LT1931/LT1931A
1.2MHz/2.2MHz Inverting
DC/DC Converters in ThinSOT
FEATURES
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DESCRIPTIO
Fixed Frequency 1.2MHz/2.2MHz Operation
Very Low Noise: 1mV
P-P
Output Ripple
– 5V at 350mA from 5V Input
–12V at 150mA from 5V Input
Uses Small Surface Mount Components
Wide Input Range: 2.6V to 16V
Low Shutdown Current: <1µA
Low V
CESAT
Switch: 400mV at 1A
Low Profile (1mm) ThinSOT
TM
Package
Pin-for-Pin Compatible with the LT1611
APPLICATIO S
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The LT
®
1931/LT1931A are the industry’s highest power
inverting SOT-23 current mode DC/DC converters. Both
parts include a 1A integrated switch allowing high current
outputs to be generated in a small footprint. The LT1931
switches at 1.2MHz while the LT1931A switches at 2.2MHz.
These high speeds enable the use of tiny, low cost
capacitors and inductors 2mm or less in height. The
LT1931 is capable of generating – 5V at 350mA or –12V
at 150mA from a 5V supply, while the LT1931A can
generate –5V at 300mA using significantly smaller induc-
tors. Both parts are easy pin-for-pin upgrades for higher
power LT1611 applications.
The LT1931/LT1931A operate in a dual inductor inverting
topology that filters both the input side and output side
current. Very low output voltage ripple approaching 1mV
P-P
can be achieved when ceramic output capacitors are used.
Fixed frequency switching ensures a clean output free
from low frequency noise typically present with charge
pump solutions. The low impedance output remains within
1% of nominal during large load steps. The 36V switch
allows V
IN
to V
OUT
differential of up to 34V.
The LT1931/LT1931A are available in the 5-lead ThinSOT
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
Disk Drive MR Head Bias
Digital Camera CCD Bias
LCD Bias
GaAs FET Bias
Local Low Noise/Low Impedance Negative Supply
TYPICAL APPLICATIO
V
IN
5V
V
IN
SHDN
C1
4.7µF
LT1931
NFB
GND
L1A
10µH
C2
1µF
L1B
10µH
100
95
D1
SW
R1
29.4k
R2
10k
C4
220pF
EFFICIENCY (%)
V
OUT
–5V
350mA
C3
22µF
90
85
80
75
70
65
60
C1: TAIYO YUDEN X5R JMK212BJ475MG
C2: TAIYO YUDEN X5R LMK212BJ105MG
C3: TAIYO YUDEN X5R JMK325BJ226MM
D1: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CLS62-100
1931 F01
55
50
0
50
100 150 200 250
LOAD CURRENT (mA)
300
350
Figure 1. 5V to –5V, 350mA Inverting DC/DC Converter
U
Efficiency
1931 TA01
U
U
1
ETC [ ETC ]
