LTC1324(RevA) View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC1324
(Rev.:RevA)

Single Supply LocalTalk® Transceiver

Linear Technology 

LTC1324

SWITCHING WAVEFORMS

3V

RXEN

0V

5V

RXO, RXO, RXDO

VOL

VOH

RXO, RXO, RXDO

0V

1.5V

1.5V

f = 1MHz: tr ≤ 10ns: tf ≤ 10ns

tZL

tLZ

2.3V

OUTPUT NORMALLY LOW

tZH

tHZ

OUTPUT NORMALLY HIGH

2.3V

Figure 7. Receiver Enable and Disable

0.5V

0.5V

1324 F07

APPLICATIONS INFORMATION

Thermal Shutdown Protection

The LTC1324 includes a thermal shutdown circuit which

protects against prolonged shorts at the driver outputs.

If a driver output is shorted to another output, ground or

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

a maximum of 250mA. When the die temperature rises

above 150°C, the thermal shutdown circuit turns off the

driver outputs. When the die cools to about 130°C, the

outputs turn on. 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.

Power Shutdown

The power shutdown feature of the LTC1324 is designed

for battery-powered systems. When SHDN is forced high,

the part enters shutdown mode. In shutdown, the supply

current typically drops from 1mA to 1μA and the driver

and receiver outputs are three-stated.

capacitor T network between each driver, receiver and the

connector. Unfortunately, the resistors will attenuate the

driver’s output signal applied to the cable. Because the

LTC1324 uses a single 5V supply, the resistors’ values

should be reduced to 5.1Ω to ensure enough voltage swing

on the cable (Figure 8). Another way to get maximum swing

and EMI immunity is to use a ferrite bead and capacitor as

the T network (Figure 9). For data rates below 250kbps,

the LTC1324 features a low EMI mode which limits the

rise time of the drivers to 400ns. With a lower rise time,

the EMI network can be eliminated, allowing more signal

voltage to reach the cable. Figures 10 and 11 show the

output signals of the driver with different slew rates.

TXD+

TXD

TXD–

5.1Ω

5.1Ω

5.1Ω

100pF

5.1Ω

100pF

120Ω

1324 F08

Figure 8

Supply Bypassing

The LTC1324 requires VCC be bypassed to prevent data

errors. A 1μF capacitor from VCC to ground is adequate.

EMI Filters and Slew Rate Control

Most LocalTalk applications need to use an electromag-

netic interference (EMI) filter consisting of a resistor-

FERRITE BEAD

FERRITE BEAD

100pF

Figure 9

1324 F09

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

1324fa

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