LT1332 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LT1332
Linear Technology
'LT1332' PDF : 8 Pages View PDF
LT1332
PI FU CTIO S
capacitors work well in this application. When V– is
powered from an external supply, the filter capacitor can
be considerably smaller (C ≥ 0.1µF). Ceramic capacitors
work well under these conditions. V– should be greater
than –13.2V and less than – 6.5V.
C–: Commutating Capacitor Input. When the LT1332 is
used with a switching regulator, a charge pump capacitor
should be connected from the regulator’s switch pin to the
C– pin. Make the external capacitor 1µF or larger with low
effective series resistance to maintain good charge pump
efficiency. Low ESR tantalum capacitors (ESR < 2Ω) work
well in this application. The C– pin should be left open
when V– is powered from an external supply.
DRIVER IN: RS232 Driver Input Pins. Inputs are TTL/
CMOS compatible, with threshold set to 1.2V. Unused
inputs should not float; tie them to VCC.
DRIVER OUT: Driver Outputs at RS232 Voltage Levels.
Outputs are in a high impedance state when in SHUT-
DOWN mode, or VCC = 0V. Outputs are fully short-circuit
protected from V– + 30V to V+ – 30V with the power on,
off or SHUTDOWN. Typical breakdowns are ±45V.
Applying higher voltages will not damage the device if
the overdrive is moderately current limited. Although
the outputs are protected, 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 (±5V to ±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. The re-
ceiver thresholds are specified at VCC = 3V. When VCC
varies from 2V to 6V, the lower threshold increases
about 3V. Regardless of these shifts, the device provides
accurate data from valid RS232 input signals. A graph in
the performance characteristics section shows typical
changes in the thresholds. The active receiver (RXA, Pin
10, S Package) remains functional in SHUTDOWN.
RX OUT: Receiver Outputs with TTL/CMOS Voltage Lev-
els. Outputs are in a high impedance stage when in
SHUTDOWN mode to allow data line sharing. Outputs are
fully short-circuit protected to ground or VCC with the
power on, off or in SHUTDOWN mode. The active receiver
(RXA, Pin 15, S Package) remains functional in SHUT-
DOWN.
U
ESD PROTECTIO
The RS232 line inputs of the LT1332 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
LT1332 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 applications 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 VCC,
V +, V – and GND shorted to ground or connected with low
ESR capacitors.
ESD Test Circuit
V+ 1
12V
0.1µF
C– 2
3
DRIVER OUT
4
RX IN
5
DRIVER OUT
RS232
LINE PINS
PROTECTED
TO ±10kV
6
RX IN
7
RX IN
8
RX IN
9
DRIVER OUT
10
RXA IN
11
NC
3V VCC 12
3V
0.1µF
24 V–
23 GND
LT1332
22 DRIVER IN
21 RX OUT
20 DRIVER IN
19 RX OUT
18 RX OUT
17 RX OUT
16 DRIVER IN
15 RXA OUT
14 RS232 ON/OFF
13
GND
LT1332 • TC
–12V
0.1µF
6
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