Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control

Transcription

1 19-74; Rev ; 1/7 EVLUTION KIT VILBLE Half-uplex RS-485-/RS-422-Compatible General escription The +5V, half-duplex, ±15kV ES-protected RS-485/RS-422-compatible transceivers feature one driver and one receiver. The MX13487E/ MX13488E include a hot-swap capability to eliminate false transitions on the bus during power-up or live insertion. The feature Maxim s proprietary utoirection control. This architecture makes the devices ideal for applications, such as isolated RS-485 ports, where the driver input is used in conjunction with the driver-enable signal to drive the differential bus. The MX13487E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free transmission up to 5kbps. The MX13488E driver slew rate is not limited, allowing transmit speeds up to 16Mbps. The feature a 1/4-unit load receiver input impedance, allowing up to 128 transceivers on the bus. These devices are intended for halfduplex communications. ll driver outputs are protected to ±15kV ES using the Human Body Model. The are available in an 8-pin SO package. The devices operate over the extended -4 C to +85 C temperature range. Isolated RS-485 Interfaces Utility Meters Industrial Controls Industrial Motor rives utomated HVC Systems pplications Features +5V Operation utoirection Enables river utomatically on Transmission Hot-Swappable for Telecom pplications Enhanced Slew-Rate Limiting Facilitates Error- Free ata Transmission (MX13487E) High-Speed Version (MX13488E) llows for Transmission Speeds Up to 16Mbps Extended ES Protection for RS-485 I/O Pins ±15kV Human Body Model 1/4-Unit Load, llowing Up to 128 Transceivers on the Bus 8-Pin SO Package PRT Ordering Information/ Selector Guide PIN- PCKGE SLEW-RTE LIMITE PKG COE MX13487EES+ 8 SO Yes S8-2 MX13488EES+ 8 SO No S8-2 +enotes a lead-free package Note: ll devices operate over the -4 C to +85 C temperature range. 1 2 RE MX13487E MX13488E Functional iagram RE R SHN - V T B 7 Pin Configuration/Typical pplication Circuit appear at end of data sheet. COM + 6 RI STTE MCHINE E 4 GN 5 Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/allas irect! at , or visit Maxim s website at

2 BSOLUTE MXIMUM RTINGS (ll voltages referenced to GN.) Supply Voltage...+6V SHN, RE,...-.3V to +6, B... -8V to +13V Short-Circuit uration (,, B) to GN...Continuous Continuous Power issipation (T = +7 C) 8-Pin SO (derate 5.9mW/ C above +7 C)...471mW Operating Temperature Range...-4 C to +85 C Junction Temperature C Storage Temperature Range C to +15 C Lead Temperature (soldering 1s)...+3 C Stresses beyond those listed under bsolute 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. ELECTRICL CHRCTERISTICS ( = +5V ±5%, T = T MIN to T MX, unless otherwise noted. Typical values are at = +5V and T = +25 C.) (Note 1) RIVER PRMETER SYMBOL CONTIONS MIN TYP MX UNITS R FF = 1Ω, Figure 1 2. ifferential river Output V O R FF = 54Ω, Figure No load river Common-Mode Output Voltage V OC R L = 1Ω or 54Ω, Figure 1 / 2 3 V river isable Threshold V T Figure 2 (Note 2) V Input-High Voltage V IH, SHN, RE 2. V Input-Low Voltage V IL, SHN, RE.8 V Input Current I IN, SHN, RE ±1 µ river Short-Circuit Output Current (Note 3) river Short-Circuit Foldback Output Current (Note 3) RECEIVER Input Current ( and B) Receiver ifferential Threshold Voltage V V OUT +12V I OS -7V V OUT V ( - 1V) V OUT +12V 2 m I OSF -7V V OUT V -2 I, B =, V IN = +12V 25 = GN or +5V V IN = -7V -2 V TH -7V V CM +12V mv Receiver Input Hysteresis ΔV TH V + V B = V 25 mv Output-High Voltage V OH I O = -1.6m, V - V B > V TH Output-Low Voltage V OL I O = 1m, V - V B < -V TH.4 V Tri-State Output Current at Receiver I OZR V V O ±1 µ Receiver Input Resistance R IN -7V V CM +12V 48 kω Receiver Output Short-Circuit Current I OSR V V ±7 ±95 m V m µ V 2

