LT1342 Linear Technology, LT1342 Datasheet - Page 6

• Manufacturer Part Number: LT1342
• Description: 5V RS232 Transceiver with 3V Logic Interface
• Manufacturer: Linear Technology

PI FU CTIO S
LT1342
V
–(2V
storage capacitor C
increase the size of the storage capacitor.
C1
pins require two external capacitors C 0.2 F: one from
C1
effective series resistance should be less than 2 . For
C
application, although small value ceramic capacitors may
be used with a minimal reduction in charge pump compli-
ance. For operation with an external 12V supply, omit C1
and connect the 12V supply to pin C1
shorted to C1
supply must be bypassed with a 0.1F capacitor.
DRIVER IN: RS232 Driver Input Pins. These inputs are
compatible with TTL or CMOS logic. Tie unused inputs to
V
DRIVER OUT: Driver Outputs at RS232 Voltage Levels.
Driver output swing meets RS232 levels for loads up to
3k. Slew rates are controlled for lightly loaded lines.
Output current capability is sufficient for load condi-
tions up to 2500pF. Outputs are in a high impedance
ESD PROTECTIO
The RS232 line inputs of the LT1342 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
LT1342 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 application of the circuit. The only constraint is that
low ESR capacitors must be used for bypassing and
charge storage. ESD testing must be done with pins V
V
ESR capacitors.
6
CC
–
+
, V
: Negative Supply Output (RS232 Drivers). V
+
+
U
, C1
to C1
or V
1 F, low ESR tantalum capacitors work well in this
CC
–
and GND shorted to ground or connected with low
–
– 2.5V). This pin requires an external charge
L
, C2
–
.
U
, and another from C2
+
, C2
+
when a separate supply is used. The 12V
–
: Commutating Capacitor Inputs. These
U
0.1 F. To reduce supply ripple,
U
+
to C2
+
. Pin V
–
. The capacitor’s
+
may also be
–
CC
,
state when in shutdown mode, V
DRIVER DISABLE pin is active. Outputs are fully short-
circuit protected from V
higher voltages will not damage the device if the over-
drive is moderately current limited. 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 10V for
human body model discharges.
RX IN: Receiver Inputs. These pins accept RS232 level
signals ( 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. Open receiver
inputs assume a logic low state.
RX OUT: Receiver Outputs with 3.3V Logic Compatible
Voltage Levels. Outputs are in a high impedance state
when in shutdown mode to allow data line sharing.
Outputs are fully short-circuit protected to ground or V
or V
Receiver output level is determined by V
Use V
interfacing with 5V logic.
PROTECTED
0.1 F
LINE PINS
TO 10kV
RS232
L
L
with the power on, off, or in shutdown mode.
= 3.3V for interfacing with 3.3V logic, V
DRIVER 1 OUT
DRIVER 2 OUT
DRIVER 3 OUT
0.1 F
0.2 F
ON/OFF
RX1 IN
RX2 IN
RX3 IN
RX4 IN
RX5 IN
5V V
3V V
V
CC
L
+
10
11
12
13
14
1
2
3
4
5
6
7
8
9
0.1 F
–
ESD Test Circuit
+ 30V to V
LT1342
CC
= 0V, or when the
+
L
– 30V. Applying
28
27
26
25
24
23
22
21
20
19
18
17
16
15
supply voltage.
DRIVER 1 IN
RX1 OUT
DRIVER 2 IN
RX2 OUT
RX3 OUT
RX4 OUT
DRIVER 3 IN
RX5 OUT
V
GND
DRIVER DISABLE
NC
–
L
= 5V for
0.1 F
0.2 F
LT1342 • ESD TC
CC