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19-2441; Rev 0; 4/02
60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection
General Description
The MAX3443E fault-protected RS-485/RS-422 transceiver features 60V protection from signal faults on communication bus lines. Each device contains one differential line driver with three-state output, and one differential line receiver with three-state input. The 1/4-unit-load receiver input impedance allows up to 128 transceivers on a single bus. The device operates from a 5V supply at data rates up to 10Mbps. True fail-safe inputs guarantee a logic-high receiver output when the receiver inputs are open, shorted, or connected to an idle data line. Hot-swap circuitry eliminates false transitions on the data cable during circuit initialization or connection to a live backplane. Short-circuit current limiting and thermal shutdown circuitry protect the driver against excessive power dissipation, and integrated 15kV ESD protection eliminates costly external protection devices. The MAX3443E is available in 8-pin SO and PDIP packages, and is specified over commercial, industrial, and automotive temperature ranges. o 60V Fault Protection o 15kV ESD Protection o Guaranteed 10Mbps Data Rate o Allows Up to 128 Transceivers on the Bus o -7V to +12V Common-Mode Input Range o True Fail-Safe Receiver Inputs o Hot-Swap Inputs for Telecom Applications o Automotive Temperature Range (-40C to +125C) o Industry-Standard Pinout
Features
MAX3443E
Ordering Information
PART MAX3443ECSA MAX3443ECPA MAX3443EESA MAX3443EEPA MAX3443EASA MAX3443EAPA TEMP RANGE 0C to +70C 0C to +70C -40C to +85C -40C to +85C -40C to +125C -40C to +125C PIN-PACKAGE 8 SO 8 PDIP 8 SO 8 PDIP 8 SO 8 PDIP
Applications
RS-422/RS-485 Communications Industrial Networks Telecommunication Systems Automotive Applications HVAC Controls
Pin Configuration and Typical Operating Circuit
TOP VIEW
MAX3443E
RO 1 R 8 7 6 D 5 VCC B A GND RO 1 R 8 VCC 7B Rt 6 A 5 GND
DE D B Rt A R RE RO DI
RE 2 DE DI 3 4
RE 2 DE DI 3 4 D
DIP/SO
________________________________________________________________ Maxim Integrated Products
1
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection MAX3443E
ABSOLUTE MAXIMUM RATINGS
All Voltages Referenced with Respect to GND VCC ........................................................................................+7V RE, DE, DI...................................................-0.3V to (VCC + 0.3V) A, B (Note 1) ........................................................................60V RO ..............................................................-0.3V to (VCC + 0.3V) Continuous Power Dissipation (TA = +70C) 8-Pin SO (derate 5.9mW/C above +70C)..................471mW 8-Pin PDIP (derate 9.09mW/C above +70C).............727mW Operating Temperature Ranges MAX3443EC_ _ ..................................................0C to +70C MAX3443EE_ _ ...............................................-40C to +85C MAX3443EA_ _ .............................................-40C to +125C Storage Temperature Range .............................-65C to +150C Short-Circuit Duration (RO, A, B) ...............................Continuous Lead Temperature (soldering, 10s) .................................+300C
Note 1: A, B must be terminated with 54 or 100 to guarantee 60V fault protection.
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 = +4.75V to +5.25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.)
PARAMETER DRIVER Differential Driver Output Change in Magnitude of Differential Output Voltage Driver Common-Mode Output Voltage Change In Magnitude of Common-Mode Voltage DRIVER LOGIC Driver Input High Voltage Driver Input Low Voltage Driver Input Current Driver Output Fault Current Driver Short-Circuit Output Current Driver Short-Circuit Foldback Output Current RECEIVER DE = GND, VCC = GND, VA, B = +12V VA, B = -7V VA, B = 60V Receiver Differential Threshold Voltage Receiver Input Hysteresis VTH VTH -7V VCM +12V -200 25 250 -150 6 -50 mA mV mV A VDIH VDIL IDIN IOFC IOSD IOSDF VA, B = 60V, RL = 54 -7V VOUT +12V (Note 3) -7V VOUT +12V (Note 3) 2.0 0.8 2 6 350 25 V V A mA mA mA VOD VOD VOC VOC Figure 1, RL = 50 Figure 1, RL = 27 Figure 1, RL = 50 or 27 (Note 2) Figure 1, RL = 50 or 27 Figure 1, RL = 50 or 27 (Note 2) VCC / 2 2.0 1.5 VCC VCC 0.2 3 0.2 V V V V SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Current
IA,B
A, B
2
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection
DC ELECTRICAL CHARACTERISTICS (continued)
(VCC = +4.75V to +5.25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.)
