LTC2802 datasheet(10/32 Pages) AD

10 / 32 page

LTC2873

REV B

For more information www.analog.com

PIN FUNCTIONS

VEE (Pins 1, 10, 25): Generated Negative Supply Voltage

for RS232 Driver (–6.3V). Tie all pins together and connect

1µF capacitor between VEE (Pin 10) and GND. Exposed

pad (Pin 25) must be soldered to PCB to maintain low

thermal resistance.

RO(Pin2):RS485DifferentialReceiverOutputandRS232

Receiver Output. Logic level referenced to GND and VL.

485/232 (Pin3): Interface Select Input. A logic low enables

RS232 mode and a high enables RS485 mode. The mode

determines which transceiver inputs and outputs are ac-

cessible at the LTC2873 pins. Logic level referenced to

GND and VL. Do not float.

RE485 (Pin4): RS485 Receiver Enable. In RS485 mode, a

logic high disables the RS485 receiver, leaving its output

Hi-Z and a logic low enables the RS485 receiver. This input

has no function in RS232 mode (485/232 low). Logic level

referenced to GND and VL. Do not float.

DE485/F232 (Pin 5): RS485 Driver Enable and RS232 Fast

Mode Enable. In RS485 mode (485/232 high), a logic low

disables the RS485 driver leaving the driver outputs in a

Hi-Z state and a logic high enables the RS485 driver. In

RS232mode(485/232low),alogichighenablesFastmode

with maximum data rate of 1Mbps. A logic low enables

Slow mode with a maximum data rate of 250kbps. Logic

level referenced to GND and VL. Do not float.

DI (Pin 6): RS485 and RS232 Driver Input. Logic level

referenced to GND and VL. Do not float.

SHDN (Pin7): Shutdown Control. A logic low disables the

LTC2873 into low power shutdown state, independent

of the other inputs. Driver and receiver outputs become

Hi-Z. Logic level referenced to GND and VL. Do not float.

GND (Pin 8, 11, 16, 20): Ground. Tie all four pins together.

CAP(Pin9):ChargePumpCapacitorforGeneratedNegative

Supply Voltage VEE. Connect a 220nF capacitor between

CAP and SW.

SW (Pin 12): Switch Pin. Connect 10µH inductor between

SW and VCC. See Inductor Selection section for further

details.

VDD (Pin 13): Generated Positive Supply Voltage for

RS232 Driver (+7.0V). Connect 1µF capacitor between

VDD and GND.

VCC (Pin 14, 18, 21): Input Supply (3V to 5.5V). Tie all

three pins together and connect a 2.2µF or larger capacitor

between VCC (adjacent to VDD) and GND.

B/RI (Pin 15): RS485 Negative Receiver Input and Driver

Output. In RS232 mode, this is the RS232 receiver input.

A/DO (Pin 17): RS485 Positive Receiver Input and Driver

Output. In RS232 mode, this is the RS232 driver output.

NC (Pin 19): Not connected internally.

VL (Pin 22): Logic Supply (1.7V to 5.5V) for the Receiver

Outputs, Driver Inputs, and Control Inputs. Bypass this

pin to GND with a 0.1µF capacitor if not tied to VCC. Keep

VL ≤ VCC for operation guaranteed to meet specifications.

However, VL > VCC will not damage the device, provided

thatabsolutemaximumlimitsarerespected.See“VL Logic

Supply and Logic Pins” in Applications section for more

information.

LB (Pin 23): Loopback Enable. A logic high enables logic

loopback diagnostic mode, internally routing the driver

input logic signals to the receiver output pins. This applies

to RS232 and RS485 operation. The targeted receiver

must be enabled for the loopback signal to be available

on its output. A logic low disables Loopback mode. In

Loopback mode, signals are not inverted from driver

inputs to receiver outputs. Logic level referenced to GND

and VL. Do not float.

TE485(Pin24):RS485TerminationEnable.InRS485mode,

a logic low enables a 120Ω resistor between pins A/DO

and B/RI. A logic high opens the resistor between A/DO

and B/RI, leaving the pins unterminated. In RS485 mode,

the 5k resistor between B/RI and GND is never engaged.

In RS232 mode, the 120Ω resistor between A/DO and B/

RI is never engaged, regardless of the state of TE485, and

the 5k resistor between B/RI and GND is always engaged.

Logic level referenced to GND and VL. Do not float.

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