Datasheet

6
LTC1688/LTC1689
16889fa
APPLICATIONS INFORMATION
WUU
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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
1688/89 F04
B
A
DI
V
O
V
O
–V
O
1/2 V
O
3V
0V
t
SKEW
1.5V
t
PLH
1.5V
t
PHL
1/2 V
O
V
DIFF
= V(A) – V(B)
90%
10%
t
f
90%
10%
t
SKEW
t
r
f = 1MHz; t
r
< 3ns; t
f
< 3ns
Figure 4. Driver Propagation Delays
1688/89 F05
A, B
EN
3V
0V
f = 1MHz; t
r
≤ 3ns; t
f
≤ 3ns
V
OL
V
OH
1.5V 1.5V
5V
OUTPUT NORMALLY LOW
t
ZL
1/2 V
DD
1/2 V
DD
t
LZ
0.5V
A, B
0V
t
ZH
OUTPUT NORMALLY HIGH
t
HZ
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
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.