7

LT1780/LT1781

ESD PROTECTIO

The RS232 line inputs of the LT1780/LT1781 have on-chip

protection from ESD transients up to

±15kV air gap and

±8kV contact tested to IEC-1000-4-2 test methods. 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 circuit must be connected to ground through low

impedances. The power supply decoupling capacitors and

charge pump storage capacitors provide this low imped-

ance in normal application of the circuit. The only con-

straint is that low ESR capacitors must be used for

bypassing and charge storage. ESD testing must be done

connected with low ESR capacitors.

Operation Using 5V and 12V Power Supplies

1780 • ESD TC

0.1

µF

RS232

LINE PINS

PROTECTED

TO IEC-1000-4-2

LEVEL 4

1

2

3

4

5

6

7

8

9

18

17

16

15

14

13

12

11

10

0.1

µF

0.1

µF

0.1

µF

NC

DR2 OUT

LT1780

0.1

µF

ON/OFF

GND

DR1 OUT

RX1 IN

RX1 OUT

DR1 IN

DR2 IN

RS232

LINE PINS

PROTECTED

TO IEC-1000-4-2

LEVEL 4

RX2 IN

RX2 OUT

ESD Test Circuit

5k

5k

0.1

µF

0.1

µF

LOGIC

INPUTS

LOGIC

OUTPUTS

ON/OFF

18

10

13

11

12

6

5

4

2

16

9

14

8

15

7

3

17

5V INPUT

RS232 OUTPUT

RS232 OUTPUT

RS232 INPUT

RS232 INPUT

1780/81 • TA03

LT1780

12V INPUT

TYPICAL APPLICATIO