19-5652; Rev 1; 7/11 +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver Features The MAX14780E +5.0V, ±30kV ESD-protected, RS-485/ RS-422 transceiver features one driver and one receiver. The device includes fail-safe circuitry, guaranteeing a logic-high receiver output when receiver inputs are open or shorted. The receiver outputs a logic-high if all transmitters on a terminated bus are disabled (high impedance). The MAX14780E includes a hot-swap capability to eliminate false transitions on the bus during power-up or hot insertion. S +5.0V Operation The MAX14780E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps. S Low-Current Shutdown Mode The MAX14780E is ideal for half-duplex communications and it draws 1.2mA of supply current when unloaded or when fully loaded with the drivers disabled. The MAX14780E has a 1/8-unit load receiver input impedance, allowing up to 256 transceivers on the bus. S Extended ESD Protection for RS-485/RS-422 I/O Pins ±30kV Human Body Model S True Fail-Safe Receiver While Maintaining EIA/ TIA-485 Compatibility S Hot-Swap Input Structures on DE and RE S Enhanced Slew-Rate Limiting Facilitates ErrorFree Data Transmission S Allow Up to 256 Transceivers on the Bus S Available in Industry-Standard 8-Pin SO and PDIP Packages The MAX14780E is available in an 8-pin SO and PDIP packages. Ordering Information Applications Utility Meters PART TEMP RANGE PIN-PACKAGE Lighting Systems MAX14780EESA+ -40NC to +85NC 8 SO Industrial Control MAX14780EEPA+ -40NC to +85NC 8 PDIP Telecom +Denotes a lead(Pb)-free/RoHS-compliant package. Security Systems Instrumentation Profibus Typical Operating Circuit 0.1µF RO RE DE DI 1 + R 8 2 7 3 6 4 D 5 MAX14780E DE VCC D B A Rt DI B Rt A GND RO R RE TYPICAL HALF-DUPLEX OPERATING CIRCUIT ________________________________________________________________ Maxim Integrated Products 1 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. MAX14780E General Description MAX14780E +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver ABSOLUTE MAXIMUM RATINGS (All voltages referenced to GND.) Supply Voltage (VCC)............................................................ +6V Control Input Voltage (RE, DE)................................-0.3V to +6V Driver Input Voltage (DI)..........................................-0.3V to +6V Driver Output Voltage (A, B).....................................-8V to +13V Receiver Input Voltage (A, B)...................................-8V to +13V Receiver Output Voltage (RO).................. -0.3V to (VCC + 0.3V) Driver Output Current..................................................... ±250mA Continuous Power Dissipation (TA = +70°C) SO (derate 5.9mW/°C above +70°C)...........................471mW PDIP (derate 9.1mW/°C above +70°C) .....................727.3mW 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 Soldering Temperature (reflow).......................................+260°C 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 = +5.0V ±10%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5.0V and TA = +25NC.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS V DRIVER VCC Supply-Voltage Range Differential Driver Output Change in Magnitude of Differential Output Voltage Driver Common-Mode Output Voltage Change in Magnitude of Common-Mode Voltage Input-High Voltage Input-Low Voltage Input Hysteresis Input Current VCC VOD DVOD VOC DVOC 5.5 3 VCC RL = 54I (RS-485), Figure 1 2 VCC VCC RL = 100I or 54I, Figure 1 (Note 2) 0.2 V 3 V 0.2 V RL = 100I or 54I, Figure 1 (Note 2) VIL DE, DI, RE VHYS DE, DI, RE IIN1 DE, DI, RE IOSD Driver Short-Circuit Foldback Output Current IOSDF Thermal-Shutdown Threshold TTS Thermal-Shutdown Hysteresis TTSH VCC/2 RL = 100I or 54I, Figure 1 DE, DI, RE Driver Short-Circuit Output Current V No load VIH Input Impedance First Transition Input Current (A and B) 4.5 RL = 100I (RS-422), Figure 1 3 V 0.8 100 V mV Q1 FA DE, RE 0 P VOUT P +12V (Note 3) 1 10 kI 40 250 -7V P VOUT P VCC (Note 3) -250 -40 (VCC - 1V) P VOUT P +12V (Note 3) 20 -20 -7V P VOUT P +1V (Note 3) 175 IA, B VTH -7V P VCM P +12V VIN = +12V VIN = -7V mA NC 15 VDE = 0V, VCC = 0V or VCC mA NC 125 -100 FA RECEIVER Receiver Differential Threshold Voltage Receiver Input Hysteresis DVTH VA + VB = 0V -200 -125 15 2 _______________________________________________________________________________________ -50 mV mV +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver (VCC = +5.0V ±10%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5.0V and TA = +25NC.