LTC1387 View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC1387

Single 5V RS232/RS485 Multiprotocol Transceiver

Linear Technology 

LTC1387

APPLICATI S I FOR ATIO

EMI and signal reflection problems. Slow slew rate sys-

tems can often use improperly terminated or even

unterminated cables with acceptable results. The RS485

differential input receiver features an offset input thresh-

old of – 80mV at 0V common mode voltage. This allows

the receiver output to have a known High output state

when the inputs are open or shorted. The receiver also

features an input hysteresis of 40mV. The charge pump

can be kept active regardless of the state of DXEN and

RXEN pins by keeping the ON pin High. This improves the

receiver response time by removing the 100µs charge

pump start-up time.

In RS232 mode, the drivers and receivers can be selected

from the Function Tables with control inputs ON, RXEN

and DXEN. The receivers feature a typical 0.6V input

hysteresis.

All the interface driver outputs are fault protected by a

current limiting and thermal shutdown circuit. The thermal

shutdown circuit disables both the RS232 and RS485

driver outputs when the die temperature reaches 150°C.

The thermal shutdown circuit reenables the drivers when

the die temperature cools to 135°C.

A loopback mode enables internal connections from driver

outputs to receiver inputs for self-test. The driver outputs

are not isolated from the external loads during loopback.

The charge pump generates boosted positive voltage VDD

and negative voltage VEE for true RS232 levels from a

single 5V VCC supply. The charge pump requires four

0.1µF capacitors.

RS232 RS485

A

A

INTERFACE

B

RS485

B

Y

Z

LTC1387

RA

RB

DY

DZ

RA

RB

DY

DZ/SLEW VCC

ON

RXEN

DXEN

485/232

DX/RX

CONTROLLER

RXEN

DXEN

MODE

RS232

TRANSMIT MODE

RXEN = 0

DXEN = 1

MODE = 0

RS232

RECEIVE MODE

RXEN = 1

DXEN = 0

MODE = 0

RS485

TRANSMIT MODE

RXEN = 0

DXEN = 1

MODE = 1

RS485

RECEIVE MODE

RXEN = 1

DXEN = 0

MODE = 1

SHUTDOWN

MODE

RXEN = 0

DXEN = 0

MODE = X

1387 • F13

Figure 13. Half-Duplex RS232 (1-Channel), Half-Duplex RS485

10

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