LT1332 LINER [Linear Technology], LT1332 Datasheet - Page 7

• Manufacturer Part Number: LT1332
• Description: Wide Supply Range Low Power RS232 Transceiver with 12V VPP Output for Flash Memory
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
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
operation of the charge pump resembles the switching
characteristics of the LT1237 and similar devices.
The V
on cross regulation and the regulator’s minimum duty
cycle to control V
tors so that when the regulator operates at minimum duty
cycle, sufficient charge will transfer to the V
to maintain a voltage of at least – 6.5V.
While only 0.1 F ceramic decoupling capacitors are needed
on the positive supply inputs, low ESR tantalum capaci-
ON/OFF
3V V
INPUT
–
CC
supply is not directly regulated. The circuit relies
2.7V < V
I(V
V
IN
0.1 F
0.1 F
+
IN
) < 14mA (UNLOADED)
1 F
IN
< 5.5V
+
–
68 F
. Select the C
U U
V
C
3V V
SHUTDOWN
+
–
LT1332
OPTIONAL
CC
GND
ON/OFF
V
IN
Figure 1. Multiple LT1332s Powered from a Single LT1172 DC/DC Converter
LT1172
GND
GND
V
VN2222LL
–
100 H
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
L1*
V
SW
FB
V
C
–
+
and V
10 F
W
+
0.1 F
0.1 F
1k
1N5817
1 F
0.1 F
–
storage capaci-
–
8V
storage cap
135k**
25k**
22 F
V
C
3V V
U
+
–
LT1332
CC
+
ON/OFF
GND
GND
V
–
TM
LT1332 • F01
**
+
*
L1 = SUMIDA CD105-101K OR COILCRAFT DO3316-104
1% METAL FILM
tors should be used in the charge pump to reduce voltage
losses. The C
capacitor should be 5 to 10 times bigger. As a rule of
thumb, make the V
bigger than the C
minimum duty cycle. Using large values for the V
tor reduces ripple on 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 con-
verter using an LT1172. Even with all twelve drivers
heavily loaded (R
fully compliant RS232 signals at 120k baud.
Operations with External Supplies
When external RS232 supplies are available (6.5V V
as a stand-alone unit. Capacitor selection is consider-
10 F
13.2V, – 13.2V V
+
0.1 F
0.1 F
1 F
V
C
3V V
–
+
–
capacitor should be at least 1 F and the V
LT1332
CC
–
ON/OFF
L
capacitor where DC
= 3k, C
GND
GND
V
–
–
–
capacitor at least 1/DC
L
– 6.2V) the LT1332 can be used
+
= 2500pF), the circuit generates
10 F
–
supply.
+
0.1 F
0.1 F
1 F
MIN
V
C
3V V
is the regulator’s
+
–
LT1332
CC
ON/OFF
LT1332
GND
GND
V
MIN
–
–
capaci-
times
+
7
10 F
–
+