ISL8483E(2005) Просмотр технического описания (PDF) - Intersil

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производитель

ISL8483E
(Rev.:2005)

ESD Protected to ±15kV, 5V, Low Power, High Speed or Slew Rate Limited, RS-485/RS-422 Transceivers

Intersil 

ISL8483E, ISL8485E

Test Circuits and Waveforms (Continued)

+1.5V

RE

B

A

RO

R

15pF

3V

A

1.5V

1.5V

0V

SIGNAL

GENERATOR

tPLH

tPHL

VCC

RO

50%

50%

0V

FIGURE 4A. TEST CIRCUIT

FIGURE 4B. MEASUREMENT POINTS

FIGURE 4. RECEIVER PROPAGATION DELAY

SIGNAL

GENERATOR

RE

B

A

RO

R

1kΩ

15pF

VCC

SW GND

(SHDN) FOR ISL8483E ONLY

PARAMETER

DE

tHZ

0

tLZ

0

tZH (Note 6)

0

tZL (Note 6)

0

tZH(SHDN) (Note 9)

0

tZL(SHDN) (Note 9)

0

A

+1.5V

-1.5V

+1.5V

-1.5V

+1.5V

-1.5V

SW

GND

VCC

GND

VCC

GND

VCC

NOTE 7

RE

tZH, tZH(SHDN)

NOTE 7

RO

tZL, tZL(SHDN)

NOTE 7

RO

1.5V

3V

1.5V

0V

tHZ

OUTPUT HIGH

1.5V

VOH - 0.5V VOH

0V

tLZ

1.5V

OUTPUT LOW

VCC

VOL + 0.5V VOL

FIGURE 5A. TEST CIRCUIT

FIGURE 5B. MEASUREMENT POINTS

FIGURE 5. RECEIVER ENABLE AND DISABLE TIMES

Application Information

RS-485 and RS-422 are differential (balanced) data

transmission standards for use in long haul or noisy

environments. RS-422 is a subset of RS-485, so RS-485

transceivers are also RS-422 compliant. RS-422 is a point-

to-multipoint (multidrop) standard, which allows only one

driver and up to 10 (assuming one unit load devices)

receivers on each bus. RS-485 is a true multipoint standard,

which allows up to 32 one unit load devices (any

combination of drivers and receivers) on each bus. To allow

for multipoint operation, the RS-485 spec requires that

drivers must handle bus contention without sustaining any

damage.

Another important advantage of RS-485 is the extended

common mode range (CMR), which specifies that the driver

outputs and receiver inputs withstand signals that range from

+12V to -7V. RS-422 and RS-485 are intended for runs as

long as 4000’, so the wide CMR is necessary to handle

ground potential differences, as well as voltages induced in

the cable by external fields.

Receiver Features

These devices utilize a differential input receiver for maximum

noise immunity and common mode rejection. Input sensitivity

is ±200mV, as required by the RS422 and RS-485

specifications.

Receiver input impedance surpasses the RS-422 spec of

4kΩ, and meets the RS-485 “Unit Load” requirement of 12kΩ

minimum.

Receiver inputs function with common mode voltages as

great as ±7V outside the power supplies (i.e., +12V and

-7V), making them ideal for long networks where induced

voltages are a realistic concern.

All the receivers include a “fail-safe if open” function that

guarantees a high level receiver output if the receiver inputs

are unconnected (floating).

8

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