LT1945
Dual Micropower DC/DC
Converter with Positive and
Negative Outputs
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
Generates Well-Regulated Positive and
Negative Outputs
Low Quiescent Current:
20
µ
A in Active Mode (per Converter)
<1
µ
A in Shutdown Mode
Operates with V
IN
as Low as 1.2V
Low V
CESAT
Switch: 250mV at 300mA
Uses Small Surface Mount Components
High Output Voltage: Up to
±34V
Tiny 10-Pin MSOP Package
APPLICATIO S
s
s
s
s
Small TFT LCD Panels
Handheld Computers
Battery Backup
Digital Cameras
The LT
®
1945 is a dual micropower DC/DC converter in a
10-pin MSOP package. Each converter is designed with a
350mA current limit and an input voltage range of 1.2V to
15V, making the LT1945 ideal for a wide variety of appli-
cations. Both converters feature a quiescent current of
only 20µA at no load, which further reduces to 0.5µA in
shutdown. A current limited, fixed off-time control scheme
conserves operating current, resulting in high efficiency
over a broad range of load current. The 36V switch allows
high voltage outputs up to
±34V
to be easily generated
without the use of costly transformers. The LT1945’s low
off-time of 400ns permits the use of tiny, low profile
inductors and capacitors to minimize footprint and cost in
space-conscious portable applications.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
V
IN
2.7V
TO 5V
L1
10µH
8
V
IN
2
C1
4.7µF
4
SHDN2
3
7
9
SHDN1
LT1945
FB2
6
Dual Output (+12V, –20V) Converter
C4
0.1µF
D1
–20V
10mA
10
SW1
NFB1
1
D2
5
24.9k
C2
1µF
100pF
365k
85
+12V OUTPUT
80
EFFICIENCY (%)
90
75
70
65
60
GND PGND PGND SW2
115k
C3
1µF
12V
20mA
1945 TA01
55
50
0.1
1
10
LOAD CURRENT (mA)
100
1945 TA01a
4.7pF
L2
10µH
C1: TAIYO YUDEN JMK212BJ475
C2, C3: TAIYO YUDEN TMK316BJ105
C4: TAIYO YUDEN EMK107BJ104
D1, D2, D3: ZETEX ZHCS400
L1, L2: MURATA LQH3C100
D3
1M
U
Efficiency at V
IN
= 3.6V
–20V OUTPUT
1945f
U
U
1
LINER [ LINEAR TECHNOLOGY ]
