13

LTC1321/LTC1322/LTC1335

SWITCHI G WAVEFOR S

Figure 12. Receiver Enable and Disable Times

S

APPLICATI

I FOR ATIO

Basic Theory of Operation

The LTC1321/LTC1322/LTC1335 each have two interface

ports. Each port may be configured as single-ended EIA562

transceiver(s) or differential RS485 transceiver by forcing

the port’s selection input to a LOW or HIGH, respectively.

The LTC1321 provides one EIA562 driver and one EIA562

receiver per port to maintain same pinout as SP301. The

LTC1322 and LTC1335 each provide two drivers and two

receivers per port. Additionally, the LTC1321 and LTC1322

All the interface drivers feature three-state outputs. Inter-

face outputs are forced into high impedance when the driver

is disabled, in the shutdown mode, or with the power off.

All the interface driver outputs are fault protected by a

current limiting and thermal shutdown circuit. The thermal

shutdown circuit disables both the EIA562 and RS485

driver outputs when the die temperature reaches 150

°C.

The thermal shutdown circuit enables the drivers when the

die temperature cools to 135

°C.

In RS485 mode, shutdown mode or with the power off,

the input resistance of the receiver is 24k. The input

resistance drops to 6.3k in EIA562 mode.

A logic LOW at the ON/OFF pin shuts down the device

and forces all the outputs into a high impedance state.

A logic HIGH enables the device. An internal 4

µAcurrent

In RS485 mode, an internal 4

µA current source pulls

the driver enable pin HIGH if left open. The RS485

receiver has a 4

µA current source at the noninverting

input. If both the RS485 receiver inputs are open, the

output is a high state. Both the current sources are

disabled in the EIA562 mode.

For LTC1335, a logic LOW at the OE pin enables all the

receiver outputs and a logic HIGH disables all the

receiver outputs. An internal 4

µA current source pulls

the OE pin LOW if left open.

A loopback mode enables internal connections from

driver outputs to receiver inputs for self-test when the

1.5V

3V

0V

OE

1.5V

R

5V

0.5V

OUTPUT NORMALLY LOW

0V

1321/22/35 F12

1.5V

1.5V

OUTPUT NORMALLY HIGH

0.5V

R

Figure 11. EIA/TIA-562 Receiver Propagation Delays

A OR B

R

1321/22/35 F11

2.4V

0.8V

1.3V

1.7V