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP VCC 0.6 MAX UNITS RO Output-High Voltage VOH IO = -1mA V RO Output-Low Voltage VOL IO = 1mA 0.4 V Three-State Output Current at Receiver IOZR 0 P VO P VCC P1 FA Receiver Input Resistance RIN -7V P VCM P +12V Receiver Output Short-Circuit Current IOSR 0V P VRO P VCC 96 kI P 110 mA SUPPLY CURRENT Supply Current ICC Supply Current in Shutdown Mode ISHDN No load, VRE = 0V, DE = VCC 1.2 1.8 No load, RE = VCC, DE = VCC No load, VRE = 0V, VDE = 0V 1.2 1.8 1.2 1.8 RE = VCC, VDE = 0V 2.8 10 Human Body Model Q30 Contact Discharge IEC 61000-4-2 Q12 Air-Gap Discharge IEC 61000-4-2 Q15 mA FA ESD PROTECTION ESD Protection for A and B kV DRIVER SWITCHING CHARACTERISTICS WITH INTERNAL SRL (500kbps) (VCC = +5.0V ±10%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5.0V and TA = +25NC.) (Note 1) PARAMETER Driver Propagation Delay Driver Differential Output Rise or Fall Time Differential Driver Output Skew |tDPLH - tDPHL| SYMBOL tDPLH tDPHL CONDITIONS CL = 50pF, RL = 54I, Figures 2 and 3 tR , tF CL = 50pF, RL = 54I, Figures 2 and 3 tDSKEW CL = 50pF, RL = 54I, Figures 2 and 3 Maximum Data Rate MIN TYP MAX UNITS 200 1000 200 1000 250 900 ns 140 ns 500 ns kbps Driver Enable to Output High tDZH Figure 4 2500 ns Driver Enable to Output Low tDZL Figure 5 2500 ns Driver Disable Time from Low tDLZ Figure 5 100 ns Driver Disable Time from High tDHZ Figure 4 100 ns Driver Enable from Shutdown to Output High tDZH(SHDN) Figure 4 5500 ns Driver Enable from Shutdown to Output Low tDZL(SHDN) Figure 5 5500 ns 700 ns Time to Shutdown tSHDN 50 340 _______________________________________________________________________________________ 3 MAX14780E DC ELECTRICAL CHARACTERISTICS (continued) MAX14780E +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver RECEIVER SWITCHING CHARACTERISTICS WITH INTERNAL SRL (500kbps) (VCC = +5.0V ±10%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5.0V and TA = +25NC.) (Note 1) PARAMETER SYMBOL tRPLH Receiver Propagation Delay tRPHL Receiver Output Skew |tRPLH - tRPHL| tRSKEW CONDITIONS MIN TYP MAX UNITS 200 CL = 15pF, Figures 6 and 7 ns 200 CL = 15pF, Figures 6 and 7 30 Maximum Data Rate 500 ns kbps Receiver Enable to Output Low tRZL Figure 8 50 ns Receiver Enable to Output High tRZH Figure 8 50 ns Receiver Disable Time from Low tRLZ Figure 8 50 ns Receiver Disable Time from High tRHZ Figure 8 50 ns Receiver Enable from Shutdown to Output High tRZH(SHDN) Figure 8 5500 ns Receiver Enable from Shutdown to Output Low tRZL(SHDN) Figure 8 5500 ns 700 ns Time to Shutdown tSHDN 50 340 Note 1: All currents into the device are positive. All currents out of the device are negative. All voltages are referred to device ground, unless otherwise noted. Note 2: ΔVOD and ΔVOC are the changes in VOD and VOC, respectively, when the DI input changes state. Note 3: 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 recovery from bus contention. Test Circuits and Waveforms B VCC DI RL/2 0 VCC/2 tDPLH VOD RL/2 tDPHL Z VOC Y A VO 1/2 VO VO VDIFF 0 -VO Figure 1. Driver DC Test Load VCC 10% VDIFF = V (B) - V (A) 90% 90% tF tR tSKEW = | tDPLH - tDPHL | DE Figure 3. Driver Propagation Delays B DI VOD 1/2 VO RL CL A Figure 2. Driver Timing Test Circuit 4 _______________________________________________________________________________________ 10% +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver S1 D 0 OR VCC OUT RL = 500Ω CL 50pF GENERATOR 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 RL = 500Ω S1 0 OR VCC D OUT CL 50pF GENERATOR 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 (tDZL, tDLZ, tDLZ(SHDN)) _______________________________________________________________________________________ 5 MAX14780E Test Circuits and Waveforms (continued) MAX14780E +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver Test Circuits and Waveforms (continued) RECEIVER OUTPUT B VID ATE R A +1V B -1V tRPLH VOH A RO tRPHL VCC/2 VOL THE RISE TIME AND FALL TIME OF INPUTS A AND B < 4ns Figure 6. Receiver Propagation Delay Test