19-4098; Rev 0; 5/08 ±80V Fault-Protected Full-Duplex RS-485 Transceiver Features The MAX13448E full-duplex RS-485 transceiver features inputs and outputs fault protected up to ±80V (with respect to ground). The device operates from a +3.0V to +5.5V supply and features true fail-safe circuitry, guaranteeing a logic-high receiver output when the receiver inputs are open or shorted. This enables all receiver outputs on a terminated bus to output logichigh when all transmitters are disabled. The MAX13448E features a slew-rate limited driver that minimizes EMI and reduces reflections caused by improperly terminated cables, allowing error-free data transmission at data rates up to 500kbps with a +5V supply, and 250kbps with a +3.3V supply. o ±80V Fault Protection on the RS-485 I/O Ports The MAX13448E includes a hot-swap capability to eliminate false transitions on the bus during power-up or hot insertion. The driver and receiver feature active-high and active-low enables, respectively, that can be connected together externally to serve as a direction control. o +3.0V to +5.5V Operating Supply Voltage o True Fail-Safe Receiver o Hot-Swap Input Structure on DE o ESD Protection on the RS-485 I/O Ports ±8kV Human Body Model o Slew-Rate Limiting Facilitates Error-Free Data Transmission o 1/8-Unit Load Allows Up to 256 Transceivers on the Bus o -7V to +12V Common-Mode Input Voltage Range o Available in 14-Pin SO Package The MAX13448E features an 1/8-unit load receiver input impedance, allowing up to 256 transceivers on the bus. All driver outputs are protected to ±8kV ESD using the Human Body Model. The MAX13448E is available in a 14-pin SO package and operates over the extended -40°C to +85°C temperature range. Ordering Information PART TEMP RANGE PIN-PACKAGE MAX13448EESD+ -40°C to +85°C 14 SO +Denotes a lead-free package. Applications Industrial Control Systems HVAC Control systems Pin Configuration appears at end of data sheet. Utility Meters Motor Driver Control Systems Functional Diagram N.C. 1 + 14 VCC MAX13448E DE VCC RO 2 R RE 3 13 N.C. 12 A 9 DI 5 D VCC 1μF 4 14 RE Y Rt 10 RO R Z DE 4 11 B DI 5 10 Z 12 RO D GND 6 9 Y GND 7 8 N.C. N.C. 2 R A Rt 11 1, 8, 13 D DI B 3 RE 6, 7 GND GND DE SO ________________________________________________________________ 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 MAX13448E General Description MAX13448E ±80V Fault-Protected Full-Duplex RS-485 Transceiver ABSOLUTE MAXIMUM RATINGS (All voltages reference to GND.) Supply Voltage (VCC).............................................................+6V Control Input Voltage (RE, DE)...................-0.3V to (VCC + 0.3V) Driver Input Voltage (DI).............................-0.3V to (VCC + 0.3V) Receiver Input Voltage (A, B (Note 1)) ................................±80V Driver Output Voltage (Y, Z (Note 1)) ..................................±80V Receiver Output Voltage (RO)....................-0.3V to (VCC + 0.3V) Short-Circuit Duration (RO, A, B) ...............................Continuous Continuous Power Dissipation (TA = +70°C) 14-Pin SO (derate 8.3mW/°C above +70°C)................667mW Operating Temperature Range ...........................-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: If the RS-485 transmission lines are unterminated and a short to a voltage VSHT occurs at a remote point on the line, an active local driver (with DI switching) may see higher voltage than VSHT due to inductive kickback at the driver. Terminating the line with a resistor equal to its characteristic impedance minimizes this kickback effect. 