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LT1280A

Low Power 5V RS232 Dual Driver/Receiver with 0.1µF Capacitors

Linear Technology 

TYPICAL PERFOR A CE CHARACTERISTICS

LT1280A/LT1281A

DRIVER 1

OUTPUT

Shutdown to Driver Outputs

10V

5V

GND

GND

DRIVER 2 – 5V

OUTPUT

– 10V

ON/OFF PIN

LT1280A • TPC12

Driver Output Waveforms

DRIVER OUTPUT

RL = 3k

CL = 2500pF

DRIVER OUTPUT

RL = 3k

INPUT

LT1280A • TPC13

PI FU CTIO S

VCC: 5V Input Supply Pin. This pin should be decoupled

with a 0.1µF ceramic capacitor close to the package pin.

Insufficient supply bypassing can result in low output

drive levels and erratic charge pump operation.

GND: Ground Pin.

ON/OFF: A TTL/CMOS Compatible Operating Mode Con-

trol. A logic low puts the LT1280A in shutdown mode.

Supply current drops to zero and both driver and receiver

outputs assume a high impedance state. A logic high fully

enables the device.

V+: Positive Supply Output (RS232 Drivers). V+ ≈ 2VCC –

1.5V. This pin requires an external charge storage capaci-

tor C ≥ 0.1µF, tied to ground or VCC. Larger value capaci-

tors may be used to reduce supply ripple. With multiple

transceivers, the V+ and V – pins may be paralleled into

common capacitors.

V–: Negative Supply Output (RS232 Drivers). V – ≈ –

(2VCC – 2.5V). This pin requires an external charge storage

capacitor C ≥ 0.1µF. Larger value capacitors may be used

to reduce supply ripple. With multiple transceivers, the V+

and V – pins may be paralleled into common capacitors.

TR1 IN, TR2 IN: RS232 Driver Input Pins. These inputs are

TTL/CMOS compatible. Inputs should not be allowed to

float. Tie unused inputs to VCC.

TR1 OUT, TR2 OUT: Driver Outputs at RS232 Voltage

Levels. Driver output swing meets RS232 levels for loads

up to 3k. Slew rates are controlled for lightly loaded lines.

Output current capability is sufficient for load conditions

up to 2500pF. Outputs are in a high impedance state when

in shutdown mode or VCC = 0V. Outputs are fully short-

circuit protected from V – + 30V to V + – 30V. Applying

higher voltages will not damage the device if the overdrive

is moderately current limited. Short circuits on one

output can load the power supply generator and may

disrupt the signal levels of the other outputs. The driver

outputs are protected against ESD to ±10kV for human

body model discharges.

REC1 IN, REC2 IN: Receiver Inputs. These pins accept

RS232 level signals (±30V) into a protected 5k terminat-

ing resistor. The receiver inputs are protected against ESD

to ±10kV for human body model discharges. Each receiver

provides 0.4V of hysteresis for noise immunity. Open

receiver inputs assume a logic low state.

REC1 OUT, REC2 OUT: Receiver outputs with TTL/CMOS

Voltage Levels. Outputs are in a high impedance state

when in shutdown mode to allow data line sharing. Out-

puts are fully short-circuit protected to ground or VCC with

the power ON, OFF or in the shutdown mode.

C1+, C1–, C2 +, C2 –: Commutating Capacitor Inputs.

These pins require two external capacitors C ≥ 0.1µF: one

from C1+ to C1– and another from C2+ to C2 –. C1 should

be deleted if a separate 12V supply is available and

connected to pin C1+. Similarly, C2 should be deleted if a

separate – 12V supply is connected to pin V –.

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