
6
LTC1688/LTC1689
16889fa
APPLICATIONS INFORMATION
WU
U
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
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
1688/89 F04
B
A
DI
VO
–VO
1/2 VO
3V
0V
tSKEW
1.5V
tPLH
1.5V
tPHL
1/2 VO
VDIFF = V(A) – V(B)
90%
10%
tf
90%
10%
tSKEW
tr
f = 1MHz; tr < 3ns; tf < 3ns
Figure 4. Driver Propagation Delays
1688/89 F05
A, B
EN
3V
0V
f = 1MHz; tr ≤ 3ns; tf ≤ 3ns
VOL
VOH
1.5V
5V
OUTPUT NORMALLY LOW
tZL
1/2 VDD
tLZ
0.5V
A, B
0V
tZH
OUTPUT NORMALLY HIGH
tHZ
0.5V
Figure 5. Driver Enable and Disable Times
SWITCHI G TI E WAVEFOR S
UW
W
Figure 6. 3V High Speed Data Transmission
20ns/DIV
2V/DIV
5V/DIV
1688/89 F06
LTC1689 OUTPUT
RECEIVER OUTPUT
FAR END OF CABLE
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.