Circuit Figure 7. Receiver Propagation Delays S1 +1.5V S3 VCC 1kΩ -1.5V VID CL 15pF GENERATOR S2 50Ω S1 OPEN S2 CLOSED VS3 = +1.5V S1 CLOSED S2 OPEN VS3 = -1.5V VCC VCC VCC/2 RE RE 0 0 tRZH, tRZH(SHDN) tRZL, tRZL(SHDN) VOH RO VCC VOH / 2 (VOL + VCC)/2 RO 0 S1 OPEN S2 CLOSED VS3 = +1.5V RE 50% VOL S1 CLOSED S2 OPEN VS3 = -1.5V VCC VCC/2 tRHZ 50% 0 VCC VCC/2 RE 0 tRLZ 0.25V 10% VCC VOH RO 0 RO 10% 0.25V Figure 8. Receiver Enable and Disable Times 6 _______________________________________________________________________________________ VOL +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver 1.30 1.20 DE = VCC 1.10 DE = 0 1.00 0.80 40 30 20 MAX14780E toc03 50 40 30 20 10 0 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 1 2 3 4 0 5 0 1 2 3 4 5 OUTPUT LOW VOLTAGE (V) RECEIVER OUTPUT-HIGH VOLTAGE vs. TEMPERATURE RECEIVER OUTPUT-LOW VOLTAGE vs. TEMPERATURE DRIVER DIFFERENTIAL OUTPUT CURRENT vs. DIFFERENTIAL OUTPUT VOLTAGE 5.0 4.8 4.6 4.4 0.7 4.2 0.6 0.5 0.4 0.3 0.2 0.1 4.0 160 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 MAX14780E toc06 IO = 1mA DIFFERENTIAL OUTPUT CURRENT (mA) 5.2 0.8 OUTPUT LOW VOLTAGE (V) IO = -1mA MAX14780E toc05 OUTPUT HIGH VOLTAGE (V) MAX14780E toc04 TEMPERATURE (°C) 5.4 140 120 100 80 60 40 20 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 0 1 2 3 4 5 TEMPERATURE (°C) TEMPERATURE (°C) DIFFERENTIAL OUTPUT VOLTAGE (V) DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE OUTPUT CURRENT vs. TRANSMITTER OUTPUT-HIGH VOLTAGE OUTPUT CURRENT vs. TRANSMITTER OUTPUT-LOW VOLTAGE 4.0 3.6 3.2 2.8 2.4 2.0 160 140 120 100 80 60 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) 180 160 140 120 100 80 60 40 40 20 20 0 -40 -25 -10 200 0 -7 -6 -5 -4 -3 -2 -1 0 1 2 OUTPUT HIGH VOLTAGE (V) 3 4 5 MAX14780E toc09 180 OUTPUT CURRENT (mA) 4.4 200 OUTPUT CURRENT (mA) RL = 54Ω MAX14780E toc07 4.8 MAX14780E toc08 OUTPUT HIGH VOLTAGE (V) 60 10 0.90 DIFFERENTIAL OUTPUT VOLTAGE (V) 70 OUTPUT CURRENT (mA) 1.40 50 OUTPUT CURRENT (mA) SUPPLY CURRENT (mA) 1.50 60 MAX14780E toc02 NO LOAD MAX14780E toc01 1.60 OUTPUT CURRENT vs. RECEIVER OUTPUT-LOW VOLTAGE OUTPUT CURRENT vs. RECEIVER OUTPUT-HIGH VOLTAGE SUPPLY CURRENT vs. TEMPERATURE 0 2 4 6 8 10 12 OUTPUT-LOW VOLTAGE (V) _______________________________________________________________________________________ 7 MAX14780E Typical Operating Characteristics (VCC = +5.0V, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VCC = +5.0V, TA = +25°C, unless otherwise noted.) 7 6 5 4 3 2 1 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 tDPHL 500 tDPLH 450 400 350 300 MAX14780E toc12 550 180 RECEIVER PROPAGATION DELAY (ns) 8 600 MAX14780E toc11 9 DRIVER PROPAGATION DELAY (ns) MAX14780E toc10 10 RECEIVER PROPAGATION DELAY vs. TEMPERATURE (500kbps) DRIVER PROPAGATION DELAY vs. TEMPERATURE (500kbps) SHUTDOWN CURRENT vs. TEMPERATURE SHUTDOWN CURRENT (µA) MAX14780E +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver 160 140 120 100 tDPLH 80 60 tDPHL 40 20 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) -40 -25 -10 TEMPERATURE (°C) RECEIVER PROPAGATION DELAY (500kbps) TEMPERATURE (°C) DRIVER PROPAGATION DELAY (500kbps) MAX14780E toc14 MAX14780E toc13 RL = 100Ω RL = 100Ω DI 2V/div VA - VB 5V/div RO 2V/div 200ns/div 5 20 35 50 65 80 95 110 125 VY - VZ 5V/div 400ns/div 8 _______________________________________________________________________________________ +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver + RO 1 R RE 2 DE 3 DI 4 D 8 VCC 7 B 6 A 5 GND SO/PDIP Pin Description PIN NAME FUNCTION 1 RO Receiver Output. When RE is low and if (A - B) R -50mV, RO is high; if (A - B) P -200mV, RO is low. 2 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. RE is a hot-swap input (see the Hot-Swap Capability section for details). 3 DE Driver Output Enable. Drive DE high to enable driver outputs. These outputs are high impedance when DE is low. Drive RE high and DE low to enter low-power shutdown mode. DE is a hot-swap input (see the Hot-Swap Capability section for details). 