3 ELECTRICL CHRCTERISTICS (continued) ( = +5V ±5%, T = T MIN to T MX, unless otherwise noted. Typical values are at = +5V and T = +25 C.) (Note 1) POWER SUPPLY PRMETER SYMBOL CONTIONS MIN TYP MX UNITS Supply Voltage V Supply Current I CC SHN = 1, RE =, no load 4.5 m Shutdown Supply Current I SHN SHN = 1 µ ES PTECTION ES Protection (, B) ir Gap ischarge IEC (MX13487E) ±15 Human Body Model ±15 ES Protection (ll Other Pins) Human Body Model ±2 kv SWITCHING CHRCTERISTICS MX13487E ( = +5V ±5%, T = T MIN to T MX, unless otherwise noted. Typical values are at = +5V and T = +25 C.) RIVER PRMETER SYMBOL CONTIONS MIN TYP MX UNITS river Propagation elay t PLH 2 1 R L = 11Ω, C L = 5pF, Figures 2 and 3 t PHL 2 1 river ifferential Output Rise or t HL 2 9 R L = 11Ω, C L = 5pF, Figures 2 and 3 Fall Time t LH 2 9 Maximum ata Rate 5 kbps river isable elay t Figure 3 25 ns river Enable from Shutdown to Output High river Enable from Shutdown to Output Low t ZH(SHN) Figure µs t ZL(SHN) Figure µs Time to Shutdown t SHN ns RECEIVER Receiver Propagation elay t RPLH 8 C L = 15pF, Figures 5 and 6 t RPHL 8 Receiver Output Skew t RSKEW C L = 15pF, Figure 6 13 ns Maximum ata Rate 5 kbps Receiver Enable to Output High t RZH Figure 7 5 ns Receiver Enable to Output Low t RZL Figure 7 5 ns Receiver isable Time from High t RHZ Figure 7 5 ns Receiver isable Time from Low t RLZ Figure 7 5 ns Receiver Enable from Shutdown to Output High t RZH (SHN) Figure 8 22 ns kv ns ns ns 3

4 SWITCHING CHRCTERISTICS MX13487E (continued) ( = +5V ±5%, T = T MIN to T MX, unless otherwise noted. Typical values are at = +5V and T = +25 C.) PRMETER SYMBOL CONTIONS MIN TYP MX UNITS Receiver Enable from Shutdown t RZL Figure 8 22 ns to Output Low (SHN) Receiver Enable elay t RE Figure 3 7 ns Time to Shutdown t SHN ns SWITCHING CHRCTERISTICS MX13488E ( = +5V ±5%, T = T MIN to T MX, unless otherwise noted. Typical values are at = +5V and T = +25 C.) RIVER PRMETER SYMBOL CONTIONS MIN TYP MX UNITS river Propagation elay t PLH 5 R L = 11Ω, C L = 5pF, Figures 2 and 3 t PHL 5 river ifferential Output Rise or t HL 15 R L = 11Ω, C L = 5pF, Figures 2 and 3 Fall Time t LH 15 Maximum ata Rate 16 Mbps river isable elay t Figure 3 7 ns river Enable from Shutdown to Output High river Enable from Shutdown to Output Low t ZH(SHN) Figure µs t ZL(SHN) Figure µs Time to Shutdown t SHN ns RECEIVER Receiver Propagation elay t RPLH 8 C L = 15pF, Figures 5 and 6 t RPHL 8 Receiver Output Skew t RSKEW C L = 15pF, Figure 6 13 ns Maximum ata Rate 16 Mbps Receiver Enable to Output High t RZH Figure 7 5 ns Receiver Enable to Output Low t RZL Figure 7 5 ns Receiver isable Time from High t RHZ Figure 7 5 ns Receiver isable Time from Low t RLZ Figure 7 5 ns Receiver Enable from Shutdown to Output High t RZH (SHN) Figure 8 22 ns ns ns ns 4

