LT1039A Datasheet, PDF (7/12 Pages) Linear Technology – Triple RS232 Driver/Receiver with Shutdown

LT1039A/LT1039A-16
APPLICATIONS INFORMATION
When driving CMOS logic from a receiver that will be used
in the shutdown mode and there is no other active receiver
on the line, a 51k resistor can be placed from the logic input
to V_CC to force a definite logic level when the receiver
output is in a high impedance state.
Driving CMOS Logic from a Receiver
V_CC
RS232
INPUT
ON/OFF
INPUT
LT1039A
RECEIVER
51k* ^CMOS
LOGIC
LOGIC
OUTPUT
*FORCES LOGIC INPUT STATE
WHEN V_ON/OFF IS LOW
1039A AI06
To protect against receiver input overloads in excess of
±30V, a voltage clamp can be placed on the data line and
still maintain RS232 compatibility.
Driver inputs should not be allowed to float. Any unused
inputs should be tied to V_CC.
The BIAS pin is used to “keep alive” one receiver while in
the shutdown mode (all other circuitry being inactive).
This allows a system to be in shutdown and still have one
active receiver for transferring data.
Keeping Alive One Receiver While in Shutdown
LOGIC
SHUTDOWN
INPUT
25k
2 BIAS
17
ON/OFF
RS232 3
INPUT
16 LOGIC
OUTPUT
LT1039A
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Input Overvoltage Protection
1k
RS232
INPUT
30V
5.6k
30V
RECEIVER
30k
LOGIC
OUTPUT
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The receiver input impedance of the LT1039A is nominally
30kΩ. For applications requiring a 5kΩ input impedance,
a 5.6k resistor can be connected from the receiver input to
ground.
5kΩ Impedance Matching
RS232
INPUT
5.6k
RECEIVER
30k
LOGIC
OUTPUT
It can also be used to make an RS232 compatible shut-
down control line. Driving the BIAS pin low through a
resistance of 24k to 30k keeps the receiver active. Do not
drive the BIAS pin directly from a logic output without the
series resistor. An unused BIAS pin should be left open.
RS232 Compatible Shutdown Control Line
25k
RS232
SHUTDOWN
INPUT
2 BIAS
3
17
ON/OFF
16
LT1039A
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