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 = +3.0 to +5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C.) (Notes 2, 3) PARAMETER VCC Supply Voltage Range Supply Current SYMBOL CONDITION VCC IQ Supply Current in Shutdown Mode ISHDN Supply Current with Output Shorted to ±60V ISHRT MIN TYP 3.0 MAX UNITS 5.5 V No load, DE, DI, RE = 0V or VCC, VCC = 3.3V 15 No load, DE, DI, RE = 0V or VCC, VCC = 5V 15 DE = GND, RE = VCC, VCC = 3.3V 100 DE = GND, RE = VCC, VCC = 5V 100 DE = GND, RE = GND, short to +60V 15 DE = GND, RE = GND, short to -60V 15 mA µA mA DRIVER Differential Driver Output Change in Magnitude of Differential Output Voltage VOD ΔVOD RL = 100Ω, Figure 1 2 VCC RL = 54Ω, Figure 1 1.5 VCC RL = 100Ω or 54Ω, Figure 1 (Note 4) -0.2 0.2 V 3 V +0.2 V Driver Common-Mode Output Voltage VOC RL = 100Ω or 54Ω, Figure 1 Change in Magnitude of Common-Mode Voltage ΔVOC RL = 100Ω or 54Ω, Figure 1 (Note 4) Driver Short-Circuit Output Current IOSD Driver Short-Circuit Foldback Output Current IOSDF Driver-Limit Short-Circuit Foldback Output Current IOSDL Driver Input High Voltage VDIH Driver Input Low Voltage VDIL Driver Input Current IDIN 2 VCC/2 -0.2 DI = low, 0V ≤ VY or VZ ≤ +12V +250 DI = high, -7V ≤ VY or VZ ≤ VCC (Note 5) -250 DI = low, (VCC - 1V) ≤ VY or VZ ≤ +12V +10 DI = high, -7V ≤ VY or VZ ≤ +1V -10 VY or VZ ≥ + 22V, RL = 100Ω VY or VZ ≤ -13V, RL = 100Ω +6 -6 2 -1 _______________________________________________________________________________________ V mA mA mA V 0.8 V +1 µA ±80V Fault-Protected Full-Duplex RS-485 Transceiver (VCC = +3.0 to +5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C.) (Notes 2, 3) PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS +125 µA -6 +6 mA -200 -50 mV RECEIVER VCC = GND or VCC = +3.0V to +5.5V VA, VB = +12V Input Current IA , B VA, VB = -7V -100 VA, VB = ±80V Receiver Differential Threshold Voltage VTH -7V ≤ VCM ≤ +12V Receiver Input Hysteresis ΔVTH Output High Voltage VOH IOH = -1.6mA Output Low Voltage VOL IOL = 1mA Three-State Output Current at Receiver IOZR 0 ≤ VA, VB ≤ VCC Receiver Output Short-Circuit Current IOSR 0 ≤ VRO ≤ VCC µA 25 mV VCC 0.6 V 0.4 V -1 +1 µA -95 +95 mA ESD PROTECTION All Pins Human Body Model ±2 kV ESD Protection Level (A and B, Y and Z) Human Body Model ±8 kV CONTROL Control Input High Voltage VCIH DE, RE Control Input Low Voltage VCIL DE, RE IIN DE, RE Input Current Latch During First Rising Edge 2 V 0.8 80 V µA PROTECTION SPECIFICATIONS Overvoltage Protection A, B, Y, Z -80 +80 V TYP MAX UNITS 700 1500 ns 1200 ns 200 ns SWITCHING CHARACTERISTICS (VCC = +3.3V ±10%) (TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C.) PARAMETER SYMBOL CONDITION MIN DRIVER Driver Differential Propagation Delay tDPLH, tDPHL RL = 54Ω, CL = 50pF, Figures 2 and 3 Driver Differential Output Transition Time tLH, tHL RL = 54Ω, CL = 50pF, Figures 2 and 3 Differential Driver Output Skew tDSKEW RL = 54Ω, CL = 50pF, tDSKEW = [tDPLH tDPHL], Figures 2 and 3 Maximum Data Rate fMAX Driver Enable Time to Output High tDZH 250 150 250 RL = 500Ω, CL = 50pF, Figure 4 kbps 2000 ns _______________________________________________________________________________________ 3 MAX13448E ELECTRICAL CHARACTERISTICS (continued) MAX13448E ±80V Fault-Protected Full-Duplex RS-485 Transceiver SWITCHING CHARACTERISTICS (VCC = +3.3V ±10%) (continued) (TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C.) PARAMETER Driver Disable Time from Output High Driver Enable Time from Shutdown to Output High SYMBOL tDHZ CONDITION MIN TYP RL = 500Ω, CL = 50pF, Figure 4 tDZH(SHDN) RL = 500Ω, CL = 50pF, Figure 4 MAX UNITS 1000 ns 8 µs Driver Enable Time to Output Low tDZL RL = 500Ω, CL = 50pF, Figure 5 1500 ns Driver Disable Time from Output Low tDLZ RL = 500Ω, CL = 50pF, Figure 5 2000 ns 8 µs 12 µs Driver Enable Time from Shutdown to Output Low Driver Time to Shutdown tDZL(SHDN) RL = 500Ω, CL = 50pF, Figure 5 tSHDN RL = 500Ω, CL = 50pF Receiver Propagation Delay tRPLH, tRPHL CL = 20pF, VID = 2V, VCM = 0V, Figure 6 2000 ns Receiver Output Skew tRSKEW CL = 20pF, tRSKEW = [tRPLH - tRPHL], Figure 6 200 ns RECEIVER Receiver Enable Time to Output High tRZH RL = 1kΩ, CL = 20pF, Figure 7 1000 ns Receiver Disable Time from Output High tRHZ RL = 1kΩ, CL = 20pF, Figure 7 150 ns Receiver Wake Time from Shutdown tRWAKE RL = 1kΩ, CL = 20pF, Figure 7 5 µs Receiver Enable Time to Output Low tRZL RL = 1kΩ, CL = 20pF, Figure 7 1000 ns Receiver Disable Time from Output Low tRLZ RL = 1kΩ, CL = 20pF, Figure 7 150 ns Receiver Time to Shutdown tSHDN RL = 500Ω, CL = 50pF 200 ns MAX UNITS 800 ns 1200 ns 200 ns SWITCHING CHARACTERISTICS (VCC = +5V ±10%) (TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.) PARAMETER SYMBOL CONDITION MIN TYP DRIVER Driver Differential Propagation Delay tDPLH, tDPHL RL = 54Ω, CL = 50pF, Figure 3 Driver Differential Output Transition Time tLH, tHL RL = 54Ω, CL = 50pF, Figure 3 Differential Driver Output Skew tDSKEW RL = 54Ω, CL = 50pF, tDSKEW = [tDPLH tDPHL], Figure 3 Maximum Data Rate 4 fMAX 100 500 _______________________________________________________________________________________ kbps ±80V Fault-Protected Full-Duplex RS-485 Transceiver (TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.) PARAMETER SYMBOL MAX UNITS Driver Enable Time to Output High tDZH RL = 500Ω, CL = 50pF, Figure 4 1500 ns Driver Disable Time from Output High tDHZ RL = 500Ω, CL = 50pF, Figure 4 1000 ns 8 µs Driver Enable Time from Shutdown to Output High CONDITION tDZH(SHDN) RL = 500Ω, CL = 50pF, Figure 4 MIN TYP Driver Enable Time to Output Low tDZL RL = 500Ω, CL = 50pF, Figure 5 1000 ns Driver Disable Time from Output Low tDLZ RL = 500Ω, CL = 50pF, Figure 5 2 µs tDZL(SHDN) RL = 500Ω, CL = 50pF, Figure 5 8 µs 12 µs Driver Enable Time from Shutdown to Output Low Driver Time to Shutdown tSHDN RL = 500Ω, CL = 50pF Receiver Propagation Delay tRPLH, tRPHL CL = 20pF, VID = 2V, VCM = 0V, Figure 6 2000 ns Receiver Output Skew tRSKEW CL = 20pF, tRSKEW = [tRPLH - tRPHL], Figure 6 200 ns RECEIVER Receiver Enable Time to Output High tRZH RL = 1kΩ, CL = 20pF, Figure 7 1000 ns Receiver Disable Time from Output High tRHZ RL = 1kΩ, CL = 20pF, Figure 7 150 ns Receiver Wake Time from Shutdown tRWAKE RL = 1kΩ, CL = 20pF, Figure 7 8 µs Receiver Enable Time to Output Low tRZL RL = 1kΩ, CL = 20pF, Figure 7 1000 ns Receiver Disable Time from Output Low tRLZ RL = 1kΩ, CL = 20pF, Figure 7 150 ns Receiver Time to Shutdown tSHDN RL = 500Ω, CL = 50pF 150 ns Note 2: Parameters are 100% production tested at TA = +25°C, unless otherwise noted. Limits over temperature are guaranteed by design. Note 3: 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 4: ΔVOD and ΔVOC are the changes in VOD and VOC, respectively, when the DI input changes state. Note 5: The short-circuit output current applies to peak current just prior to foldback current limiting. The short-circuit foldback output current applies during current limiting to allow a recover from bus contention. _______________________________________________________________________________________ 5 MAX13448E SWITCHING CHARACTERISTICS (VCC = +5V ±10%) (continued) Typical Operating Characteristics (VCC = +3.3V, TA = +25°C, unless otherwise noted.) 