LT1614 Linear Technology, LT1614 Datasheet - Page 5

• Manufacturer Part Number: LT1614
• Description: Inverting 600kHz Switching Regulator
• Manufacturer: Linear Technology

APPLICATIONS
Shutdown Pin
The LT1614 has a Shutdown pin (SHDN) that must be
grounded to shut the device down or tied to a voltage equal
or greater than V
shown in Figure 1.
Note that allowing SHDN to float turns on both the start-
up current (Q2) and the shutdown current (Q3) for V
2V
and behaves erratically. SHDN voltage above V
lowed. This merely reverse-biases Q3’s base emitter junc-
tion, a benign condition.
Low-Battery Detector
The LT1614’s low-battery detector is a simple PNP input
gain stage with an open collector NPN output. The nega-
tive input of the gain stage is tied internally to a 200mV
reference. The positive input is the LBI pin. Arrangement
as a low-battery detector is straightforward. Figure 2
details hookup. R1 and R2 need only be low enough in
value so that the bias current of the LBI pin doesn’t cause
large errors. For R2, 100k is adequate. The 200mV refer-
ence can also be accessed as shown in Figure 3.
BE
. The LT1614 doesn’t know what to do in this situation
SHDN
Figure 1. Shutdown Circuit
IN
U
to operate. The shutdown circuit is
INFORMATION
U
Q1
R2
400k
200k
V
IN
W
Q3
Q2
SHUTDOWN
CURRENT
START-UP
CURRENT
1614 F01
U
IN
is al-
IN
>
Coupled Inductors
The applications shown in this data sheet use two un-
coupled inductors because the Murata units specified are
small and inexpensive. This topology can also be used
with a coupled inductor as shown in Figure 4. Be sure to
get the phasing right.
V
5V
IN
+
Figure 4. 5V to – 5V Converter with Coupled Inductor
C1, C2: AVX TAJB336M010
C3: AVX 1206CY106
D1: MBR0520
L1: COILTRONICS CTX10-1
Figure 2. Setting Low-Battery Detector Trip Point
R1
R2
100k
C1
33 F
100k
Figure 3. Accessing 200mV Reference
1nF
200mV
LBI
V
2N3906
REF
SHDN
V
V
GND
C
IN
200mV
INTERNAL
REFERENCE
+
–
LT1614
10 H
L1A
GND
10k
V
IN
•
SW
NFB
+
200k
LT1614
10 F
1 F
C3
LBO
1614 F02
69.8k
24.9k
LBO
LBI
3.3V
•
D1
1M
LT1614
R1 =
GND
10 H
V
L1B
IN
1614 F03
TO PROCESSOR
V
LB
LT1614
– 200mV
+
2 A
1614 F04
C2
33 F
V
– 5V
200mA
OUT
5