5

LTC1387

PI FU CTIO S

485/232 (Pin 8): Interface Mode Select Input. A low logic

input enables two RS232 drivers and two RS232 receiv-

ers. A high input enables the RS485 driver and the RS485

receiver.

DXEN (Pin 9): Driver Enable Input. A high logic input

enables the drivers and a low logic input disables the

drivers. When disabled, all driver outputs are in high

impedance

GND (Pin 10): Ground.

Requires an external 0.1

µF capacitor to ground.

RXEN (Pin 12): Receiver Enable Input. A high logic input

enables the receivers and a low logic input disables the

receivers. When disabled, all receiver outputs are in high

impedance.

ON (Pin 13): A high logic level at ON input keeps the charge

pump active regardless of the state of the DXEN and RXEN

inputs. When the charge pump is active, the drivers and

receivers can be enabled or disabled without waiting for

charge pump stabilization time (typically 100

µswith0.1µF

capacitors). A low logic state at the ON, DXEN and RXEN

inputs will put the transceiver and charge pump in shut-

ceiver is activated from shutdown, the charge pump

should be allowed to stabilize before data transmission.

When DXEN and RXEN are high and ON is low, the charge

pump, drivers and receivers are all active and the driver

outputs are internally looped back to the inputs of the

receiver. The three control inputs ON, DXEN and RXEN can

be configured for one-, two- or three-wire control: one-

wire mode – all three inputs connected together; two-wire

mode – inputs ON and RXEN connected to one wire, DXEN

a separate wire; three-wire mode – separate wires to each

input. See the Function Tables.

mode, this pin is the driver Z input. In RS485 mode, this

pin controls the slew rate of the RS485 driver. With the

SLEW pin high, the RS485 driver runs at maximum (fast)

slew rate and can transmit signals up to 5MBd. With the

SLEW pin low, the RS485 driver runs with reduced (slow)

slew rate to control reflections with improperly terminated

cables. In slow mode, the RS485 driver can support data

rates up to 150kBd. This SLEW pin has internal 5

µA pull-

up during RS485 mode.

differential driver input in RS485 mode.

output is high impedance in RS485 mode.

the differential receiver output in RS485 mode.

Requires an external 0.1

µF bypass capacitor to ground.

nal. Requires an external 0.1

µF capacitor between Pins 19

and 20.

(Pin 20): Commutating Capacitor C2 Positive

Terminal.