3.0 2.8 2.6 +25°C 2.4 2.2 4.05 DE = RE = LOW A - B = HIGH +85°C -15 10 35 TEMPERATURE (°C) 60 85 2 4 6 8 OUTPUT SOURCE CURRENT (mA) 3.22 0 MAX13448E toc03 2 4 6 8 OUTPUT SINK CURRENT (mA) 0.065 0.060 0.055 0.050 0.045 0.040 60 -40 85 2.5 2.0 1.5 DE = RE = HIGH DI = HIGH 1.0 10 35 TEMPERATURE (°C) 60 85 1.94 MAX13448E toc07 3.0 -15 DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE DIFFERENTIAL OUTPUT VOLTAGE (V) MAX13448E toc06 3.5 DIFFERENTIAL OUTPUT VOLTAGE (V) -40°C DE = RE = LOW B - A = HIGH ISINK = 1mA DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. DIFFERENTIAL OUTPUT CURRENT 1.92 1.90 1.88 DE = RE = HIGH DI = HIGH RLOAD = 54Ω 1.86 0 6 0.2 10 0.070 DE = RE = LOW A - B = HIGH ISOURCE = 1mA 10 35 TEMPERATURE (°C) 0.3 0.075 OUTPUT LOW VOLTAGE (V) 3.23 -15 0.4 RECEIVER OUTPUT LOW VOLTAGE vs. TEMPERATURE MAX13448E toc04 OUTPUT HIGH VOLTAGE (V) 3.24 -40 +85°C 0.5 0 0 3.25 3.20 0.6 +25°C RECEIVER OUTPUT HIGH VOLTAGE vs. TEMPERATURE 3.21 0.7 0.1 2.0 -40 DE = RE = LOW B - A = HIGH 0.8 MAX13448E toc05 4.10 -40°C 3.2 0.9 OUTPUT LOW VOLTAGE (V) 4.15 3.4 MAX13448E toc02 DE = RE = LOW A - B = HIGH DI = FLOATING OUTPUT HIGH VOLTAGE (V) MAX13448E toc01 4.20 RECEIVER OUTPUT SINK CURRENT vs. OUTPUT LOW VOLTAGE RECEIVER OUTPUT SOURCE CURRENT vs. OUTPUT HIGH VOLTAGE SUPPLY CURRENT vs. TEMPERATURE SUPPLY CURRENT (mA) MAX13448E ±80V Fault-Protected Full-Duplex RS-485 Transceiver 20 40 60 80 DIFFERENTIAL OUTPUT CURRENT (mA) 100 -40 -15 10 35 TEMPERATURE (°C) 60 _______________________________________________________________________________________ 85 10 ±80V Fault-Protected Full-Duplex RS-485 Transceiver SINGLE-ENDED DRIVER SINK CURRENT vs. OUTPUT LOW VOLTAGE 3.25 3.20 SHUTDOWN CURRENT vs. TEMPERATURE 0.08 0.06 0.04 30 25 2 4 6 8 OUTPUT SOURCE CURRENT (mA) 0 10 15 10 0 0 2 4 6 8 OUTPUT SINK CURRENT (mA) -40 10 -15 10 35 TEMPERATURE (°C) 60 85 RECEIVER PROPAGATION DELAY (500kbsp) DRIVER PROPAGATION DELAY (500kbsp) MAX13448E toc12 MAX13448E toc11 2V/div 1V/div 1V/div 400ns DRIVER PROPAGATION DELAY vs. TEMPERATURE RECEIVER PROPAGATION DELAY vs. TEMPERATURE 400 tDPHL 350 DE = RE = HIGH RLOAD = 54Ω CLOAD = 50pF -40 -15 10 35 TEMPERATURE (°C) MAX13448E toc14 tDPLH 450 400 DE = RE = LOW CLOAD = 20pF PROPAGATION DELAY (ns) 500 300 2V/div 400ns MAX13448E toc13 0 20 5 0.02 3.10 MAX13448E toc10 MAX13448E toc09 DE = RE = HIGH DI = HIGH 0.10 3.15 PROPAGATION DELAY (ns) OUTPUT HIGH VOLTAGE (V) DE = RE = HIGH DI = HIGH 3.30 0.12 OUTPUT LOW VOLTAGE (V) MAX13448E toc08 3.35 SHUTDOWN CURRENT (μA) SINGLE-ENDED DRIVER OUTPUT HIGH VOLTAGE vs. SOURCE CURRENT 375 350 tRPLH 325 tRPHL 300 60 85 -40 -15 10 35 TEMPERATURE (°C) 60 85 _______________________________________________________________________________________ 7 MAX13448E Typical Operating Characteristics (continued) (VCC = +3.3V, TA = +25°C, unless otherwise noted.) ±80V Fault-Protected Full-Duplex RS-485 Transceiver MAX13448E Pin Description PIN NAME FUNCTION 1, 8, 13 N.C. No Connection. Not internally connected. Connect N.C. to GND or leave it unconnected. 