6

LTC1480

SWITCHI G TI E WAVEFOR S

Figure 6. Driver Enable and Disable Times

1.5V

2.3V

2.3V

1.5V

0.5V

0.5V

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

3V

0V

DE

3.3V

0V

A, B

A, B

LTC1480 • F06

Figure 7. Receiver Propagation Delays

1.5V

RO

A – B

0V

0V

1.5V

OUTPUT

INPUT

LTC1480 • F07

Figure 8. Receiver Enable and Disable Times

1.5V

1.5V

1.5V

1.5V

0.5V

0.5V

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

3V

0V

RE

3.3V

0V

RO

RO

LTC1480 • F08

APPLICATIO S I FOR ATIO

CMOS Output Driver

The LTC1480 transceiver provides full RS485 compatibil-

ity while operating from a single 3.3V supply. The RS485

specification requires that a transceiver withstand com-

mon-mode voltages of up to 12V or –7V at the RS485 line

connections. Additionally, the transceiver must be im-

mune to both ESD and latch-up, This rules out traditional

CMOS drivers, which include parasitic diodes from their

driver outputs to each supply rail (Figure 9). The LTC1480

uses a proprietary process enhancement which adds a

pair of Schottky diodes to the output stage (Figure 10),

preventing current from flowing when the common-mode

LOGIC

P1

D1

OUTPUT

D2

N1

LTC1480 • F10

LOGIC

SD3

P1

D1

OUTPUT

SD4

D2

N1

LTC1480 • F09

Figure 9. Conventional

CMOS Output Stage

Figure 10.

LTC1480 Output Stage