5 SWITCHING CHRCTERISTICS MX13488E (continued) ( = +5V ±5%, T = T MIN to T MX, unless otherwise noted. Typical values are at = +5V and T = +25 C.) PRMETER SYMBOL CONTIONS MIN TYP MX UNITS Receiver Enable from Shutdown t RZL Figure 8 22 ns to Output Low (SHN) Receiver Enable elay t RE Figure 3 7 ns Time to Shutdown t SHN ns Note 1: ll currents into the device are positive. ll currents out of the device are negative. ll voltages referred to device ground, unless otherwise noted. Note 2: This is a differential voltage from to B that the driving device must see on the bus to disable its driver. Note 3: The short-circuit output current applied 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. ( = +5.V, T = +25 C, unless otherwise noted.) SUPPLY CURRENT (m) SUPPLY CURRENT vs. TEMPERTURE NO LO MX13487Etoc1 OUTPUT CURRENT (m) OUTPUT CURRENT vs. RECEIVER OUTPUT-HIGH VOLTGE Typical Operating Characteristics MX13487Etoc2 OUTPUT CURRENT (m) OUTPUT CURRENT vs. RECEIVER OUTPUT-LOW VOLTGE MX13487Etoc OUTPUT-HIGH VOLTGE (V) OUTPUT-LOW VOLTGE (V) OUTPUT-HIGH VOLTGE (V) RECEIVER OUTPUT-HIGH VOLTGE vs. TEMPERTURE I O = 1m MX13487Etoc4 OUTPUT-LOW VOLTGE (V) RECEIVER OUTPUT-LOW VOLTGE vs. TEMPERTURE I O = 1m MX13487Etoc5 OUTPUT CURRENT (m) FFERENTIL OUTPUT CURRENT vs. FFERENTIL OUTPUT VOLTGE MX13487Etoc OUTPUT VOLTGE (V) 5

6 Typical Operating Characteristics (continued) ( = +5.V, T = +25 C, unless otherwise noted.) FFERENTIL OUTPUT VOLTGE (V) SHUTOWN CURRENT (μ) RIVER FFERENTIL OUTPUT VOLTGE vs. TEMPERTURE R FF = 54Ω SHUTOWN CURRENT vs. TEMPERTURE MX13487Etoc7 MX13487Etoc1 OUTPUT CURRENT (m) RIVER PPGTION ELY (ns) OUTPUT CURRENT vs. TRNSMITTER OUTPUT-HIGH VOLTGE OUTPUT-HIGH VOLTGE (V) RIVER PPGTION vs. TEMPERTURE (MX13487E) R L = 1kΩ t PLH t PHL MX13487Etoc8 MX13487Etoc11 OUTPUT CURRENT (m) RIVER PPGTION ELY (ns) OUTPUT CURRENT vs. TRNSMITTER OUTPUT-LOW VOLTGE OUTPUT-LOW VOLTGE (V) RIVER PPGTION vs. TEMPERTURE (MX13487E) R L = 11Ω t PLH t PHL MX13487Etoc9 MX13487Etoc12 RIVER PPGTION ELY (ns) RIVER PPGTION vs. TEMPERTURE (MX13488E) R L = 1kΩ t PLH MX13487Etoc13 RIVER PPGTION ELY (ns) RIVER PPGTION vs. TEMPERTURE (MX13488E) R L = 11Ω t PLH MX13487Etoc14 PPGTION ELY (ns) RECEIVER PPGTION vs. TEMPERTURE (MX13487E) 6 45 t RPHL 3 15 MX13487Etoc15 t PHL t PHL t RPLH

7 Typical Operating Characteristics (continued) ( = +5.V, T = +25 C, unless otherwise noted.) RECEIVER PPGTION (ns) RECEIVER PPGTION vs. TEMPERTURE (MX13488E) t RPLH t RPHL RECEIVER PPGTION (16Mbps) (MX13488E) MX13487Etoc16 RIVER PPGTION (5kbps) (MX13487E) MX13487Etoc19 4ns/div B 2V/div MX13487Etoc17 2V/div -B 5V/div RIVER PPGTION (16Mbps) (MX13488E) 1ns/div RIVING 16nF (19.2kbps) (MX13487E) WVEFORM INTENSITY: 68% MX13487Etoc2 2V/div MX13487Etoc18 2V/div -B 5V/div 2V/div 2V/div -B 5V/div 1ns/div 1μs/div RIVING 16nF (19.2kbps) (MX13488E) RIVING 16nF (75kbps) (MX13488E) MX13487Etoc21 2V/div MX13487Etoc22 2V/div -B 5V/div -B 5V/div 1μs/div 4ns/div 7

