6

LT1332

PI FU CTIO S

powered from an external supply, the filter capacitor can

be considerably smaller (C

≥ 0.1µF). Ceramic capacitors

than –13.2V and less than – 6.5V.

used with a switching regulator, a charge pump capacitor

should be connected from the regulator’s switch pin to the

µF or larger with low

effective series resistance to maintain good charge pump

efficiency. Low ESR tantalum capacitors (ESR < 2

Ω) work

DRIVER IN: RS232 Driver Input Pins. Inputs are TTL/

CMOS compatible, with threshold set to 1.2V. Unused

DRIVER OUT: Driver Outputs at RS232 Voltage Levels.

Outputs are in a high impedance state when in SHUT-

off or SHUTDOWN. Typical breakdowns are

±45V.

Applying higher voltages will not damage the device if

the overdrive is moderately current limited. Although

the outputs are protected, 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.

RX IN: Receiver Inputs. These pins accept RS232 level

signals (

±5V to ±30V) into a protected 5k terminating

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. The re-

varies from 2V to 6V, the lower threshold increases

about 3V. Regardless of these shifts, the device provides

accurate data from valid RS232 input signals. A graph in

the performance characteristics section shows typical

changes in the thresholds. The active receiver (RXA, Pin

10, S Package) remains functional in SHUTDOWN.

RX OUT: Receiver Outputs with TTL/CMOS Voltage Lev-

els. Outputs are in a high impedance stage when in

SHUTDOWN mode to allow data line sharing. Outputs are

power on, off or in SHUTDOWN mode. The active receiver

(RXA, Pin 15, S Package) remains functional in SHUT-

DOWN.

ESD PROTECTIO

ESD Test Circuit

The RS232 line inputs of the LT1332 have on-chip protec-

tion from ESD transients up to

±10kV. The protection

structures act to divert the static discharge safely to

system ground. In order for the ESD protection to function

effectively, the power supply and ground pins of the

LT1332 must be connected to ground through low imped-

ances. The power supply decoupling capacitors and charge

pump storage capacitors provide this low impedance in

normal applications of the circuit. The only constraint is

that low ESR capacitors must be used for bypassing and

ESR capacitors.

LT1332 • TC

LT1332

1

2

3

4

5

6

7

8

9

10

11

12

24

23

22

21

20

19

18

17

16

15

14

13

–12V

0.1

µF

0.1

µF

3V

RS232

LINE PINS

PROTECTED

TO ±10kV

DRIVER OUT

RX IN

DRIVER OUT

RX IN

RX IN

RX IN

DRIVER OUT

RXA IN

NC

GND

GND

DRIVER IN

RX OUT

DRIVER IN

RX OUT

RX OUT

RX OUT

DRIVER IN

RXA OUT

RS232 ON/OFF

0.1

µF

12V