PARAMETER RECEIVER LOGIC Output High Voltage Output Low Voltage Three-State Output Current at Receiver Receiver Input Resistance Receiver Output Short-Circuit Current CONTROL Control Input High Voltage Input Current DE Current Latch During First DE Rising Edge Input Current RE Current Latch During First RE Falling Edge VCIH DE, RE 2.0 90 90 V A A VOH VOL IOZR RIN IOSR Figure 2, IOH = -1.6mA Figure 2, IOL = 1mA 0 VA, B VCC -7V VCM +12V 0 VRO VCC 48 95 VCC - 0.6 0.4 1 V V A k mA SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX3443E
PROTECTION SPECIFICATIONS
(VCC = +4.75V to +5.25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.)
PARAMETER Overvoltage Protection SYMBOL CONDITIONS A, B RSOURCE = 0, RL = 54 IEC 1000-4-2 Air-Gap Discharge ESD Protection A, B IEC 1000-4-2 Contact Discharge Human Body Model SUPPLY CURRENT Normal Operation Supply Current in Shutdown Mode Supply Current with Output Shorted with 60V IQ ISHDN ISHRT No load, DI = VCC or GND, RE = GND, DE = VCC DE = GND, RE = VCC DE = GND, RE = GND, output in three-state 10 10 15 mA A mA MIN 60 2 8 15 kV TYP MAX UNITS V
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection MAX3443E
SWITCHING CHARACTERISTICS (DRIVER)
(VCC = +4.75V to +5.25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.)
PARAMETER Driver Propagation Delay Driver Differential Propagation Delay Driver Differential Output Transition Time Driver Output Skew SYMBOL tPLHA, tPLHB tDPLH, tDPHL tLH, tHL tSKEWAB, tSKEWBA tDSKEW fMAX tPDZH tPDHZ tPDHS tPDZL tPDLZ tPDLS tSHDN Figure 5, RL = 500, CL = 50pF Figure 5, RL = 500, CL = 50pF Figure 5, RL = 500, CL = 50pF Figure 6, RL = 500, CL = 50pF Figure 6, RL = 500, CL = 50pF Figure 6, RL = 500, CL = 50pF RL = 500, CL = 50pF CONDITIONS Figure 3, RL = 27, CL = 50pF Figure 4, RL = 54, CL = 50pF Figure 4, RL = 54, CL = 50pF RL = 54, CL = 50pF, tSKEWAB = |tPLHA - tPHLB|, tSKEWBA = |tPLHB - tPHLA| RL = 54, CL = 50pF, tDSKEW = |tDPLH - tDPHL| 10 1200 1200 4.2 1200 1200 4.2 800 MIN TYP MAX 60 60 25 UNITS ns ns ns
10
ns
Differential Driver Output Skew Maximum Data Rate Driver Enable Time to Output High Driver Disable Time from Output High Driver Wake Time from Shutdown to Output High Driver Enable Time to Output Low Driver Disable Time from Output Low Driver Wake Time from Shutdown to Output Low Time to Shutdown
10
ns Mbps ns ns s ns ns s ns
4
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection
SWITCHING CHARACTERISTICS (RECEIVER)
(VCC = +4.75V to +5.25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.)
PARAMETER Receiver Propagation Delay Receiver Output Skew Receiver Enable Time to Output High Receiver Disable Time from Output High Receiver Wake Time from Shutdown to Output High Receiver Enable Time to Output Low Receiver Disable Time from Output Low Receiver Wake Time from Shutdown to Output Low Time to Shutdown SYMBOL tRPLH, tRPHL tRSKEW tRPZH tRPHZ tRPSH tRPZL tRPLZ tRPSL CONDITIONS Figure 7, CL = 20pF, VID = 2V, VCM = 0 CL = 20pF, tRSKEW = |tRPLH - tRPHL| Figure 8, RL = 1k, CL = 20pF Figure 8, RL = 1k, CL = 20pF Figure 8, RL = 1k, CL= 20pF Figure 8, RL = 1k, CL = 20pF Figure 8, RL = 1k, CL= 20pF Figure 8, RL = 1k, CL= 20pF MIN TYP MAX 75 15 400 400 4.2 400 400 4.2 800 UNITS ns ns ns ns s ns ns s ns
MAX3443E
Note 2: VOD and VOC 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.
