Datasheet

5
LTC1387
PI FU CTIO S
U
UU
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.
V
EE
(Pin 11): Charge Pump Negative Supply Output.
Requires an external 0.1µF 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 100µs with 0.1µF
capacitors). A low logic state at the ON, DXEN and RXEN
inputs will put the transceiver and charge pump in shut-
down mode and reduces I
CC
to 5µA. Whenever the trans-
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.
D
Z
/SLEW (Pin 14): Driver Z or Slew Input. In RS232
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 5µA pull-
up during RS485 mode.
D
Y
(Pin 15): Driver Y Input. Input Y in RS232 mode; the
differential driver input in RS485 mode.
R
B
(Pin 16): Receiver B Output. Output B in RS232 mode;
output is high impedance in RS485 mode.
R
A
(Pin 17): Receiver A Output. Output A in RS232 mode;
the differential receiver output in RS485 mode.
V
CC
(Pin 18): Positive Supply. 4.75V ≤ V
CC
≤ 5.25V.
Requires an external 0.1µF bypass capacitor to ground.
C2
–
(Pin 19): Commutating Capacitor C2 Negative Termi-
nal. Requires an external 0.1µF capacitor between Pins 19
and 20.
C2
+
(Pin 20): Commutating Capacitor C2 Positive
Terminal.