LT1614CMS8 Linear Technology, LT1614CMS8 Datasheet - Page 11

• Manufacturer Part Number: LT1614CMS8
• Description: IC SW REG INVERTING 600KHZ 8MSOP
• Manufacturer: Linear Technology
• Type: Invertingr

Specifications of LT1614CMS8

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adj to -24V
• Current - Output: 500mA
• Frequency - Switching: 600kHz
• Voltage - Input: 0.92 ~ 5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

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 13.
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. The low-battery detector is dis-
abled when SHDN is low.
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 14
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 15. The low-
battery detect is not operative when the device is shut
down.
BE
. The LT1614 doesn’t know what to do in this situation
SHDN
Figure 13. 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 F13
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 16. Be sure to
get the phasing right.
V
5V
IN
+
Figure 16. 5V to – 5V Converter with Coupled Inductor
C1, C2: AVX TAJB336M010
C3: AVX 1206CY106
D1: MBR0520
L1: COILTRONICS CTX10-1
Figure 14. Setting Low-Battery Detector Trip Point
C1
33 F
R1
R2
100k
100k
Figure 15. Accessing 200mV Reference
1nF
200mV
LBI
V
REF
2N3906
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 F14
69.8k
24.9k
LBO
LBI
3.3V
•
D1
LT1614
1M
10 H
R1 =
GND
V
L1B
IN
1614 F15
TO PROCESSOR
V
LB
LT1614
+
– 200mV
2 A
1614 F16
C2
33 F
V
– 5V
200mA
11
OUT