Typical Operating Characteristics
(VCC = +5V, TA = +25C, unless otherwise noted.)
NO-LOAD SUPPLY CURRENT vs. TEMPERATURE
MAX3443E toc01
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
MAX3443E toc02
RECEIVER OUTPUT CURRENT vs. OUTPUT LOW VOLTAGE
35 30 25 20 15 10 5
MAX3443E toc03
6 DE = VCC, RE = GND 5 SUPPLY CURRENT (mA) 4 DE = RE = GND 3 2 1 0
10 DE = GND, RE = VCC SUPPLY CURRENT (nA)
40 RECEIVER OUTPUT CURRENT (mA)
1
0.1
0.01 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 OUTPUT LOW VOLTAGE (V)
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection MAX3443E
Typical Operating Characteristics (continued)
(VCC = +5V, TA = +25C, unless otherwise noted.)
RECEIVER OUTPUT CURRENT vs. OUTPUT HIGH VOLTAGE
MAX3443E toc04
RECEIVER OUTPUT VOLTAGE vs. TEMPERATURE
4.5 RECEIVER OUTPUT VOLTAGE (V) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 VOL, IOUT = -10mA VOH, IOUT = +10mA
MAX3443E toc05
DRIVER OUTPUT CURRENT vs. DIFFERENTIAL OUTPUT VOLTAGE
70 DRIVER OUTPUT CURRENT (mA) 60 50 40 30 20 10 0
MAX3443E toc06
40 RECEIVER OUTPUT CURRENT (mA) 35 30 25 20 15 10 5 0
5.0
80
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 OUTPUT HIGH VOLTAGE (V)
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
DIFFERENTIAL OUTPUT VOLTAGE (VA - VB) (V)
DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE
MAX3443E toc07
A, B CURRENT vs. A, B VOLTAGE (TO GROUND)
1600 1200 A, B CURRENT (A) 800 400 0 -400 -800 -1200 -1600 DE = RE = GND -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 A, B VOLTAGE (V) RL = 54
MAX3443E toc08
3.5 DIFFERENTIAL OUTPUT VOLTAGE (V) 3.0 2.5 2.0 RL = 54 1.5 1.0 0.5 0 RL = 100
2000
-2000 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
6
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection
Test Circuits and Waveforms
RL A DI D B VCC VOD RL 2 2
MAX3443E
VOC
Figure 1. Driver VOD and VCC
A VID B 0 VOL IOL (+) VOH IOH (-) R RO
Figure 2. Receiver VOH and VOL
3V VOM
DI
RL = 27 A DI D GENERATOR (NOTE 4) B 50 VCC VOH + VOL 1.5V 2 B CL = 50pF (NOTE 5) A S1
1.5V
1.5V 0
OUT
tPLHA
tPHLA VOH VOM VOM VOL
tPHLB
tPLHB
VOH VOM VOM VOL
VOM =
Figure 3. Driver Propagation Times
3V DI RL = 54 OUT 1.5V 1.5V 0 tDPLH tDPHL 2.0V 50% 10% tHL
DI D GENERATOR (NOTE 4)
A
CL
B 50 VCC CL
90% (A-B) CL = 50pF (NOTE 5) tLH 50% 10%
90%
-2.0V
Figure 4. Driver Differential Output Delay and Transition Times _______________________________________________________________________________________ 7
60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection MAX3443E
Test Circuits and Waveforms (continued)
A DI 0 OR 3V D B DE GENERATOR (NOTE 4) CL = 50pF (NOTE 5) RL = 500W S1 A, B DE 1.5V tPDZH tPDHS 1.5V 0 tPDHZ VOH 3V
509 A, B VOM = VOH + VOL 2 VOM
0.25V
1.5V
0
Figure 5. Driver Enable and Disable Times
VCC 3V A DI 0 OR 3V D B DE GENERATOR (NOTE 4) CL = 50pF (NOTE 5) A, B 50 VOM 0.25V VOL VCC S1 RL = 500 A, B DE 1.5V tPDZL tPDLS 1.5V 0 tPDLZ
Figure 6. Driver Enable and Disable Times
A GENERATOR (NOTE 4) VID 509 B R RO CL = 20pF (NOTE 5) tRPLH tRPHL (A-B) 1.5V 1.5V
