10

LTC1387

S

APPLICATI

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 100

µs 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.

0.1

µF capacitors.

A

B

Y

Z

ON

RXEN

DXEN

485/232

CONTROLLER

DX/RX

RXEN

DXEN

MODE

INTERFACE

A

B

RS232

RS485

RS485

RS232

RS232

RS485

RS485

SHUTDOWN

TRANSMIT MODE

RECEIVE MODE

TRANSMIT MODE

RECEIVE MODE

MODE

RXEN = 0

RXEN = 1

RXEN = 0

RXEN = 1

RXEN = 0

DXEN = 1

DXEN = 0

DXEN = 1

DXEN = 0

DXEN = 0

MODE = 0

MODE = 0

MODE = 1

MODE = 1

MODE = X

1387 • F13

LTC1387

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