4 DI Driver Input. With DE high, a low on DI forces noninverting output low and inverting output high. Similarly, a high on DI forces noninverting output high and inverting output low. 5 GND 6 A Noninverting Receiver Input and Noninverting Driver Output 7 B Inverting Receiver Input and Inverting Driver Output 8 VCC Ground Positive Supply VCC = +5.0V Q10%. Bypass VCC to GND with a 0.1FF capacitor. Function Tables TRANSMITTING INPUTS RECEIVING OUTPUTS INPUTS OUTPUTS RE X DE DI B A A-B RO 1 0 1 RE 0 DE 1 X R -50mV 1 X 1 0 1 0 0 X P -200mV 0 0 0 X High-Z High-Z 0 X Open/shorted 1 1 0 X 1 1 X High-Z 1 0 X Shutdown Shutdown _______________________________________________________________________________________ 9 MAX14780E Pin Configuration MAX14780E +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver Detailed Description The MAX14780E high-speed transceiver for RS-485/ RS-422 communication contains one driver and one receiver. This device features fail-safe circuitry, which guarantees a logic-high receiver output when the receiver inputs are open or shorted, or when they are connected to a terminated transmission line with all drivers disabled (see the Fail-Safe section). The MAX14780E also features a hot-swap capability allowing line insertion without erroneous data transfer (see the Hot-Swap Capability section). The MAX14780E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps. The MAX14780E is a half-duplex transceiver and operates from a single +5.0V supply. Drivers are output short-circuit current limited. Thermal-shutdown circuitry protects drivers against excessive power dissipation. When activated, the thermal-shutdown circuitry places the driver outputs into a high-impedance state. Fail-Safe The MAX14780E 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 receiver input 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 threshold of the MAX14780E, this results in a logic-high with a 50mV minimum noise margin. Unlike previous fail-safe devices, the -50mV to -200mV threshold complies with the ±200mV EIA/TIA485 standard. Additionally, parasitic circuit board 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 and RE high. After the initial power-up sequence, the pulldown circuit becomes transparent, resetting the hot-swap tolerable input. 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, which also turns on M1. Transistors M2, a 1.5mA current sink, and M1, a 500μA 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 VCC 10µs TIMER SR LATCH TIMER Hot-Swap Capability Hot-Swap Inputs When circuit boards are inserted into a hot or powered backplane, differential 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 logic-output drivers are high impedance and are unable to drive the DE and RE inputs of these devices 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. 5kΩ DE (HOT SWAP) DE 100µA 500µA M1 M2 Figure 9. Simplified Structure of the Driver Enable Pin (DE) 10 ������������������������������������������������������������������������������������� +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver For RE there is a complementary circuit employing two pMOS devices pulling RE to VCC. ±30kV 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 output and receiver input of the MAX14780E have extra protection against static electricity. Maxim’s engineers have developed state-of-the-art structures to protect these pins against ESD of ±30kV without damage. The ESD structures withstand high ESD in all states: normal operation, shutdown, and powered down. After an ESD event, the MAX14780E keeps working without latchup or damage. ESD protection can be tested in various ways. The transmitter output and receiver input of the MAX14780E are characterized for protection to the following limits: • ±30kV using the Human Body Model • ±12kV using the Contact Discharge method specified in IEC 61000-4-2 • ±15kV using the Air-Gap Discharge method specified in IEC 61000-4-2 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. RC 1MΩ CHARGE-CURRENTLIMIT RESISTOR HIGHVOLTAGE DC SOURCE Cs 100pF RD 1500Ω IEC 61000-4-2 The IEC 61000-4-2 standard covers ESD testing and performance of finished equipment. However, it does not specifically refer to integrated circuits. The MAX14780E helps you design equipment to meet IEC 61000-4-2, without the need for additional ESD-protection components. The major difference between tests done using the Human Body Model and IEC 61000-4-2 is higher peak current in IEC 61000-4-2 because series resistance is lower in