10

LTC1518/LTC1519

Figure 9 shows a trace with 100ft category 5 UTP between

an LTC1685 driver and an LTC1518 receiver. Notice that at

the far end of the cable, the signal to the LTC1518 input has

been reduced. Figure 10 shows a 52Mbps square wave.

Output Short-Circuit Protection

The LTC1518/LTC1519 employ voltage sensing short-

circuit protection at the output terminals. For a given input

differential, this circuitry determines what the correct

output level should be. For example, if the input differential

is

≥ 300mV, it expects the output to be a logic high. If the

output is subsequently shorted to a voltage below VDD/2,

this circuitry shuts off the output devices and turns on a

smaller device in its place. A timeout period of about 50ns

is used in order to maintain normal high frequency opera-

tion, even under heavy capacitive loads (>100mA tran-

sient current into the load).

Figure 9. 20ns Pulse Propagating Down 100ft of Category 5 UTP

Figure 10. 52Mbps Pulse Train Over 100ft of Category 5 UTP

50ns/DIV

LTC1518/19 • F09

2V/DIV

2V/DIV

5V/DIV

DRIVER

INPUT

RECEIVER

INPUT

RECEIVER

OUTPUT

CABLE

DELAY

NOTES:

TOP TRACE: LTC1685 DRIVER INPUT

MID TRACE: LTC1518 INPUT AT FAR END

OF 100ft CATAGORY 5 UTP

BOTTOM TRACE: LTC1518 OUTPUT

20ns/DIV

LTC1518/19 • F10

1V/DIV

5V/DIV

RECEIVER

INPUT

RECEIVER

OUTPUT

NOTES:

TOP TRACE: LTC1518 INPUT AT FAR END

OF 100ft CAT 5 UTP

BOTTOM TRACE: LTC1518 OUTPUT