LTC1688 Linear Technology, LTC1688 Datasheet - Page 6

• Manufacturer Part Number: LTC1688
• Description: 100Mbps RS485 Hot Swapable Quad Drivers
• Manufacturer: Linear Technology

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