6

LTC1320

S

APPLICATI

I FOR ATIO

Thermal Shutdown Protection

The LTC1320 includes a thermal shutdown circuit which

protects the part against prolonged shorts at the driver

outputs. If any driver output is shorted to another output

or to the power supply, the current will be initially limited

to 450mA max. The die temperature will rise to about

150

°C, at which point the thermal shutdown circuit turns

off the driver outputs. When the die cools to about 130

°C,

the outputs re-enable. If the shorted condition still exists,

the part will heat again and the cycle will repeat. When the

short is removed, the part will return to normal operation.

This oscillation occurs at about 10Hz and prevents the part

from being damaged by excessive power dissipation.

Power Shutdown

The power shutdown feature of the LTC1320 is designed

primarily for battery-powered systems. When SD (pin 4)

is forced high, the part enters shutdown mode. In shut-

down, the supply current drops from 1.2mA to 30

µA typ.

The driver outputs are three-stated and the power to the

receivers is removed. The receiver outputs are not auto-

matically three-stated in shutdown, and can toggle errone-

ously due to feedthrough from the inputs. This can be

prevented by pulling RXEN high along with SD; this will

three-state the receiver outputs and prevent the genera-

tion of spurious data.

Supply Bypassing

bypassed; data errors can result from inadequate bypass-

ing. Bypass capacitor values of 0.1

and trace lengths between the capacitors and the chip

should be short to minimize lead inductance.

S

APPLICATI

TYPICAL

Single 5V Supply

RS422 to RS562/RS562 to RS422 Converter

17

1

18

0.1

µF

5V

914

0.1

µF

DRIVER I/O

LTC1320 • TA03

16

2

15

3

13

4

12

5

11

6

10

7

8

LTC1320

100

µF

LTC1046

LT1054

*

+

8

5

+

2

4

10

µF

2

µF

3

LOGIC I/O

5V

*LTC1046 GIVES 300

µA QUIESCENT

CURRENT WHEN LTC1320 IS SHUT DOWN

LT1054 PROVIDES HIGHER OUTPUT DRIVE

1N5817

15

11

18

0.1

µF

5V

914

LTC1320 • TA04

6

10

13

8

16

2

17

12

3

7

4

1

LTC1320

0.1

µF

5

–5V

RS562 OUT

NC

NC

+

–

RS422 OUT

+

–

RS562 IN

RS422 IN

TXO

RXI

RXO

SD

RXEN

TXDEN

RXDO

TXI

RXO

TXD

RXI

GND