LT1080_15 Datasheet, PDF (4/12 Pages) Linear Technology – Advanced Low Power 5V RS232 Dual Driver/Receiver

LT1080/LT1081
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. When a separate positive supply is used, C1 can be
deleted.
V⁺ (Pin 3): Positive Supply for RS232 Drivers.
V⁺ ≈ 2V_CC – 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. With multiple transceivers, the V⁺ and V^– pins may
be paralleled into common capacitors.
V^– (Pin 7): Negative Supply for RS232 Drivers.
V^– ≈ –(2V_CC – 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 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
(V_CC = 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
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.
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 V_CC with power on, off or in the SHUTDOWN
mode.
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 V_CC.
GND (Pin 16): Ground Pin.
V_CC (Pin 17): Input Supply Pin. Supply current drops to
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.
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Output Voltage
10
V_CC = 5.5V
8
OUTPUT HIGH
6
V_CC = 4.5V
4
V_CC = 5V
2
0 R_L = 3k
–2
–4 _{VCC = 4.5V}
–6
V_CC = 5V
–8
V_CC = 5.5V
–10
–55 –25 0
OUTPUT LOW
25 50 75 100 125
TEMPERATURE (°C)
1080/81 G01
4
Supply Generator Outputs
10
V⁺ OUTPUT VOLTAGE
8 _{LOADED TO V–}
6
LOADED TO GROUND
4
2
0 V_CC = 5V
–2
–4
–6 LOADED TO V⁺
LOADED TO GROUND
–8
V^– OUTPUT VOLTAGE
–10
0 2 4 6 8 10 12 14 16 18 20
OUTPUT CURRENT (mA)
1080/81 G02
Supply Generation from V_CC
or Shutdown
10
V⁺ SUPPLY
8
6
V_CC = 5V
4
C1 TO C4 = 1µF
R_L = 4.7k; V⁺ TO V^–
2
0
–2
–4
–6
–8
–10
0
V^– SUPPLY
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
TIME (ms)
1080/81 G03
10801fe