3.0V
0
VCC 1.5V 0 RO VOM VOM 0
Figure 7. Receiver Propagation Delay
8
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection
Test Circuits and Waveforms (continued)
1.5V -1.5V S3 VID B CL = 20pF (NOTE 5) GENERATOR (NOTE 4) 509 S1 A R RO 1k9 S2 VCC
MAX3443E
3V RE tRPZH tRPSH VOH RO 1.5V 0 3V RE 1.5V 0 tRPHZ RO 0.5V VOH RO 0 S1 OPEN S2 CLOSED S3 = 1.5V RE 1.5V RO 1.5V 1.5V 0 S1 OPEN S2 CLOSED S3 = 1.5V RE tRPZL tRPSL 1.5V
3V S1 CLOSED S2 OPEN S3 = -1.5V
0
VCC
VOL 3V S1 CLOSED S2 OPEN S3 = -1.5V
0
tRPLZ
0.5V
VCC
VOL
Figure 8. Receiver Enable and Disable Times Note 4: The input pulse is supplied by a generator with the following characteristics: f = 5MHz, 50% duty cycle; tr 6ns; Z0 = 50. Note 5: CL includes probe and stray capacitance.
Pin Description
PIN 1 2 3 4 5 6 7 8 NAME RO RE DE DI GND A B VCC FUNCTION Receiver Output. If RE = low and (A-B) -50mV, RO = high; if (A-B) -200mV, RO = low. Receiver Output Enable. Pull RE low to enable RO. Driver Output Enable. Force DE high to enable driver. Pull DE low to three-state the driver output. Drive RE high and pull DE low to enter low-power shutdown mode. Driver Input. A logic low on DI forces the noninverting output low and the inverting output high. A logic high on DI forces the noninverting output high and the inverting output low. Ground Noninverting Receiver Input/Driver Output with Integrated 15kV ESD Protection Inverting Receiver Input/Driver Output with Integrated 15kV ESD Protection Positive Supply, VCC = +4.75V to +5.25V
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection MAX3443E
Function Tables
MAX3443E (RS-485/RS-422)
TRANSMITTING INPUTS RE 0 0 0 1 1 1 DE 0 1 1 0 1 1 DI X 0 1 X 0 1 A High-Z 0 1 Shutdown 0 1 OUTPUTS B High-Z 1 0 Shutdown 1 0 RE 0 0 0 1 1 X = Don't care. DE X X X 1 0
MAX3443E (RS-485/RS-422)
RECEIVING INPUTS (A-B) 0.2V -0.2V Open/Shorted X X OUTPUT RO 1 0 1 High-Z Shutdown
X = Don't care.
Detailed Description
Driver
The driver accepts a single-ended, logic-level input (DI) and transfers it to a differential, RS-485/RS-422 level output (A and B). Driving DE high enables the driver, while pulling DE low places the driver outputs (A and B) into a high-impedance state (see the transmitting function table).
respect to ground without damage. Protection is guaranteed regardless of whether the device is active, shut down, or without power.
True Fail-Safe
The MAX3443E uses a -50mV to -200mV differential input threshold to ensure true fail-safe receiver inputs. This threshold guarantees the receiver output is a logic high for shorted, open, or idle data lines. The -50mV to -200mV threshold complies with the 200mV threshold specified in the EIA/TIA-485 standard.
Receiver
The receiver accepts a differential, RS-485/RS-422 level input (A and B), and transfers it to a single-ended, logic-level output (RO). Pulling RE low enables the receiver, while driving RE high places the receiver inputs (A and B) into a high-impedance state (see the receiving function table).
