6
LT1341
PI FU CTIO S
U
UU
V
–
: Negative Supply Output (RS232 Drivers). V
–
≈
–(2V
CC
– 2.5V). This pin requires an external charge
storage capacitor C ≥ 0.1µF. To reduce supply ripple,
increase the size of the storage capacitor. With multiple
transceivers, the V
+
and V
–
pins may be paralleled into
common filter capacitors.
C1
+
, C1
–
, C2
+
, C2
–
: Commutating Capacitor Inputs. These
pins require two external capacitors C ≥ 0.2µF: one from
C1
+
to C1
–
, and another from C2
+
to C2
–
. The capacitor’s
effective series resistance should be less than 2Ω. For
C ≥ 1µF, low ESR tantalum capacitors work well in this
application, although small value ceramic capacitors may
be used with a minimal reduction in charge pump compli-
ance. When a 12V supply is available, C1 may be omitted.
Connect the 12V supply to C1
+
and V
+
. The 12V supply
should be decoupled with a 0.1µF ceramic capacitor.
DRIVER IN: RS232 Driver Input Pins. These inputs are
TTL/CMOS compatible. Tie unused inputs to V
CC
.
DRIVER OUT:
Driver Outputs at RS232 Voltage Levels.
Outputs are in a high impedance state when in
shut-
down
mode, V
CC
= 0V, or when the DRIVER DISABLE
pin is active. Outputs are fully short-circuit protected
from V
OUT
= V
–
+ 30V to V
OUT
= V
+
– 30V. Applying
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 ±10kV 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.
RX OUT: Receiver Outputs with TTL/CMOS Voltage Lev-
els. Outputs are in a high impedance state when in shut-
down mode to allow data line sharing. Outputs, including
LOW-Q RX OUT, are fully short-circuit protected to ground
or V
CC
with the power on, off, or in shutdown mode.
LOW Q-CURRENT RX IN: Low Power Receiver Input. This
special receiver remains active when the part is in shut-
down mode, consuming typically 60µA. This receiver has
the same input and protection characteristics as the other
receivers.
LOW Q-CURRENT RX OUT: Low Power Receiver Output.
This pin produces the same TTL/CMOS output voltage
levels with slightly decreased speed and short-circuit
current.
ESD PROTECTIO
U
The RS232 line inputs of the LT1341 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
LT1341 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
CC
,
V
+
, V
–
and GND shorted to ground or connected with low
ESR capacitors.
ESD Test Circuit
LT1341 • ESD TC
5V V
CC
0.1µF
0.2µF
0.1µF
RS232
LINE PINS
PROTECTED
TO ±10kV
LT1341
1
2
3
4
5
6
7
8
9
10
11
12
13
14
DRIVER 1 OUT
RX1 IN
DRIVER 2 OUT
RX2 IN
RX3 IN
RX4 IN
DRIVER 3 OUT
RX5 IN (LOW-Q)
ON/OFF
NC
28
27
26
25
24
23
22
21
20
19
18
17
16
15
0.2µF
DRIVER 1 IN
RX1 OUT
DRIVER 2 IN
RX2 OUT
RX3 OUT
RX4 OUT
DRIVER 3 IN
RX5 OUT (LOW-Q)
V
–
V
+
0.1µF
GND
DRIVER DISABLE
NC
