LTC1480 Linear Technology, LTC1480 Datasheet - Page 6

• Manufacturer Part Number: LTC1480
• Description: 3.3V Ultra-Low Power RS485 Transceiver
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
SWITCHI G TI E WAVEFOR S
LTC1480
6
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
A – B
A, B
A, B
RO
RO
RO
DE
RE
–V
V
3.3V
3.3V
V
V
V
V
V
OD2
OD2
V
3V
0V
OH
0V
OH
OL
3V
0V
OH
0V
OL
OL
U
U U
W
W
Figure 8. Receiver Enable and Disable Times
t
Figure 6. Driver Enable and Disable Times
PHL
Figure 7. Receiver Propagation Delays
1.5V
1.5V
W
0V
U
2.3V
2.3V
1.5V
1.5V
1.5V
t
t
t
t
ZL(SHDN)
ZH(SHDN)
ZL(SHDN)
ZH(SHDN)
f = 1MHz, t
f = 1MHz, t
f = 1MHz, t
OUTPUT NORMALLY HIGH
OUTPUT NORMALLY HIGH
OUTPUT NORMALLY LOW
OUTPUT NORMALLY LOW
, t
, t
, t
, t
ZL
ZH
ZL
ZH
r
r
r
LOGIC
10ns, t
OUTPUT
10ns, t
Figure 9. Conventional
10ns, t
INPUT
CMOS Output Stage
f
f
f
10ns
10ns
10ns
P1
N1
t
t
t
t
V
HZ
LZ
LZ
HZ
t
CC
PLH
LTC1480 • F10
1.5V
1.5V
OUTPUT
0.5V
0.5V
0.5V
0.5V
D1
D2
0V
1.5V
LOGIC
LTC1480 Output Stage
LTC1480 • F06
LTC1480 • F07
LTC1480 • F08
Figure 10.
N1
P1
V
CC
SD4
SD3
LTC1480 • F09
OUTPUT
D1
D2