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LT1331

3V RS562 or 5V/3V RS232 Transceiver with One Receiver Active in Shutdown

Linear Technology 

LT1331

APPLICATI S I FOR ATIO

Power Saving Operational Modes

The LT1331 has both shutdown and driver disable oper-

ating modes. These operating modes can optimize power

consumption based upon applications needs.

The shutdown control turns off all circuitry except for

Low-Q RX5. RX5 operates entirely from the VL power

supply, so the power consumption from VCC drops to

zero. The VCC power supply may be turned off while in

shutdwon, which may allow greater power savings in

some systems. When RX5 detects a signal, this informa-

tion can be used to wake up the system for full operation.

If more than one line must be monitored, the driver

disable mode provides a power efficient operating

option. The driver disable mode turns off the charge

pumps and RS232 drivers, but keeps all five receivers

active. Power consumption in driver disable mode is 3mA

from VL and less than 100µA from VCC.

Mixed 5V/3V Operation

When operated with VCC = 5V and VL = 3.3V supplies, the

RS232 drivers meet or exceed all RS232 or V.28 commu-

nication interface standards. Data rates up to 120kbaud

are supported, and all standard RS232 compatible mice

may be driven by the LT1331.

3V Operation

VCC = 3.3V operation of the LT1331 results in lower driver

output swing than with VCC = 5V. The driver output swing,

when operated with VCC = 3.3V, is guaranteed to be at

least –2.7V to 3.7V, with typical swing being –3.3V to 4V.

This insures compatibility with all commonly used RS232

and RS562 interface circuits. Table 1 summarizes the

receiver input threshold specifications for RS232 circuits

from many manufacturers.

Table 1. Commonly Used RS232 Interface Circuit Receiver Thresholds

MANUFACTURER

PART NUMBER COMPATIBLE

INPUT LOW THRESHOLD

MIN

TYP

MAX

Linear Technology

LT1080



0.8

1.3

–

LT1137A



0.8

1.3

–

LT1330



0.8

1.3

–

LT1281



0.8

1.3

–

All Others



Texas Instruments

SN75189



0.65

1.0

1.25

SN75189A



0.65

1.0

1.25

MAX232



0.8

1.2

–

SN75C185



0.65

1.0

1.25

Maxim

MAX232A



0.8

1.3

–

Sipex

MAX241

SP232



0.6

1.2

–



0.8

1.2

–

SP301



0.75

–

1.35

Motorola

MC1489

MC1489A



0.75

–

1.25



0.75

0.8

1.25

National

DS1489



0.75

1.0

1.25

DS14C89A



0.5

–

1.9

INPUT HIGH THRESHOLD

MIN

TYP

MAX

–

1.7

2.4

–

1.7

2.4

–

1.7

2.4

–

1.7

2.4

0.9

1.3

1.6

1.55

1.9

2.25

–

1.7

2.4

1.6

2.1

2.55

–

1.8

2.4

–

1.5

2.4

–

1.7

2.4

1.75

–

2.5

1.0

–

1.5

1.75

1.95

2.25

1.0

1.25

1.5

1.3

–

2.7

6

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