LT1946
1.2MHz Boost
DC/DC Converter with
1.5A Switch and Soft-Start
FEATURES
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DESCRIPTIO
1.5A, 36V Internal Switch
1.2MHz Switching Frequency
Integrated Soft-Start Function
Output Voltage Up to 34V
Low V
CESAT
Switch: 300mV at 1.5A (Typ)
8V at 430mA from a 3.3V Input
Small 8-Lead MSOP Package
APPLICATIO S
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TFT-LCD Bias Supplies
GPS Receivers
DSL Modems
Local Power Supplies
The LT
®
1946 is a fixed frequency step-up DC/DC converter
containing an internal 1.5A, 36V switch. Capable of gener-
ating 8V at 430mA from a 3.3V input, the LT1946 is ideal
for large TFT-LCD panel power supplies. The LT1946
switches at 1.2MHz, allowing the use of tiny, low profile
inductors and low value ceramic capacitors. Loop com-
pensation can be either internal or external, giving the user
flexibility in setting loop compensation and allowing opti-
mized transient response with low ESR ceramic output
capacitors. Soft-start is controlled with an external capaci-
tor, which determines the input current ramp rate during
start-up.
The 8-lead MSOP package and high switching frequency
ensure a low profile overall solution less than 1.2mm high.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
V
IN
3.3V
3
1
L1
4.7µH
6
V
IN
SHDN
LT1946
V
C
SS
C
SS
100nF
8
7
FB
COMP GND
4
OFF ON
C1
2.2µF
R
C
49.9k
C
C
470pF
5
SW
D1
90
V
OUT
8V
430mA
85
80
EFFICIENCY (%)
R1
28.7k
2
R2
5.23k
C2
20µF
75
70
65
60
55
C1: 2.2µF, X5R OR X7R, 6.3V
C2: 2
×
10µF, X5R OR X7R, 10V
D1: MICROSEMI UPS120 OR EQUIVALENT
L1: TDK RLF5018T-4R7M1R4
1946 F01
50
0
100
Figure 1. 3.3V to 8V, 430mA Step-Up DC/DC Converter
U
Efficiency
400
300
LOAD CURRENT (mA)
200
500
1946 F01b
U
U
sn1946 1946fs
1
LINER [ LINEAR TECHNOLOGY ]
