13 C4- Negative Terminal of the Inverting Charge-Pump Capacitor. Connect a 0.47µF capacitor from C4- to C4+. 14 V- 15 ISOCOM 16 T2OUT RS-232 Transmitter Output 17 T1OUT RS-232 Transmitter Output 18 R2IN RS-232 Receiver Input 19 R1IN RS-232 Receiver Input 20 ISOVCC 21 C2+ 24 SHDN Shutdown Control. Drive SHDN low to enter low-power shutdown mode. Drive SHDN high or connect to VCC for normal operation. 25 FAULT Overvoltage Indicator. Active low, open drain. 26 GND Ground 27 C2- Negative Terminal of the Power Isolation Capacitor. Connect a 100V capacitor from C2- to C2+. See Table 1 for values. 28 VCC 3.0V to 5.5V Supply Voltage. Bypass VCC to GND with a 1µF capacitor. -5.5V Generated by the Charge Pump, Referenced to ISOCOM. Bypass V- to ISOCOM with a 0.47µF capacitor. Isolated Ground Internally Generated Isolated Power-Supply Voltage, Referenced to ISOCOM. Bypass ISOVCC to ISOCOM with a 2.2µF capacitor. Positive Terminal of the Power Isolation Capacitor. Connect a 100V capacitor from C2+ to C2-. See Table 1 for values. _______________________________________________________________________________________ 5 MAX3250 Pin Description MAX3250 ±50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver TIN1 TOUT1 RIN1 ROUT1 TIN2 TOUT2 ROUT2 RIN2 SHDN ISOVCC FAULT OSC V+ MAX3250 RS-232 CHARGE PUMP VCC POWER CONTROLLER FAULT DETECTOR GND C1- C2- C1+ C2+ C3+ C3C4+ C4V- ISOCOM Figure 1. Functional Diagram Detailed Description The MAX3250 is a 3.0V to 5.5V powered, ±50V isolated EIA/TIA-232 and V.28/V.24 communications interface with high data-rate capabilities. The MAX3250 is a dual die part that operates with up to ±50V difference between the RS-232 side and the logic side (ISOCOM to GND). This makes the device ideal for operation in noisy conditions with high common-mode voltages. This feature prevents damage to the device if RS-232 lines are inadvertently short-circuited to a +24V or ±48V power bus. The MAX3250 typically draws 15mA of supply current when unloaded. Supply current drops to 20µA when the device is placed in shutdown mode. 6 The MAX3250 has two receivers and two drivers and is guaranteed to operate at data rates up to 250kbps. The device features a FAULT open-drain output to signal an excessive isolated-side voltage condition on any of the RS-232 inputs. This output can drive an alarm LED or can be monitored by the processor to prevent operation under these conditions. The receiver outputs are high impedance in shutdown, allowing multiple interfaces (IrDA, RS-232, RS-485) to be connected to the same UART (Figure 1). The MAX3250 is a low-cost replacement for opto-isolated transceivers. Isolated Power Supply The MAX3250 drives a high-frequency square wave into C1 and a complementary square wave into C2. These _______________________________________________________________________________________ ±50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver Dual Charge-Pump Voltage Converter The RS-232 drivers are powered from a regulated dual charge pump that provides output voltages of +5.5V (doubling charge pump) and -5.5V (inverting charge pump) relative to ISOCOM over the 3.0V to 5.5V VCC range. The charge pumps are powered from ISOVCC and 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 (C3, C4) and a reservoir capacitor (C7, C8) to generate the V+ and V- supplies. RS-232 Transmitters The transmitters are inverting level translators that convert TTL/CMOS-logic levels to ±5.0V EIA/TIA-232-compliant levels. They guarantee a 250kbps data rate with worstcase loads of 3kΩ in parallel with 1000pF to ISOCOM. In shutdown, the transmitters are disabled and the outputs are forced into a high-impedance state. When powered off or shut down, the outputs can be driven up to ±12V relative to ISOCOM. The transmitter inputs do not have pullup resistors. All unused inputs should be connected to VCC or GND. RS-232 Receivers The receivers convert RS-232 signals to CMOS-logic output levels. The receivers’ outputs are forced into a high-impedance state when the device is in shutdown. This allows a single UART to multiplex between different protocols. Low-Power Shutdown Mode Shutdown mode is obtained by driving SHDN low. In shutdown, the devices typically draw only 20µA of supply current and no power is transferred across the isolation capacitors. The charge pumps are disabled, and the receiver outputs and transmitter outputs are high impedance. When exiting shutdown the charge pumps and transmitter outputs are fully operational in typically 500µs (Figure 3). Connect SHDN to VCC if the shutdown mode is not used. Applications Information Power Isolation Capacitors The