Datasheet

6
LT1280A/LT1281A
ESD PROTECTIO
U
The RS232 line inputs of the LT1280A/LT1281A have on-
chip protection 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 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.
ESD Test Circuit
1280A ESD TC
0.1µF
RS232
LINE PINS
PROTECTED
TO ±10kV
1
2
3
4
18
17
16
15
14
13
12
11
10
0.1µF
0.1µF
0.1µF
NC
C1
+
V
+
C1
C2
+
C2
V
DR2 OUT
LT1280A
0.1µF
ON/OFF
5V V
CC
GND
DR1 OUT
RX1 IN
RX1 OUT
DR1 IN
DR2 IN
RS232 
LINE PINS 
PROTECTED 
TO ±10kV
RX2 IN
RX2 OUT
+
+
+
+
+
5
6
7
8
9
U
A
O
PP
L
IC
AT
ITY
P
I
CA
L
Supporting an LT1039 (Triple Driver/Receiver)
30k
30k
RS232 OUTPUT
RS232 OUTPUT
RS232 INPUT
RS232 INPUT
LT1280A • TA04
LT1039
TTL INPUT
30k
RS232 INPUT
V
CC
TTL INPUT
TTL INPUT
TTL OUTPUT
TTL OUTPUT
TTL OUTPUT
ON/OFF
RS232 OUTPUT
5k
RS232 OUTPUT
RS232 INPUT
LT1280A
TTL INPUT
5k
RS232 INPUT
V
CC
TTL INPUT
TTL OUTPUT
TTL OUTPUT
ON/OFF
RS232 OUTPUT
1µF
2
4
1µF
5
6
3
7
18 17
1µF
1µF
GND
16
GND
10
V
+
V
1
9
18 17
5V
SHUTDOWN
C2
C2
+
C1
C1
+
V
+
V
11
12
13
10
15
14
9
8
12
14
16
11
13
15
7
5
3
8
6
4
+
+
+
+