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 con-

figured 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 resistance, the

receiver trip points may be easily adjusted to accommo-

date different driver output swings by changing the resis-

tor 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 con-

sidered. Motorola’s

MECL System Design Handbook serves

as an excellent reference for transmission line and termi-

nation effects. To mitigate transmission errors and duty

cycle distortion due to driver ringing, a small output filter

as shown in Figure 6b. With an open 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 ceramic capacitor. The

positive input should be driven with a 5V CMOS pat in

order to minimize the skew caused by the 3.3V threshold.

Figure 6c shows this configuration. Note that due to the

–

+

2.2k

5V

PC TRACE

1/4

LTC1518

LTC1519

MC74ACT04

(TTL INPUT)

MC74AC04

(CMOS INPUT)

2.2k

1518/19 F06a

0.01

µF

Figure 6a. Single-Ended Receiver

Figure 6b. Techniques to Minimize Driver Ringing

10

Ω

PC TRACE

OR

PC TRACE

0.01

µF

MC74AC04

1518/19 F06b

10pF

10

Ω

Figure 6c. Self Biased Single Ended Receiver

–

+

PC TRACE

1/4

LTC1518

LTC1519

MC74ACT04

(TTL INPUT)

MC74AC04

(CMOS INPUT)

1518/19 F06c

0.01

µF