LT1080/LT1081
U
U
U
PI FU CTIO S (Pin numbers refer to LT1080)
C1+; C1–; C2+; C2– (Pins 2, 4, 5, 6): Requires an external
capacitor (≥1µF) from C1+ to C1– and another from C2+
to C2–. Pin 2 can be used for connecting a second positive
supply.Whenaseparatepositivesupplyisused,C1canbe
deleted.
voltages will not damage the device if moderately current
limited. Shorting one output will affect output from the
other.
REC2 IN; REC1 IN (Pins 9, 14): Receiver Inputs. Accepts
RS232 voltage levels (±30V) and has 0.4V of hysteresis to
provide noise immunity. Input impedance is nominally
5kΩ.
V+ (Pin 3): Positive Supply for RS232 Drivers.
V+ ≈ 2VCC – 1.5V. Requires an exterenal capacitor (≥1µF)
for charge storage. May be loaded (up to 15mA) for
external system use. Loading does reduce V+ voltage (see
graphs). Capacitor may be tied to ground or +5V input
supply.Withmultipletransceivers,theV+ andV– pinsmay
be paralleled into common capacitors.
REC2 OUT; REC1 OUT (Pins 10, 13): Receiver Outputs
with TTL/CMOS Voltage Levels. Outputs are in a high
impedance state when in the SHUTDOWN mode to allow
data line sharing. Outputs are fully short-circuit protected
to ground or VCC with power on, off or in the SHUTDOWN
mode.
V– (Pin 7): Negative Supply for RS232 Drivers.
V– ≈ –(2VCC – 2.5V). Requires an external capacitor
(≥1µF) for charge stroage. May be loaded (up to –15mA)
for external system use. Loading does reduce V– voltage
(see graphs). With multiple transceivers, the V+ and V–
pins may be paralleled into common capacitors.
TR2 IN; TR1 IN (Pins 11, 12): RS232 Driver Input Pins.
Inputs are TTL/CMOS compatible. Inputs should not be
allowed to float. Tie unused inputs to VCC.
GND (Pin 16): Ground Pin.
VCC (Pin 17): Input Supply Pin. Supply current drops to
TR2 OUT; TR1 OUT (Pins 8, 15): Driver Outputs with
RS232 Voltage Levels. Outputs are in a high impedance
state when in the SHUTDOWN mode or when power is off
(VCC = 0V) to allow data line sharing. Outputs are fully
short-circuit protected from (V– + 30V) to (V+ – 30V) with
power on, off or in the SHUTDOWN mode. Typical output
breakdowns are greater than ±45V and higher applied
zero in the SHUTDOWN mode.
ON/OFF (Pin 18): Contols the operation mode of the
LT1080 and is TTL/CMOS compatible. A logic low puts the
device in the SHUTDOWN mode which reduces input
supply current to zero and places both driver and receiver
outputs in a high impedance state. A logic high fully
enables the device.
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Generation from VCC
or Shutdown
Driver Output Voltage
Supply Generator Outputs
10
8
10
8
10
8
+
+
V
= 5.5V
= 4.5V
OUTPUT HIGH
V
–
OUTPUT VOLTAGE
LOADED TO GROUND
CC
CC
V
SUPPLY
LOADED TO V
6
6
6
V
CC
= 5V
V
C1 TO C4 = 1µF
V
= 5V
4
CC
CC
4
4
+
–
R
= 4.7k; V TO V
L
2
2
2
0
R
= 3k
0
V
CC
= 5V
0
L
–2
–4
–6
–8
–10
–2
–4
–6
–8
–10
–2
–4
–6
–8
–10
V
= 5V
V
V
= 4.5V
= 5.5V
CC
LOADED TO GROUND
+
LOADED TO V
–
–
OUTPUT LOW
50 75 100 125
CC
V
SUPPLY
V
OUTPUT VOLTAGE
10 12 14 16 18 20
OUTPUT CURRENT (mA)
–55 –25
0
25
0
2
4
6
8
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
TIME (ms)
TEMPERATURE (°C)
1080/81 G01
1080/81 G02
1080/81 G03
4
Linear [ Linear ]