15kV ESD Protection
As with all Maxim devices, ESD-protection structures are incorporated on all pins to protect against ESD encountered during handling and assembly. The MAX3443E receiver inputs/driver outputs (A, B) have extra protection against static electricity found in normal operation. Maxim's engineers developed state-ofthe-art structures to protect these pins against 15kV ESD without damage. After an ESD event, the MAX3443E continues working without latchup. ESD protection can be tested in several ways. The receiver inputs are characterized for protection to the following: * 15kV using the Human Body Model * 8kV using the Contact Discharge method specified in IEC 1000-4-2 (formerly IEC 801-2) * 15kV using the Air-Gap Discharge method specified in IEC 1000-4-2 (formerly IEC 801-2) ESD Test Conditions ESD performance depends on a number of conditions. Contact Maxim for a reliability report that documents test setup, methodology, and results.
Low-Power Shutdown
Force DE low and RE high to shut down the MAX3443E. A time delay of 50ns prevents the device from accidentally entering shutdown due to logic skews when switching between transmit and receive modes. Holding DE low and RE high for at least 800ns guarantees that the MAX3443E enters shutdown. In shutdown, the device consumes a maximum of 10A supply current.
60V Fault Protection
The driver outputs/receiver inputs of RS-485 devices in industrial network applications often experience voltage faults resulting from shorts to the power bus that exceed the -7V to +12V range specified in the EIA/TIA485 standard. In these applications, ordinary RS-485 devices (typical absolute maximum -8V to +12.5V) require costly external protection devices. To reduce system complexity and eliminate this need for external protection, the driver outputs/receiver inputs of the MAX3443E withstand voltage faults up to 60V with
10
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection MAX3443E
RC 1M9 CHARGE-CURRENTLIMIT RESISTOR HIGHVOLTAGE DC SOURCE RD 1.5k9 DISCHARGE RESISTANCE DEVICE UNDER TEST IP 100% 90% AMPERES 36.8% 10% 0 0 tRL TIME tDL CURRENT WAVEFORM Ir PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE)
Cs 100pF
STORAGE CAPACITOR
Figure 9a. Human Body ESD Test Model
Figure 9b. Human Body Model Current Waveform
Human Body Model Figure 9a shows the Human Body Model, and Figure 9b 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 device through a 1.5k resistor. IEC 1000-4-2 Since January 1996, all equipment manufactured and/or sold in the European community has been required to meet the stringent IEC 1000-4-2 specification. The IEC 1000-4-2 standard covers ESD testing and performance of finished equipment; it does not specifically refer to integrated circuits. The MAX3443E helps you design equipment that meets Level 4 (the highest level) of IEC 1000-4-2, without additional ESD-protection components. The main difference between tests done using the Human Body Model and IEC 1000-4-2 is higher peak current in IEC 1000-4-2. Because series resistance is lower in the IEC 1000-4-2 ESD test model (Figure 10a), the ESD withstand voltage measured to this standard is generally lower than that measured using the Human
RC 50M TO 100M CHARGE-CURRENTLIMIT RESISTOR HIGHVOLTAGE DC SOURCE RD 330 DISCHARGE RESISTANCE DEVICE UNDER TEST
Body Model. Figure 10b shows the current waveform for the 8kV IEC 1000-4-2 Level 4 ESD Contact Discharge test. The Air-Gap test involves approaching the device with a charge probe. The Contact Discharge method connects the probe to the device before the probe is energized. Machine Model The Machine Model for ESD testing uses a 200pF storage capacitor and zero-discharge resistance. It mimics the stress caused by handling during manufacturing and assembly. All pins (not just RS-485 inputs) require this protection during manufacturing. Therefore, the Machine Model is less relevant to the I/O ports than are the Human Body Model and IEC 1000-4-2.
Driver Output Protection
Two mechanisms prevent excessive output current and power dissipation caused by faults, or bus contention. The first, a foldback current limit on the driver output stage, provides immediate protection against short circuits over the whole common-mode voltage range. The second, a thermal shutdown circuit, forces the driver
I 100% 90% IPEAK
Cs 150pF
STORAGE CAPACITOR
10% tr = 0.7ns TO 1ns 30ns 60ns t
Figure 10a. IEC 1000-4-2 ESD Test Model
Figure 10b. IEC 1000-4-2 ESD Generator Current Waveform 11
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection MAX3443E
outputs into a high-impedance state if the die temperature exceeds +160C. Normal operation resumes when the die temperature cools to +140C, resulting in a pulsed output during continuous short-circuit conditions.