8 V O CL B Figure 1. river C Test Load B R FF 2 R FF 2 V OC RE = f = 1MHz, t LH 3ns, t HL 3ns 1.5V 1.5V Test Circuits and Waveforms B V I Figure 2. river-timing Test Circuit t PLH t PHL 1/2 V O R L GN R L C L V O 1/2 V O t, t RE V FF O V O -V O ( PULLE LOW) 1% 9% V FF = V() - V(B) 9% 1% tlh t HL Figure 3. river Propagation elays 8

9 OUTPUT UNER TEST C L 5Ω Figure 4. river Enable and isable Times S 1 S 2 Test Circuits and Waveforms (continued) SHN 1.5V t ZL(SHN), B V OL, B 2.3V OUTPUT NORMLLY LOW OUTPUT NORMLLY HIGH 2.3V t ZH(SHN) B TE V I R RECEIVER OUTPUT Figure 5. Receiver-Propagation-elay Test Circuit f = 1MHz, t LH 3ns, t HL 3ns 1V B -1V t RPHL t RPLH V OH 1.5V 1.5V V OL t RSKEW = t RPHL - t RPLH Figure 6. Receiver Propagation elays 9

10 RE = V Figure 7. Receiver Enable and isable Times Test Circuits and Waveforms (continued) 1.5V 1.5V t RZL(SHN), t RZL t RHZ 2.3V OUTPUT NORMLLY LOW OUTPUT NORMLLY HIGH 2.3V t RZH(SHN), t RZH t RHZ V OH +.5V V OH +.5V SHN 1.5V t RZL(SHN) = 1 C L 5Ω S 1 S 2 2.3V OUTPUT NORMLLY LOW OUTPUT NORMLLY HIGH 2.3V t RZH(SHN) Figure 8. Receiver Enable Time from Shutdown 1

11 PIN NME FUNCTION 1 2 RE 3 SHN 4 5 GN Ground Pin escription Receiver Output. When receiver is enabled and V() - V(B) > +2mV, is high. If V() - V(B) < -2mV, is low. Receiver Output Enable. rive RE low to enable the. rive RE high to let the utoirection circuit control the receiver. RE is a hot-swap input (see the Hot-Swap Capability section for more details). Shutdown. rive SHN high to let the device operate in normal operation. rive SHN low to put the part in shutdown. river Input. rive low to force noninverting output low and inverting output high. rive high to force noninverting output high and inverting output low. is an input to the internal state machine that automatically enables and disables the driver. See the Function Tables and General escription for more information. is a hot-swap input (see the Hot-Swap Capability section for more details). 6 Noninverting Receiver Input and Noninverting river Output 7 B Inverting Receiver Input and Inverting river Output 8 Positive Supply, = +5V ±5%. Bypass to GN with a.1µf capacitor. Function Tables TRNSMITTING INPUTS OUTPUTS SHN -B > V T CTION B 1 X Turn driver ON False If driver was OFF, keep it OFF HIGH IMPENCE HIGH IMPENCE 1 1 False If driver was ON, keep it ON True Turn driver OFF HIGH IMPENCE HIGH IMPENCE X X X SHUTOWN RECEIVING INPUTS OUTPUT SHN RE -B RIVER STTE RECEIVER STTE 1 +2mV X ON 1 1-2mV X ON 1 1 X ON OFF HIGH IMPENCE mV OFF ON mV OFF ON X X X X SHUTOWN X = on t care, shutdown mode, driver, and receiver outputs are in high impedance. 11

