Datasheet

7
LT1780/LT1781
ESD PROTECTIO
U
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
with pins V
CC
, V
L
, V
+
, V
–
, and GND shorted to ground or
connected with low ESR capacitors.
Operation Using 5V and 12V Power Supplies
1780 • ESD TC
0.1µF
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
0.1µF
0.1µF
0.1µF
NC
C1
+
V
+
C1
–
C2
+
C2
–
V
–
DR2 OUT
LT1780
0.1µF
ON/OFF
5V V
CC
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
0.1µF0.1µF
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
–12V
OUT
RS232 OUTPUT
RS232 OUTPUT
RS232 INPUT
RS232 INPUT
1780/81 • TA03
LT1780
12V INPUT
U
TYPICAL APPLICATIO