LT1332CSW Linear Technology, LT1332CSW Datasheet - Page 7

• Manufacturer Part Number: LT1332CSW
• Description: IC TXRX RS232 W/12V VPP 24-SOIC
• Manufacturer: Linear Technology
• Type: Transceiverr

Specifications of LT1332CSW

• Number Of Drivers/receivers: 3/5
• Protocol: RS232
• Voltage - Supply: 2 V ~ 6 V
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Operation with a Switching Regulator
The LT1332 is designed to be powered from an external
switching regulator which may be used elsewhere for power
conditioning. In a typical application, the LT1332 shares
the regulator’s positive output, while charge is capacitively
pumped from the regulator’s switch pin to the negative
supply. Schottky rectifiers built into the LT1332 simplify
the charge pump design. When used with a micropower
switcher like the LT1109A, the Burst Mode
the charge pump resembles the switching characteristics
of the LT1237 and similar devices.
The V
cross regulation and the regulator’s minimum duty cycle
to control V
that when the regulator operates at minimum duty cycle,
sufficient charge will transfer to the V
maintain a voltage of at least –6.5V.
While only 0.1µF ceramic decoupling capacitors are
needed on the positive supply inputs, low ESR tantalum
APPLICATIONS INFORMATION
ON/OFF
3V V
INPUT
–
supply is not directly regulated. The circuit relies on
CC
2.7V < V
I(V
V
IN
–
0.1µF
0.1µF
+
IN
) < 14mA (UNLOADED)
. Select the C
1µF
IN
< 5.5V
+
68 µF
V
C
3V V
SHUTDOWN
+
–
OPTIONAL
LT1332
CC
GND
ON/OFF
V
IN
LT1172
–
GND
GND
Figure 1. Multiple LT1332s Powered from a Single LT1172 DC/DC Converter
V
VN2222LL
and V
–
100µH
L1*
V
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
SW
FB
V
C
+
–
10µF
storage capacitors so
+
0.1µF
0.1µF
1k
1N5817
–
1µF
0.1µF
storage cap to
™
operation of
8V
135k**
25k**
22µF
V
C
3V V
+
–
LT1332
CC
+
ON/OFF
GND
GND
V
–
LT1332 • F01
**
+
*
L1 = SUMIDA CD105-101K OR COILCRAFT DO3316-104
1% METAL FILM
capacitors should be used in the charge pump to reduce
voltage losses. The C
and the V
a rule of thumb, make the V
times bigger than the C
regulator’s minimum duty cycle. Using large values for
the V
Multiple Transceivers
The circuit in Figure 1 demonstrates how the LT1332 may
be used with different types of switching regulators. Four
LT1332s are powered from a single PWM DC/DC converter
using an LT1172. Even with all twelve drivers heavily
loaded (R
compliant RS232 signals at 120k baud.
Operations with External Supplies
When external RS232 supplies are available (6.5V ≤ V
≤ 13.2V, –13.2V ≤ V
used as a stand-alone unit. Capacitor selection is
10µF
+
0.1µF
0.1µF
–
1µF
capacitor reduces ripple on the V
L
–
= 3k, C
capacitor should be 5 to 10 times bigger. As
V
C
3V V
+
–
LT1332
CC
ON/OFF
L
GND
GND
V
= 2500pF), the circuit generates fully
–
–
–
capacitor should be at least 1µF
–
+
≤ –6.2V) the LT1332 can be
capacitor where DC
10µF
–
capacitor at least 1/DC
+
0.1µF
0.1µF
1µF
V
C
3V V
–
+
–
LT1332
supply.
CC
LT1332
ON/OFF
GND
GND
V
MIN
–
is the
+
7
MIN
10µF
+