12 etailed escription The half-duplex, high-speed transceivers for RS-485/RS-422 communication contain one driver and one receiver. The MX13487E/ MX13488E feature a hot-swap capability allowing line insertion without erroneous data transfer (see the Hot- Swap Capability section). The MX13487E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free transmission up to 5kbps. The MX13488E driver slew rate is not limited, making data throughput of up to 16Mbps possible. utoirection Circuitry Internal circuitry in the, in conjunction with an external pullup resistor on and pulldown resistor on B (see Typical pplication Circuit), act to automatically disable or enable the driver and receiver to keep the bus in the correct state. This utoirection circuitry consists of a state machine and an additional receive comparator that determines whether this device is trying to drive the bus, or another node on the network is driving the bus. The internal state machine has two inputs: The current state of -B (determined by a dedicated differential comparator) The state machine also has two outputs: RIVER_ENBLE Internal signal that enables and disables the driver RECEIVER_ENBLE Internal signal that is the inverse of the RIVER_ENBLE signal, but it can be overridden by an external pin When is low, the device always drives the bus low. When is high, the device drives the bus for a short time, then disables the driver and allows the external pullup/pulldown resistors to hold the bus in the high state (-B > 2mV). uring each low-to-high transition of, the driver stays enabled until (-B) > V T, and then disables the driver, letting the pullup/pulldown resistors hold the and B lines in the correct state. Pullup and Pulldown Resistors The pullup and pulldown resistors on the and B lines are required for proper operation of the device although their exact value is not critical. They function to hold the bus in the high state (-B > 2mV) following a low-to-high transition. Sizing of these resistors is determined in the same way as when using any other RS-485 driver and depends on how the line is terminated and how many nodes are on the bus. The most important factor when sizing these resistors is to guarantee that the idle voltage on the bus (-B) is greater than 2mV in order to remain compatible with standard RS-485 receiver thresholds. Idle State When not transmitting data, the MX13487E/ MX13488E require the input be driven high to remain in the idle state. conventional RS-485 transceiver has E and RE inputs that are used to enable and disable the driver and receiver. However, the does not have a E input, and instead uses an internal state machine to enable and disable the drivers. must be driven high in order to go to the idle state. Hot-Swap Capability Hot-Swap Inputs When circuit boards are inserted into a hot or powered back plane, 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. uring this period, the processor s logic-output drivers are high impedance and are unable to drive the and RE inputs of these devices to a defined logic level. Leakage currents up to ±1µ 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. dditionally, parasitic circuit-board capacitance could cause coupling of or GN to the enable inputs. Without the hot-swap capability, these factors could improperly enable the transceiver s driver. To overcome both these problems, two different pullup switches (strong and weak) are turned on during the power-up. When rises, an internal power-up signal enables a strong pullup circuit. It holds and RE high with 1m for 15µs. Once the timeout is expired, this strong pullup is switched off. weak pullup (1µ) remains active to overcome leakage on the pin. This second weak pullup disappears as soon as the microcontroller forces a low state on these pins. Therefore, in normal operation (after the first activation), these pins can be considered as high-impedance pins (CMOS inputs) without any pullup circuitry. The utoirection state machine is initialized, forcing the driver disabled. The receiver is enabled in utoirection mode. Hot-Swap Input Circuitry The enable inputs feature hot-swap capability. t the input there are two pmos devices, M1 and M2 (Figure 9). When ramps from zero, an internal 15µs timer turns 12

13 on M2 and sets the SR latch, which also turns on M1. Transistors M2, a 1.5m current source, and M1, a 5µ current source, pull RE to through a 5kΩ resistor. M2 is designed to pull RE to the disabled state against an external parasitic capacitance up to 1pF that can drive RE high. fter 15µs, the timer deactivates M2 while M1 remains on, holding high against three-state leakages that can drive RE low. M1 remains on until an external source overcomes the required input current. t this time, the SR latch resets and M1 turns off. When M1 turns off, RE reverts to a standard, high-impedance CMOS input. Whenever drops below 1V, the hot-swap input is reset. has similar hot-swap circuitry. ±15kV ES Protection s with all Maxim devices, ES-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 have extra protection against static electricity. Maxim s engineers have developed state-of-the-art structures to protect these pins against ES of ±15kV without damage. The ES structures withstand high ES in all states: normal operation, shutdown, and powered down. fter an ES event, the keep working without latchup or damage. ES protection can be tested in various ways. The transmitter outputs and receiver inputs of the are characterized for protection to the following limits: ±15kV using the Human Body Model ±15kV using the ir Gap ischarge Method specified in IEC (MX13487E only) ES Test Conditions ES 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 1a shows the Human Body Model, and Figure 1b shows the current waveform it generates when discharged into a low impedance. This model consists of a 1pF capacitor charged to the ES voltage of interest, which is then discharged into the test device through a 1.5kΩ resistor. IEC The IEC standard covers ES testing and performance of finished equipment. However, it does not specifically refer to integrated circuits. The help you design equipment to RE TIMER TIMER 5kΩ M1 1μ 5μ 15μs M2 SR LTCH RE (HOT SWP) Figure 9. Simplified Structure of the Receiver Enable Pin (RE) meet IEC without the need for additional ES-protection components. The major difference between tests done using the Human Body Model and IEC is higher peak current in IEC because series resistance is lower in the IEC model. Hence, the ES withstand voltage measured to IEC is generally lower than that measured using the Human Body Model. Figure 1c shows the IEC model, and Figure 1d shows the current waveform for IEC ES Contact ischarge test. Machine Model The machine model for ES tests all pins using a 2pF 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. The ir-gap test involves approaching the device with a charged probe. The Contact-ischarge method connects the probe to the device before the probe is energized. 13