values for capacitors C1 and C2 are important for proper operation of the device. These capacitors should be 0.047µF for 4.5V to 5.5V operation, and 0.47µF for 3.0V to 3.6V operation. Smaller values result in insufficient supply voltage on the isolated side. Larger values are not allowed. Capacitor C9 provides an AC feedback path for proper controller operation. Connect C9 from ISOCOM to GND. The values for C1, C2, and C9 determine the maximum frequency and amplitude of the voltage difference between the local and isolated ground. Table 1 shows proper capacitance values. TRANSMITTER OUTPUT VOLTAGE (V) 6 5 VCC = 3.0V SHDN 5V/div VOUT+ 4 3 T1OUT 2 1 0 -1 VCC T1 VOUT1+ T2 VOUT2- 2V/div -2 -3 -4 -5 -6 VOUTVCC = 3.3V 0 1 2 3 4 5 6 7 8 T2OUT 100µs/div LOAD CURRENT PER TRANSMITTER (mA) Figure 2. Transmitter Output Voltage vs. Load Current per Transmitter Figure 3. Transmitter Outputs when Exiting Shutdown or Powering Up _______________________________________________________________________________________ 7 MAX3250 AC waveforms are rectified on the isolated side of the dual die to power its internal circuitry (ISOVCC). Capacitor C6 filters the output of the rectifier. See the Typical Operating Circuit. The power controller works in a dual power mode. Power is maximum when the isolated power supply is below its regulation point. Power is reduced when the isolated power supply is above its regulation point. MAX3250 ±50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver Table 1. Required Capacitor Values C1, C2 (µF) C3 (µF) C4, C7, C8 (µF) C5 (µF) C6 (µF) C9 (nF) 3.0 to 3.6 0.47 0.1 0.47 1 2.2 10 4.5 to 5.5 0.047 0.1 0.47 1 2.2 10 VCC (V) To achieve full isolation capability, C1, C2, and C9 should be rated for 100V or higher operation and be X7R or X5R type or metalized film dielectric. Y5V and Z5U dielectrics should be avoided as their voltage and temperature coefficients make their power-transfer capabilities insufficient. Charge-Pump and Bypass Capacitors Capacitors C3–C8 should be X7R or X5R type dielectric. Their voltage rating needs to be 10V or higher. Layout Information Because the MAX3250 is intended for systems requiring ±50V isolation, some consideration in component placement is necessary. A 20mil air gap should isolate the logic side and the isolated RS-232 side, across the N.C. pins (pin numbers 6, 7, 22, and 23) of the MAX3250. The only components that cross this air gap should be C1, C2, and C9, which should all have a minimum 100V rating. All capacitors should be located as close to the MAX3250 as possible. 8 Maximum Voltage Between ISOCOM and Logic GND High values of applied isolation voltage and frequency can cause ripple on ISOVCC, V+, V-, and in extreme cases on VCC. Therefore, it is recommended that the isolation-voltage and frequency be limited to the values shown in the Typical Operating Characteristics. Insert a 1kΩ 1/4W resistor in series with any isolation test voltage when testing for maximum values of applied isolation voltage. Exceeding the maximum limits of voltage and frequency (see the Typical Operating Characteristics) could trigger a holding current in the internal ESD-protection device if the ±80V isolation limit is exceeded. This resistor should not be used in normal application. Transmitter Outputs when Exiting Shutdown Figure 3 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. _______________________________________________________________________________________ ±50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver REMOTE XCVR VCC C5 1µF CABLE VCC REMOTE MICRO RIN1 TOUT1 FAULT RIN2 MICRO SHDN TIN1 ROUT1 TIN2 ROUT2 C1 0.47µF C2 0.47µF TOUT2 C4+ MAX3250 C4 0.47µF C4C3+ C3 0.1µF C3V+ C1+ C1C2+ VISOVCC C6 2.2µF C2GND C8 0.47µF C7 0.47µF ISOCOM C9 10nF ±50V GND OFFSET Package Information Chip Information PROCESS: BiCMOS REMOTE GROUND For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 28 SSOP A28M+3 21-0056 90-0095 _______________________________________________________________________________________ 9 MAX3250 Typical Operating Circuit MAX3250 ±50V Isolated, 3.0V to 5.5V, 250kbps, 2 TX/2 RX, RS-232 Transceiver Revision History REVISION NUMBER REVISION DATE 0 4/02 Initial release — 1 2/03 Updated Design — 2 1/08 Updated EC table 3 3 9/11 Added lead-free packaging information; corrected pin names, power dissipation, and soldering temperature in Absolute Maximum Ratings; updated capacitor values in data sheet. DESCRIPTION PAGES CHANGED 1, 2, 3, 5–9 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. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. 10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.