2 RO Receiver Output. If receiver is enabled and (A - B) ≥ -50mV, RO = high; if (A - B) ≥ -200mV, RO = low. 3 RE Receiver Output Enable. Drive RE low to enable RO; RO is high impedance when RE is high. Drive RE high and DE low to enter low-power shutdown mode. 4 DE Driver Output Enable. Drive DE high to enable the driver outputs. Drive DE low to put the outputs in high impedance. Drive RE high and DE low to enter low-power shutdown mode. 5 DI Driver Input. Drive DI low to force the noninverting output low and the inverting output high. Drive DI high to force the noninverting output high and the inverting output low. 6, 7 GND Ground 9 Y Noninverting Driver Output 10 Z Inverting Driver Output 11 B Inverting Receiver Input 12 A Noninverting Receiver Input 14 VCC Positive Supply. VCC = +3.0V to +5.5V. Bypass VCC to GND with a 1µF ceramic capacitor as close to VCC as possible. Typical VCC values are at VCC = +3.3V and VCC = +5.0V. Y VCC DI RL/2 VCC/2 0 VOD tDPHL tDPLH Z VO VOC RL/2 Y 1/2 VO Z VO VOD 0 -VO Figure 1. Driver DC Test Load VCC VOD = V (Y) - V (Z) 10% 90% 90% tHL tLH tSKEW = |tDPLH - tDPHL| Figure 3. Driver Propagation Delays DE CL Y DI VO Z RL CL Figure 2. Driver Timing Test Circuit 8 1/2 VO _______________________________________________________________________________________ 10% ±80V Fault-Protected Full-Duplex RS-485 Transceiver D1 S1 D OUT Z GENERATOR MAX13448E Y 0 OR VCC RL = 500Ω CL 50pF 50Ω VCC DE VCC/2 tDZH, tDZH(SHDN) 0 0.25V OUT VOH VOM = (0 + VOH)/2 0 tDHZ Figure 4. Driver Enable and Disable Times (tDHZ, tDZH, tDZH(SHDN)) VCC Y 0 OR VCC D1 D OUT Z GENERATOR RL = 500Ω S1 CL 50pF 50Ω VCC DE VCC/2 tDZL, tDZL(SHDN) 0 tDLZ VCC VOM = (VOL + VCC)/2 OUT VOL 0.25V Figure 5. Driver Enable and Disable Times (tDLZ, tDZL, tDZL(SHDN)) _______________________________________________________________________________________ 9 MAX13448E ±80V Fault-Protected Full-Duplex RS-485 Transceiver B A A RO VID R CL 20pF B tRPHL tRPLH VOH 0 VOH + VOL RO 2 VOL tSKEW = |tRPLH - tRPHL| Figure 6. Receiver Propagation Delays S1 +1.5V S3 A -1.5V VID RO VCC 1kΩ R B RE GENERATOR CL 20pF S2 50Ω S1 OPEN S2 CLOSED S3 = +1.5V S1 CLOSED S2 OPEN S3 = -1.5V VCC VCC VCC/2 RE RE 0 0 tRZH, tRWAKE* tRZL, tSHDN* VOH RO VCC VOH/2 (VOL + VCC)/2 RO 0 S1 OPEN S2 CLOSED S3 = +1.5V VOL S1 CLOSED S2 OPEN S3 = -1.5V VCC VCC/2 VCC/2 RE tRHZ, tSHDN* VCC 0 RE 0 tRLZ, tSHDN* VCC VOH *DE = LOW 0.25V RO 0 RO 0.25V Figure 7. Receiver Enable and Disable Times 10 ______________________________________________________________________________________ VOL ±80V Fault-Protected Full-Duplex RS-485 Transceiver The MAX13448E ±80V fault-protected RS-485/RS-422 transceiver contains one driver and one receiver. This device features fail-safe circuitry, guaranteeing a logichigh receiver output when the receiver inputs are open or shorted, or when they are connected to a terminated transmission line with all drivers disabled. The device has a hot-swap input structure that prevents disturbances on the differential signal lines when a circuit board is plugged into a hot backplane. All receiver inputs and driver outputs are protected to ±8kV ESD using the Human Body Model. The MAX13448E features a reduced slew-rate driver that minimizes EMI and reduces reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps. Driver The driver accepts a single-ended, logic-level input (DI) and converts it to a