Datasheet

LT1785/LT1785A/
LT1791/LT1791A
11
178591fc
APPLICATIONS INFORMATION
Slew Limiting for EMI Emissions Control
The LT1785/LT1791 feature controlled driver output slew
rates to control high frequency EMI emissions from equip-
ment and data cables. The slew limiting limits data rate
operation to 250kbaud. Slew limiting also mitigates the
adverse affects of imperfect transmission line termina-
tion caused by stubs or mismatched cable. In some low
speed, short distance networks, cable termination may
be eliminated completely with no adverse effect on data
transmission.
Data Network Cable Selection and Termination
Long distance data networks operating at high data trans-
mission rates should use high quality, low attenuation
cable with well-matched cable terminations. Short distance
networks at low data rates may use much less expensive
PVC cable. These cables have characteristic impedances
as low as 72Ω. The LT1785/LT1791 output drivers are
guaranteed to drive cables as low as 72.
Figure 9. Full-Duplex RS422
5
4
3
2
A
B
Z
Y
12
11
10
9
RO
RE
DE
DI
178591 F09
TX
120Ω
5
4
3
2
Y
Z
B
A
9
10
11
12
RO
LT1791LT1791
RE
DE
DI
RX
TX
120Ω
RX