LT1935 Linear Technology, LT1935 Datasheet

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LT1935

Manufacturer Part Number
LT1935
Description
DC/DC Converter
Manufacturer
Linear Technology
Datasheet

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FEATURES
TYPICAL APPLICATIO
APPLICATIO S
1.2MHz Switching Frequency
High Output Voltage: Up to 38V
Wide Input Range: 2.3V to 16V
Low V
Soft-Start
Uses Small Surface Mount Components
5V at 1A from 3.3V Input
12V at 600mA from 5V Input
Low Shutdown Current: < 1µA
Pin-for-Pin Compatible with the LT1613 and LT1930
Low Profile (1mm) SOT-23 (ThinSOT
Digital Cameras
Battery Backup
LCD Bias
Local 5V or 12V Supply
PC Cards
xDSL Power Supply
TFT-LCD Bias Supply
V
5V
Figure 1. 5V to 12V, 600mA Step-Up DC/DC Converter
IN
CESAT
D1: ON SEMI MBRM120
L1: SUMIDA CDRH5D28-4R2
ON OFF
4.7µF
Switch: 180mV at 2A
SHDN
U
V
IN
LT1935
4.2µH
GND
L1
SW
FB
D1
U
10k
84.5k
TM
) Package
1935 F01
10µF
V
12V
600mA
OUT
DESCRIPTIO
ThinSOT is a trademark of Linear Technology Corporation.
The LT
switching regulator. Its unprecedented 2A, 40V internal
switch allows high output currents to be generated in a
small footprint. Intended for space-conscious applica-
tions, the LT1935 switches at 1.2MHz, allowing the use of
tiny, low profile inductors and capacitors 2mm or less in
height. The NPN switch achieves a V
at 2A independent of supply voltage, resulting in high
efficiency even at maximum power levels from a 3V input.
A constant frequency, internally compensated, current
mode PWM architecture results in low, predictable output
noise that is easy to filter. Low ESR ceramic capacitors can
be used on the output, further reducing noise to the
millivolt level. The high voltage switch on the LT1935 is
rated at 40V, making the device ideal for boost converters
up to 38V as well as for single-ended primary inductance
converter (SEPIC) and flyback designs. The device can
generate 5V at up to 1A from a 3.3V supply or 5V at 550mA
from four alkaline cells in a SEPIC design.
The LT1935 is available in a 5-lead SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
®
1935 is the industry’s highest power SOT-23
1.2MHz Boost DC/DC
Converter in ThinSOT
90
85
80
75
70
65
60
55
50
0
U
100
Efficiency, V
with 2A Switch
200
LOAD CURRENT (mA)
300
V
IN
400
= 3.3V
OUT
CESAT
V
= 12V
IN
500
= 5V
600
of just 180mV
1935 F01b
LT1935
700
1
1935f

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LT1935 Summary of contents

Page 1

... Its unprecedented 2A, 40V internal switch allows high output currents to be generated in a small footprint. Intended for space-conscious applica- tions, the LT1935 switches at 1.2MHz, allowing the use of tiny, low profile inductors and capacitors 2mm or less in height. The NPN switch achieves independent of supply voltage, resulting in high efficiency even at maximum power levels from a 3V input ...

Page 2

... SHDN Input High Voltage SHDN Input Low Voltage Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT1935ES5 is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C operating 2 U ...

Page 3

... SWITCH CURRENT (A) Frequency Foldback 1 25°C A 1.2 1.0 0.8 0.6 0.4 0 0.2 FEEDBACK VOLTAGE (V) 1935 G07 LT1935 Undervoltage Lockout 2.4 2.3 2.2 2.1 2.0 1.9 1.8 125 –50 – TEMPERATURE (°C) 1935 G02 Peak Switch Current vs SHDN Pin Voltage (Soft-Start) 4 50% DUTY CYCLE T = 25° 3 ...

Page 4

... FB R2 (EXTERNAL) U OPERATIO The LT1935 uses a constant frequency, current mode control scheme to provide excellent line and load regula- tion. Operation can be best understood by referring to the Block Diagram in Figure 2. At the start of each oscillator cycle, the SR latch is set, turning on the power switch Q1. ...

Page 5

... Use a 4.7µF ceramic capacitor to bypass the input of the LT1935. Be aware that the switching regulators require a low impedance input supply. Additional bulk capacitance may be required if the LT1935 circuit is more than a few inches away from the power source. If there are low ESR capacitors nearby, the input bypass capacitor can be reduced to 2.2µ ...

Page 6

... W U Soft Start The SHDN pin can be used to soft start the LT1935, reducing the maximum input current during start up. The SHDN pin is driven through an external RC filter to create a ramp at this pin. Figure 6 shows the start-up waveforms with and without the soft start circuit. Without soft start, the input current peaks at ~3A ...

Page 7

... JEDEC PACKAGE REFERENCE IS MO-193 Efficiency OUT 3. 2. 200 400 600 800 1000 LOAD CURRENT (mA) V OUT 12V 320mA R1 84.5k C2 22µF R2 10k 1935 TA02 2.90 BSC (NOTE 4) 0.30 – 0.45 TYP 5 PLCS (NOTE 3) 0.01 – 0.10 1.90 BSC S5 TSOT-23 0302 LT1935 1200 1935f 7 ...

Page 8

... C3: X5R OR X7R 25V D1: MBRM120 OR EQUIVALENT D2, D3: BAT-54S OR EQUIVALENT L1: SUMIDA CDRH4D28-2R2 5V SEPIC Converter C3 L1 2.2µF 4.7µ 47pF 4.7µF 29.4k LT1935 ON OFF SHDN FB GND R2 10k C1, C3: X5R OR X7R 10V D1: ON SEMI MBRM120 C2: X5R OR X7R 6.3V L1, L2: SUMIDA CDRH4D18-4R7 www.linear.com ● 16V 10mA C3 1µF ...

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