Datasheet

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5 V Low Power

EIA RS-485 Transceiver

ADM485

Rev. F

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FEATURES

Meets EIA RS-485 standard

5 Mbps data rate

Single 5 V supply

–7 V to +12 V bus common-mode range

High speed, low power BiCMOS

Thermal shutdown protection

Short-circuit protection

Driver propagation delay: 10 ns typical

Receiver propagation delay: 15 ns typical

High-Z outputs with power off

Superior upgrade for LTC485

APPLICATIONS

Low power RS-485 systems

DTE/DCE interface

Packet switching

Local area networks (LNAs)

Data concentration

Data multiplexers

Integrated services digital network (ISDN)

FUNCTIONAL BLOCK DIAGRAM

GND

ADM485

00078-001

Figure 1.

GENERAL DESCRIPTION

The ADM485 is a differential line transceiver suitable for high

speed bidirectional data communication on multipoint bus

transmission lines. It is designed for balanced data transmission

and complies with EIA standards RS-485 and RS-422. The part

contains a differential line driver and a differential line receiver.

Both the driver and the receiver can be enabled independently.

When disabled, the outputs are three-stated.

The ADM485 operates from a single 5 V power supply.

Excessive power dissipation caused by bus contention or by

output shorting is prevented by a thermal shutdown circuit. If

during fault conditions, a significant temperature increase is

detected in the internal driver circuitry, this feature forces the

driver output into a high impedance state.

Up to 32 transceivers can be connected simultaneously on a

bus, but only one driver should be enabled at any time. It is

important, therefore, that the remaining disabled drivers do not

load the bus. To ensure this, the ADM485 driver features high

output impedance when disabled and when powered down,

which minimizes the loading effect when the transceiver is not

being used. The high impedance driver output is maintained

over the common-mode voltage range of −7 V to +12 V.

The receiver contains a fail-safe feature that results in a logic

high output state if the inputs are unconnected (floating).

The ADM485 is fabricated on BiCMOS, an advanced mixed

technology process combining low power CMOS with fast

switching bipolar technology. All inputs and outputs contain

protection against ESD; all driver outputs feature high source

and sink current capability. An epitaxial layer is used to guard

against latch-up.

The ADM485 features extremely fast switching speeds. Minimal

driver propagation delays permit transmission at data rates up

to 5 Mbps while low skew minimizes EMI interference.

The part is fully specified over the commercial and industrial

temperature range and is available in 8-lead PDIP, 8-lead SOIC,

and small footprint, 8-lead MSOP packages.

Summary of content (16 pages)