differential, RS-485/RS-422 level output (A and B). Deasserting the driver enable places the driver outputs (A and B) into a high-impedance state. Receiver The receiver accepts a differential, RS-485/RS-422 level input (A and B), and translates it to a singleended, logic-level output (RO). Deasserting the receiver enable places the receiver outputs (RO) into a high-impedance state (see Table 1). Low-Power Shutdown Low-power shutdown is initiated by bringing DE low and RE high. In shutdown, the device draws a maximum of 100µA of supply current. The device is guaranteed to not enter shutdown if DE is low and RE is high for 1µs. If the inputs are in this state for at least 1ms, the device is guaranteed to enter shutdown. In the shutdown state, the driver outputs (A and B) as well as the receiver output (RO) are in a highimpedance state. ±80V Fault Protection In certain applications, such as industrial control, driver outputs and receiver inputs of an RS-485 device sometimes experience common-mode voltages in excess of the -7V to +12V range specified in the EIA/TIA-485 standard. In these applications, ordinary RS-485 devices (typical absolute maximum ratings of -8V to +12.5V) may experience damage without the addition of external protection devices. Table 1. Function Table TRANSMITTING INPUT OUTPUT RE DE DI Z Y X 1 0 1 0 X 1 1 0 1 0 0 X High Impedance High Impedance 1 0 X High Impedance (Shutdown) RECEIVING INPUT OUTPUT RE DE A-B RO 0 X -50mV 1 0 X -200mV 0 1 1 X Disabled 1 0 X High Impedance (Shutdown) X = Don’t care; shutdown mode, driver, and receiver outputs are high impedance. To reduce system complexity and the need for external protection, the driver outputs and receiver inputs of the MAX13448E withstand voltage faults of up to ±80V with respect to ground without damage (see the Absolute Maximum Ratings section, Note 1). Protection is guaranteed regardless of whether the device is active, in shutdown, or without power. Certain parasitic effects present while driving an unterminated cable may cause the voltage seen at driver outputs to exceed the absolute maximum limit, while the DI input is switched during a ±80V fault on the A or B input. Therefore, a termination resistor is recommend in order to maximize the overvoltage fault protection while the DI input is being switched. If the DI input does not change state while the fault voltage is present, the MAX13448E will withstand up the ±80V on the RS-485 inputs, regardless of the presence of a termination resistor. While the MAX13448E is not damaged by up to ±80V commonmode voltages, the RO, Y, and Z outputs will be in an indeterminate state if the common-mode voltage exceeds -7V to +12V. True Fail-Safe The MAX13448E guarantees a logic-high receiver output when the receiver inputs are shorted or open, or when they are connected to a terminated transmission line with all drivers disabled. This is done by setting the ______________________________________________________________________________________ 11 MAX13448E Detailed Description MAX13448E ±80V Fault-Protected Full-Duplex RS-485 Transceiver RC 1MΩ CHARGE-CURRENTLIMIT RESISTOR HIGHVOLTAGE DC SOURCE Cs 100pF RD 1500Ω IP 100% 90% DISCHARGE RESISTANCE Ir PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE) AMPS STORAGE CAPACITOR DEVICE UNDER TEST 36.8% 10% 0 0 tRL TIME tDL CURRENT WAVEFORM Figure 8a. Human Body ESD Test Model Figure 8b. Human Body Current Waveform receiver threshold between -50mV and -200mV. If the differential receiver input voltage (A - B) is greater than or equal to -50mV, RO is logic-high. If A - B is less than or equal to -200mV, RO is logic-low. In the case of a terminated bus with all transmitters disabled, the receiver’s differential input voltage is pulled to 0V by the termination. With the receiver thresholds of the MAX13448E, this results in a logic-high with a 50mV minimum noise margin. The -50mV to -200mV threshold complies with the ±200mV EIA/TIA-485 standard. 