14 HIGH- VOLTGE C SOURCE R C 1MΩ CHRGE-CURRENT- LIMIT RESISTOR Cs 1pF R 15Ω SCHRGE RESISTNCE STORGE CPCITOR Figure 1a. Human Body ES Test Model MPS I P 1% 9% 36.8% 1% t RL Ir TIME t L CURRENT WVEFORM EVICE UNER TEST PEK-TO-PEK RINGING (NOT RWN TO SCLE) HIGH- VOLTGE C SOURCE R C 5MΩ TO 1MΩ CHRGE-CURRENT- LIMIT RESISTOR Cs 15pF R 33Ω SCHRGE RESISTNCE STORGE CPCITOR Figure 1c. IEC ES Test Model IPEK I 1% 9% 1% t r =.7ns TO 1ns 3ns 6ns EVICE UNER TEST t Figure 1b. Human Body Current Waveform Figure 1d. IEC ES Generator Current Waveform pplications Information 128 Transceivers on the Bus The standard RS-485 receiver input impedance is 12kΩ (1-unit load), and the standard driver can drive up to 32-unit loads. The have a 1/4- unit load receiver input impedance (48kΩ), allowing up to 128 transceivers to be connected in parallel on one communication line. ny combination of these devices, 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 MX13487E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission up to 5kbps. Low-Power Shutdown Mode Low-power shutdown mode is initiated by bringing SHN low. In shutdown, the devices draw a maximum of 1µ of supply current. The devices are guaranteed not to enter shutdown if SHN is low for less than 5ns. If the inputs are in this state for at least 7ns, the devices are guaranteed to enter shutdown. Enable times t ZH and t ZL (see the Switching Characteristics section) assume the devices were not in a lowpower shutdown state. Enable times t ZH(SHN) and t ZL(SHN) assume the devices were in shutdown state. It takes drivers and receivers longer to become enabled from low-power shutdown mode (t ZH(SHN), t ZL(SHN) ) than from driver/receiver-disable mode (t ZH, t ZL ). Line Length The RS-485/RS-422 standard covers line lengths up to 4ft. 14

15 SHN RE R MX13487E MX13488E Typical pplications The transceivers are designed for half-duplex, bidirectional data communications on multipoint bus transmission lines. Figure 11 shows a typical network application. 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 MX13487E is more tolerant of imperfect termination. Isolated RS-485 Interface n isolated RS-485 interface electrically isolates different nodes on the bus to protect the bus from problems due to high common-mode voltages that exceed the RS-485 common-mode voltage range, conductive noise, and ground loops. The Typical pplication R t Figure 11. Typical Half-uplex RS-485 Network R SHN RE SHN RE Circuit shows an isolated RS-485 interface using the. The transceiver is powered separately from the controlling circuitry. The utoirection feature of the (see the utoirection Circuitry section), replaces an external relay allowing faster switching speeds, no contact bounce, better reliability, and better electrical isolation. The only require two optocouplers to electrically isolate the transceiver. PCESS: BiCMOS R R t R Chip Information SHN RE 15

16 V SYS RX V SYS TX Pin Configuration/Typical pplication Circuit V ISO.1μF + 1 R 8 V ISO V ISO RE B 2 7 Rt SHN SO GN 16

17 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 N 1 TOP VIEW E H C INCHES MILLIMETERS M MIN MX MIN MX B C e.5 BSC 1.27 BSC E H L VRITIONS: M INCHES MILLIMETERS MIN MX MIN MX N MS B C SOICN.EPS e B 1 FNT VIEW L SIE VIEW -8 PPRIETRY INFORMTION TITLE: PCKGE OUTLINE,.15" SOIC PPVL OCUMENT CONTL NO. REV B 1 1 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, 12 San Gabriel rive, Sunnyvale, C Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc. Boblet