the IEC 61000-4-2 model. Hence, the ESD withstand voltage measured to IEC 61000-4-2 is generally lower than that measured using the Human Body Model. Figure 10c shows the IEC 61000-4-2 model, and Figure 10d shows the current waveform for IEC 61000‑4‑2 ESD Contact Discharge test. Machine Model The machine model for ESD tests all pins using a 200pF storage capacitor and zero discharge resistance. The objective is to emulate the stress caused when I/O pins are contacted by handling equipment during test and assembly. Of course, all pins require this protection, not just RS-485 inputs and outputs. IP 100% 90% DISCHARGE RESISTANCE STORAGE CAPACITOR Human Body Model Figure 10a shows the Human Body Model, and Figure 10b 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. Ir AMPS DEVICE UNDER TEST 36.8% 10% 0 0 Figure 10a. Human Body ESD Test Model PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE) tRL TIME tDL CURRENT WAVEFORM Figure 10b. Human Body Current Waveform ______________________________________________________________________________________ 11 MAX14780E CMOS input. Whenever VCC drops below 1V, the hotswap input is reset. RC 50MΩ TO 100MΩ CHARGE-CURRENTLIMIT RESISTOR HIGHVOLTAGE DC SOURCE Cs 150pF RD 330Ω I 100% 90% DISCHARGE RESISTANCE STORAGE CAPACITOR IPEAK MAX14780E +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver DEVICE UNDER TEST 10% tr = 0.7ns TO 1ns t 30ns 60ns Figure 10c. IEC 61000-4-2 ESD Test Model Applications Information The standard RS-485 receiver input impedance is 12kΩ (1-unit load), and the standard driver can drive up to 32-unit loads. The MAX14780E has a 1/8-unit load receiver input impedance (96kΩ), allowing up to 256 transceivers to be connected in parallel on one communication line. Any combination of the MAX14780E, as well as other RS-485 transceivers with a total of 32-unit loads or fewer, can be connected to the line. Reduced EMI and Reflections The MAX14780E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps. Low-Power Shutdown Mode Low-power shutdown mode is initiated by bringing both RE high and DE low. In shutdown, the devices typically draw only 2.8μA of supply current. RE and DE can be driven simultaneously; the devices are guaranteed not to enter shutdown if RE is high and DE is low for less than 50ns. If the inputs are in this state for at least 700ns, the devices are guaranteed to enter shutdown. Figure 10d. IEC 61000-4-2 ESD Generator Current Waveform Enable times tZH and tZL (see the Switching Characteristics section) assume the devices were not in a low-power shutdown state. Enable times tZH(SHDN) and tZL(SHDN) assume the devices were in shutdown state. It takes drivers and receivers longer to become enabled from low-power shutdown mode (tZH(SHDN), tZL(SHDN)) than from driver/receiver-disable mode (tZH, tZL). 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 +175°C (typ). Line Length The RS-485/RS-422 standard covers line lengths up to 4000ft. For line lengths greater than 4000ft, it may be necessary to implement a line repeater. 12 ������������������������������������������������������������������������������������� +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver 120Ω B DI DE B D D DI DE RO A B A B A A R R RO RE RE R R D D MAX14780E DI DE RO RE DI DE RO RE Figure 11. Typical Half-Duplex RS-485 Network Package Information Typical Applications The MAX14780E transceiver is designed for bidirectional data communications on multipoint bus transmission lines. Figure 11 shows a typical network applications 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. The slew-rate-limited MAX14780E is more tolerant of imperfect termination. Chip Information PROCESS: BiCMOS 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. 8 SO S8+4 21-0041 90-0096 8 PDIP P8+2 21-0043 — ______________________________________________________________________________________ 13 MAX14780E 120Ω MAX14780E +5.0V, ±30kV ESD-Protected, Fail-Safe, Hot-Swap, RS-485/RS-422 Transceiver Revision History REVISION NUMBER REVISION DATE 0 12/10 Initial release 1 7/11 Added PDIP package information to data sheet DESCRIPTION PAGES CHANGED — 1, 2 , 9, 13 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 © 2011 Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.