LTC1688/LTC1689
SWITCHI G TI E WAVEFOR S
3V
DI
0V
t
PLH
B
V
O
A
1/2 V
O
V
O
– V
O
10%
t
r
90%
t
SKEW
V
DIFF
= V(A) – V(B)
1/2 V
O
t
SKEW
90%
10%
t
f
1688/89 F04
1.5V
Figure 4. Driver Propagation Delays
3V
EN
0V
t
ZL
5V
A, B
V
OL
V
OH
A, B
0V
t
ZH
1/2 V
DD
1.5V
1/2 V
DD
Figure 5. Driver Enable and Disable Times
APPLICATIONS INFORMATION
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-
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.
6
U
W
W
U
W
U
U
f = 1MHz; t
r
< 3ns; t
f
< 3ns
1.5V
t
PHL
f = 1MHz; t
r
≤
3ns; t
f
≤
3ns
1.5V
t
LZ
OUTPUT NORMALLY LOW
0.5V
OUTPUT NORMALLY HIGH
t
HZ
0.5V
1688/89 F05
LTC1689 OUTPUT
2V/DIV
FAR END OF CABLE
2V/DIV
RECEIVER OUTPUT
5V/DIV
20ns/DIV
1688/89 F06
Figure 6. 3V High Speed Data Transmission
16889fa
LINEAR_DIMENSIONS [ LINEAR DIMENSIONS SEMICONDUCTOR ]