VCC 15s TIMER TIMER
Hot-Swap Capability
Hot-Swap Inputs Inserting circuit boards into a hot, or powered, backplane may cause voltage transients on DE, RE, and receiver inputs A and B that can lead to data errors. For example, upon initial circuit board insertion, the processor undergoes a power-up sequence. During this period, the high-impedance state of the output drivers makes them unable to drive the MAX3443E enable inputs (DE, RE) to a defined logic level. Meanwhile, leakage currents up to 10A from the high-impedance output, or capacitively coupled noise from VCC or GND, could cause an input to drift to an incorrect logic state. To prevent such a condition from occurring, the MAX3443E features hot-swap input circuitry on DE and RE to safeguard against unwanted driver activation during hot-swap situations. When VCC rises, an internal pulldown (or pullup for RE) circuit holds DE low for at least 10s, and until the current into DE exceeds 200A. After the initial power-up sequence, the pulldown circuit becomes transparent, resetting the hotswap tolerable input. Hot-Swap Input Circuitry At the driver enable input (DE), there are two NMOS devices, M1 and M2 (Figure 11). When VCC ramps from zero, an internal 15s timer turns on M2 and sets the SR latch, which also turns on M1. Transistors M2, a 2mA current sink, and M1, a 100A current sink, pull DE to GND through a 5.6k resistor. M2 pulls DE to the disabled state against an external parasitic capacitance up to 100pF that may drive DE high. After 15s, the timer deactivates M2 while M1 remains on, holding DE low against three-state leakage currents that may drive DE high. M1 remains on until an external current source overcomes the required input current. At this time, the SR latch resets M1 and turns off. When M1 turns off, DE reverts to a standard, high-impedance CMOS input. Whenever V CC drops below +1V, the input is reset. A complimentary circuit for RE utilizes two PMOS devices to pull RE to VCC.
DE (HOT SWAP)
5.6k
100A M1
2mA M2
Figure 11. Simplified Structure of the Driver Enable Pin (DE)
Applications Information
128 Transceivers on the Bus
The MAX3443E 1/4-unit-load receiver input impedance (48k) allows up to 128 transceivers connected in parallel on one communication line. Connect any combination of these devices, and/or other RS-485 devices, for a maximum of 32 unit loads to the line.
RS-485 Applications
The MAX3443E transceiver provides bidirectional data communications on multipoint bus transmission lines. Figure 12 shows a typical network applications circuit. The RS-485 standard covers line lengths up to 4000ft. To minimize reflections, and reduce data errors, terminate the signal line at both ends in its characteristic impedance, and keep stub lengths off the main line as short as possible.
J1708 Applications
To configure the MAX3443E in a J1708 application, connect DI and RE to GND. Connect the signal to be transmitted to DE through an inverter. At each transceiver, terminate the bus with the load circuit (shown in Figure 13). When all transceivers are idle in this configuration, all receivers output a logic high because of the pullup resistor on A and pulldown resistor on B. Since RE is connected to GND, all transmitters on the bus listen at
12
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection MAX3443E
120 DI D DE RO RE R R D R B 120 B D DI A B A B A A R RO RE DE
MAX3443E
DI
D
DE
RO RE
DI
DE
RO RE
Figure 12. MAX3443E Typical RS-485 Network
all times. Incoming data on DE enables the driver, which pulls the line low and causes all receivers to output a logic low.
Chip Information
TRANSISTOR COUNT: 310 PROCESS: BiCMOS
VCC Tx DE
R1 4.7k9 DI D B R3 479 C1 2.2nF J1708 BUS
MAX3443E
A Rx RO R
C2 2.2nF R4 479 R2 4.7k9
RE
Figure 13. J1708 Application Circuit
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection MAX3443E
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
SOICN.EPS
14
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60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with 15kV ESD Protection
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
MAX3443E
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 15 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
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