8

LTC1518/LTC1519

When the inputs are accidentally shorted (by cutting

through a cable, for example), the short-circuit fail-safe

feature will guarantee a high output logic level. Note also

that if the line driver is removed and the termination

resistors are left in place, the receiver will see this as a

“short” and output a logic high.

Both of these fail-safe features will keep the receiver from

outputting false data pulses under fault conditions.

Single-Ended Applications

Over short distances, the LTC1518/LTC1519 can be

configured to receive single-ended data by tying one

input to a fixed bias voltage and connecting the other

input to the driver output. In such applications, standard

high speed CMOS logic may be used as a driver for the

LTC1518/LTC1519. With a 22k minimum input resis-

tance, the receiver trip points may be easily adjusted to

accommodate different driver output swings by chang-

ing the resistor divider at the fixed input. Figure 6a shows

a single-ended receiver configuration with the driver and

receiver connected via PC traces. Note that at very high

speeds, transmission line and driver ringing effects must

be considered. Motorola’s

MECL System Design Hand-

book serves as an excellent reference for transmission

line and termination effects. To mitigate transmission

errors and duty cycle distortion due to driver ringing, a

small output filter or a dampening resistor on the driver’s

circuit voltage of 3.3V at both inputs, the receivers can be

used without an external bias applied to the fixed inputs.

The fixed input should be bypassed with a 0.01

µF ce-

ramic capacitor. The positive input should be driven with

a 5V CMOS part in order to minimize the skew caused by

the 3.3V threshold. Figure 6c shows this configuration.

Figure 6a. Single-Ended Receiver

Figure 6b. Techniques to Minimize Driver Ringing

Figure 6c. Self Biased Single Ended Receiver

–

+

2.2k

5V

PC TRACE

1/4

LTC1518

LTC1519

MC74ACT04

(TTL INPUT)

MC74AC04

(CMOS INPUT)

2.2k

1518/19 F06a

0.01

µF

10

Ω

PC TRACE

OR

PC TRACE

0.01

µF

MC74AC04

1518/19 F06b

10pF

10

Ω

–

+

PC TRACE

1/4

LTC1518

LTC1519

MC74ACT04

(TTL INPUT)

MC74AC04

(CMOS INPUT)

1518/19 F06c

0.01

µF

APPLICATIO S I FOR ATIO