PAGE 1
5 V Low Power EIA RS-485 Transceiver ADM485 Meets EIA RS-485 standard 5 Mbps data rate Single 5 V supply –7 V to +12 V bus common-mode range High speed, low power BiCMOS Thermal shutdown protection Short-circuit protection Driver propagation delay: 10 ns typical Receiver propagation delay: 15 ns typical High-Z outputs with power off Superior upgrade for LTC485 FUNCTIONAL BLOCK DIAGRAM ADM485 RO 1 8 VCC RE 2 7 B DE 3 6 A 5 GND DI 4 R D 00078-001 FEATURES Figure 1.
PAGE 2
ADM485 TABLE OF CONTENTS Features .............................................................................................. 1 Test Circuits..................................................................................... 10 Applications....................................................................................... 1 Switching Characteristics .............................................................. 11 Functional Block Diagram ........................................................
PAGE 3
ADM485 SPECIFICATIONS VCC = 5 V ± 5%, all specifications TMIN to TMAX, unless otherwise noted. Table 1.
PAGE 4
ADM485 TIMING SPECIFICATIONS VCC = 5 V ± 5%, all specifications TMIN to TMAX, unless otherwise noted. Table 2.
PAGE 5
ADM485 ABSOLUTE MAXIMUM RATINGS TA = 25°C, unless otherwise noted. Table 4. Transmitting Table 3.
PAGE 6
ADM485 RO 1 RE 2 ADM485 8 VCC 7 B TOP VIEW DE 3 (Not to Scale) 6 A DI 4 5 GND 00078-002 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS Figure 2. Pin Configuration Table 6. Pin Function Descriptions Pin No. 1 2 3 Mnemonic RO RE DE 4 DI 5 6 7 8 GND A B VCC Function Receiver Output. When enabled, if A is greater than B by 200 mV, RO is high. If A is less than B by 200 mV, RO is low. Receiver Output Enable. A low level enables the receiver output, RO.
PAGE 7
ADM485 TYPICAL PERFORMANCE CHARACTERISTICS 0.40 50 I = 8mA 35 30 25 20 15 10 5 0.25 0.50 0.75 1.00 1.25 1.50 1.75 RECEIVER OUTPUT LOW VOLTAGE (V) 2.00 0.20 90 –2 80 –4 70 OUTPUT CURRENT (mA) 0 –6 –8 –10 –12 4.50 4.75 5.00 RECEIVER OUTPUT HIGH VOLTAGE (V) 125 0 0 Figure 4. Output Current vs. Receiver Output High Voltage 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V) 4.5 Figure 7. Output Current vs. Driver Differential Output Voltage 4.
PAGE 8
ADM485 0.7 100 90 0.6 0.5 RECEIVER SKEW (ns) OUTPUT CURRENT (mA) 80 70 60 50 40 30 | tPLH – tPHL | 0.4 0.3 0.2 20 0.1 0 0.5 4.0 1.0 1.5 2.0 2.5 3.0 3.5 DRIVER OUTPUT LOW VOLTAGE (V) 4.5 0 –50 00078-009 0 Figure 9. Output Current vs. Driver Output Low Voltage –25 0 25 50 75 TEMPERATURE (°C) 100 125 00078-012 10 Figure 12. Receiver Skew vs. Temperature 0 6 –10 5 –30 –40 DRIVER SKEW (ns) –50 –60 –70 –80 4 3 | tPHLA – tPHLB | 2 –90 1 –110 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.
PAGE 9
ADM485 T DI 4 T A A B B 1,2 CH2 1.00VΩ BW M5.00ns CH3 2.64V RO CH1 1.00VΩ BW CH3 5.00VΩ BW Figure 15. Unloaded Driver Differential Outputs CH2 1.00VΩ BW M10.00ns CH4 2.00VΩBW CH4 2.76V Figure 18. Driver/Receiver Propagation Delays, High to Low A A B B CH1 1.00VΩBW CH2 500mVΩ BW M5.00ns CH3 00078-016 1,2 2.74V 1,2 CH1 500mVΩ Figure 16. Loaded Driver Differential Outputs T A 4 B RO 1,2 CH4 400mV 00078-017 3 CH2 1.00VΩ BW M10.0ns CH4 2.00VΩBW M10.00ns Figure 19.
PAGE 10
ADM485 TEST CIRCUITS VCC R A 0V OR 3V CL B 00078-020 VOC R RL S1 DE S2 VOUT 00078-023 VOD DE IN Figure 20. Driver Voltage Measurement Figure 23. Driver Enable/Disable 375Ω A VTST CL Figure 24. Receiver Propagation Delay Figure 21. Driver Voltage Measurement VCC +1.5V A CL1 S1 RLDIFF CL2 RL RE CL 00078-022 B –1.5V VOUT REIN Figure 25. Receiver Enable/Disable Figure 22. Driver Propagation Delay Rev.
PAGE 11
ADM485 SWITCHING CHARACTERISTICS 3V 1.5V 0V 1.5V tPLH B tPHL A, B 0V tSKEW = tPLH – tPHL tPLH tPHL +VO VOH 90% POINT 90% POINT RO 10% POINT 10% POINT tR tF 1.5V 1.5V tSKEW = tPLH – tPHL 00078-026 0V VOL Figure 28. Receiver Propagation Delay Figure 26. Driver Propagation Delay, Rise/Fall Timing 3V 3V 1.5V tZL 0V tHZ 2.3V 1.5V RO VOH – 0.5V VOL tHZ OUTPUT HIGH VOH 0V VOL + 0.5V OUTPUT LOW tZH 00078-027 tZH tLZ VOL + 0.5V VOL A, B 1.5V 1.5V tZL 0V tLZ 2.
PAGE 12
ADM485 APPLICATIONS INFORMATION DIFFERENTIAL DATA TRANSMISSION RT D Table 7. Comparison of RS-422 and RS-485 Interface Standards Specification Transmission Type Maximum Cable Length Minimum Driver Output Voltage Driver Load Impedance Receiver Input Resistance Receiver Input Sensitivity Receiver Input Voltage Range No. of Drivers/Receivers per Line RS-422 Differential 4000 ft. ±2 V 100 Ω 4 kΩ min ±200 mV −7 V to +7 V 1/10 RS-485 Differential 4000 ft. ±1.
PAGE 13
ADM485 OUTLINE DIMENSIONS 5.00 (0.1968) 4.80 (0.1890) 5 1 6.20 (0.2441) 5.80 (0.2284) 4 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) 1.75 (0.0688) 1.35 (0.0532) 0.51 (0.0201) 0.31 (0.0122) COPLANARITY 0.10 SEATING PLANE 0.50 (0.0196) 0.25 (0.0099) 8° 0° 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.
PAGE 14
ADM485 0.400 (10.16) 0.365 (9.27) 0.355 (9.02) 8 5 1 4 0.280 (7.11) 0.250 (6.35) 0.240 (6.10) 0.100 (2.54) BSC 0.210 (5.33) MAX 0.060 (1.52) MAX 0.015 (0.38) MIN 0.150 (3.81) 0.130 (3.30) 0.115 (2.92) SEATING PLANE 0.022 (0.56) 0.018 (0.46) 0.014 (0.36) 0.325 (8.26) 0.310 (7.87) 0.300 (7.62) 0.195 (4.95) 0.130 (3.30) 0.115 (2.92) 0.015 (0.38) GAUGE PLANE 0.005 (0.13) MIN 0.430 (10.92) MAX 0.014 (0.36) 0.010 (0.25) 0.008 (0.
PAGE 15
ADM485 NOTES Rev.