10

LTC1323

APPLICATIO S I FOR ATIO

Driving Differential AppleTalk or Single-Ended Loads

The differential driver is able to drive either an AppleTalk

load or a single-ended load such as a printer or modem.

typically swing between 1.2V and 3.5V (Figure 14a). With

ment of

±3.7V(Figure14b).Anautomaticswitchingcircuit

prevents the differential driver from overloading the charge

pump if the outputs are shorted to ground while driving

single-ended signals. This allows the second single-ended

driver to continue to operate normally when the first is

shorted, and allows external circuitry attached to the charge

pump output to continue to operate even if there are faults

at the driver outputs.

Power Shutdown

The power shutdown feature of the LTC1323 is designed

for battery-powered systems. When SHDN is forced

high the part enters shutdown mode. In shutdown the

supply current typically drops from 2.4mA to 0.5

µA , the

charge pump turns off, and the driver and receiver

outputs are three-stated.

Receiver Keep-Alive Mode (24-Pin SO Wide Only)

The 24-pin SO Wide version of the LTC1323 also features

a power saving receiver keep-alive mode. When CPEN is

pulled high the charge pump is turned off and the outputs

of both drivers, the noninverting single-ended receiver and

the differential receiver are forced into three-state. The

dropping to 65

µA and the receiver delay time increasing to

a maximum of 400ns. The receiver can then be used to

monitor a wake-up control signal.

Charge Pump Capacitors and Supply Bypassing

The LTC1323 requires two external 0.33

µF capacitors for

types and should be mounted as close as possible to the

LTC1323. Monolithic ceramic capacitors work well in this

application. Do not use capacitors greater than 2

µF at the

charge pump pins or internal peak currents can rise to

operation and prevent data errors. A 1

µF capacitor from

tantalum capacitors are adequate for power supply by-

passing; aluminum electrolytic capacitors should only be

used if their ESR is low enough for proper charge pump

operation. Inadequate bypass or charge pump capacitors

will cause the charge pump output to go out of regulation

prematurely, degrading the output swing at the SINGLE-

ENDED driver outputs.

EXTERNAL

CHIP

GND

12

24

21

1

µF

4.7

µF

LTC1323 • F15

–5.5V

13

LTC1323

C1

+

Thermal Shutdown Protection

The LTC1323 includes a thermal shutdown circuit which

protects against prolonged shorts at the driver outputs. If

a driver output is shorted to another output or to the power

supply, the current will be initially limited to a maximum of

500mA. When the die temperature rises above 150

°C, the

thermal shutdown circuit disables the driver outputs.

When the die cools to about 130

°C, the outputs are re-

enabled. If the short still exists, the part will heat again and

the cycle will repeat. This oscillation occurs at about 10Hz

and prevents the part from being damaged by excessive

power dissipation. When the short is removed, the part will

return to normal operation.

Figure 14