6

LTC1688/LTC1689

The LTC1688/LTC1689 family of RS485 quad differential

drivers employs a novel architecture and fabrication pro-

cess that allows ultra high speed operation (100Mbps)

and Hot Swap capability while maintaining the ruggedness

of RS485 operation (three-state outputs can float from

– 7V to 12V with a single 5V supply). Unlike typical CMOS

drivers whose propagation delay can vary as much as

500%, the propagation delay of the LTC1688/LTC1689

drivers will only vary by

±50% (a narrow ±4ns window).

This performance is achieved by designing the input stage

of each driver to have minimum propagation delay shift

over temperature and from part to part.

The LTC1688/LTC1689 have an ESD rating of 6kV human

body model.

50Mbps with 3V Operation

The LTC1688/LTC1689 are designed to operate with a 3V

power supply and still achieve 50Mbps operation (see

Electrical Characteristics table for 3V DC and AC specifica-

1688/89 F04

B

A

DI

3V

0V

1.5V

1.5V

90%

10%

90%

10%

Figure 4. Driver Propagation Delays

1688/89 F05

A, B

EN

3V

0V

1.5V

1.5V

5V

OUTPUT NORMALLY LOW

0.5V

A, B

0V

OUTPUT NORMALLY HIGH

0.5V

Figure 5. Driver Enable and Disable Times

SWITCHI G TI E WAVEFOR S

Figure 6. 3V High Speed Data Transmission

20ns/DIV

2V/DIV

2V/DIV

5V/DIV

1688/89 F06

LTC1689 OUTPUT

RECEIVER OUTPUT

FAR END OF CABLE

tions). Figure 6 shows waveforms of an LTC1689 driving

a receiver using 100 feet of Category 5 UTP. Both parts are

operating at 3V supply.