100pF capacitor charged to the ESD voltage of interest, which is then discharged into the test device through a 1.5kΩ resistor. ±8kV ESD Protection As with all Maxim devices, ESD-protection structures are incorporated on all pins to protect against electrostatic discharges encountered during handling and assembly. The driver outputs and receiver inputs of the MAX13448E have extra protection against static electricity. Maxim’s engineers have developed state-of-theart structures to protect these pins against ESD of ±8kV without damage. The ESD structures withstand high ESD in all states: normal operation, shutdown, and powered down. After an ESD event, the MAX13448E keeps working without latchup or damage. ESD protection can be tested in various ways. The transmitter outputs and receiver inputs of the MAX13448E are characterized for protection to the following limits: • ±8kV using the Human Body Model ESD Test Conditions ESD performance depends on a variety of conditions. Contact Maxim for a reliability report that documents test setup, test methodology, and test results. Human Body Model Figure 8a shows the Human Body Model, and Figure 8b shows the current waveform it generates when discharged into a low impedance. This model consists of a 12 Driver Output Protection Two mechanisms prevent excessive output current and power dissipation caused by faults or by bus contention. The first, a foldback current limit on the output stage, provides immediate protection against short circuits over the whole common-mode voltage range (see the Typical Operating Characteristics). The second, a thermal-shutdown circuit, forces the driver outputs into a high-impedance state if the die temperature exceeds +160°C (typ). Hot-Swap Capability Hot-Swap Inputs When circuit boards are inserted into a powered backplane, disturbances to the data bus can lead to data errors. Upon initial circuit-board insertion, the data communication processor undergoes its own power-up sequence. During this period, the processor’s logicoutput drivers are high impedance and are unable to drive the DE input of the device to a defined logic level. Leakage currents up to ±10µA from the high-impedance state of the processor’s logic drivers could cause standard CMOS enable inputs of a transceiver to drift to an incorrect logic level. Additionally, parasitic circuitboard capacitance could cause coupling of VCC or GND to the enable inputs. Without the hot-swap capability, these factors could improperly enable the transceiver’s driver or receiver. When VCC rises, an internal pulldown circuit holds DE low. After the initial power-up sequence, the pulldown circuit becomes transparent, resetting the hot-swap tolerable input. ______________________________________________________________________________________ ±80V Fault-Protected Full-Duplex RS-485 Transceiver VCC 10μs TIMER SR LATCH Proper Termination and Cabling/Wiring Configurations TIMER 5kΩ DE (HOT SWAP) DE 100μA 500μA M1 M2 When the data rates for RS-485 are high relative to its cable lengths, the system is subject to proper transmission line design. In most cases, a single, controlledimpedance cable or trace should be used and should be properly terminated on both ends with the characteristic impedance of the cable/trace. RS-485 transceivers should be connected to the cable/traces with minimum length wires to prevent stubs. Star configurations and improperly terminated cables can cause data loss. Refer to the Applications section of the Maxim website or to TIA/EIA publication TSB89 for further information. Reduced EMI and Reflections Figure 9. Simplified Structure of the Driver Enable Pin (DE) Hot-Swap Input Circuitry The enable inputs feature hot-swap capability. At the input there are two NMOS devices, M1 and M2 (Figure 9). When VCC ramps from zero, an internal 7µs timer turns on M2 and sets the SR latch that also turns on M1. Transistor M2, a 1.5mA current sink, and M1, a 100µA current sink, pull DE to GND through a 5kΩ resistor. M2 is designed to pull DE to the disabled state against an external parasitic capacitance up to 100pF that can drive DE high. After 7µs, the timer deactivates M2 while M1 remains on, holding DE low against three-state leakages that can drive DE high. M1 remains on until an external source overcomes the required input current. At this time, the SR latch resets and M1 turns off. When M1 turns off, DE reverts to a standard, high-impedance CMOS input. The MAX13448E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps. Line Length The Telecommunications Industry Association (TIA) publishes the document TSB-89: Application Guidelines for TIA/EIA-485-A that is a good reference for determining maximum data rate vs. line length. Typical Applications The MAX13448E transceivers are designed for bidirectional data communications on multipoint bus transmission lines. Figure 10 shows a typical network application circuit. To minimize reflections, terminate the line at both ends in its characteristic impedance, and keep stub lengths off the main line as short as possible. Applications Information 256 Transceivers on the Bus The RS-485 standard specifies the load each receiver places on the bus in terms of unit loads. An RS-485 compliant transmitter can drive 32 one-unit loads when used with a 120Ω cable that is terminated on both ends over a common-mode range of -7V to +12V. The ______________________________________________________________________________________ 13 MAX13448E MAX13448E is specified as 1/8 unit loads. This means a compliant transmitter can drive up to 256 MAX13448E devices. Reducing the common mode and/or changing the characteristic impedance of the cable changes the maximum number of receivers that can be used. Refer to the TIA/EIA-485 specification for further details. MAX13448E ±80V Fault-Protected Full-Duplex RS-485 Transceiver A Y 120Ω R RO RE DE 120Ω DI Z Z DI D B B 120Ω D 120Ω R Y DE RE RO A Y Z B A Y Z B R D DI A R MAX13448E D DE RE RO DI DE RE RO Figure 10. Typical Full-Duplex RS-485 Network Pin Configuration Chip Information PROCESS: BiCMOS TOP VIEW N.C. 1 + 14 VCC RO 2 RE 3 13 N.C. MAX13448E 12 A DE 4 11 B DI 5 10 Z GND 6 9 Y GND 7 8 N.C. SO Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 14 SO S14-5 21-0041 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. 14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.