LT3471 Linear Technology Corporation, LT3471 Datasheet

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LT3471

Manufacturer Part Number
LT3471
Description
Manufacturer
Linear Technology Corporation
Datasheet

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0
FEATURES
TYPICAL APPLICATIO
APPLICATIO S
CONTROL 1
CONTROL 2
1.2MHz Switching Frequency
Low V
High Output Voltage: Up to 40V
Wide Input Range: 2.4V to 16V
Inverting Capability
5V at 630mA from 3.3V Input
12V at 320mA from 5V Input
–12V at 200mA from 5V Input
Uses Tiny Surface Mount Components
Low Shutdown Current: < 1µA
Low Profile (0.75mm) 10-Lead 3mm × 3mm
DFN Package
Organic LED Power Supply
Digital Cameras
White LED Power Supply
Cellular Phones
Medical Diagnostic Equipment
Local ±5V or ±12V Supply
TFT-LCD Bias Supply
xDSL Power Supply
V
IN
CESAT
0.33µF
0.33µF
4.7k
4.7k
10µF
Switches: 330mV at 1.3A
3.3V
V
U
IN
SHDN/SS1
V
SHDN/SS2
IN
2.2µH
GND
V
IN
LT3471
SW1
10µH
OLED Driver
U
SW2
1µF
FB1N
FB2N
FB1P
FB2P
V
REF
15µH
0.1µF
105k
90.9k
3471 TA01
15k
10µF
15k
75pF
DESCRIPTIO
The LT
1.3A switches with error amplifiers that can sense to
ground providing boost and inverting capability. The low
V
current outputs in a small footprint. The LT3471 switches
at 1.2MHz, allowing the use of tiny, low cost and low
profile inductors and capacitors. High inrush current at
start-up is eliminated using the programmable soft-start
function, where an external RC sets the current ramp rate.
A constant frequency current mode PWM architecture
results in low, predictable output noise that is easy to filter.
The LT3471 switches are rated at 42V, making the device
ideal for boost converters up to ±40V as well as SEPIC and
flyback designs. Each channel can generate 5V at up to
630mA from a 3.3V supply, or 5V at 510mA from four
alkaline cells in a SEPIC design. The device can be config-
ured as two boosts, a boost and inverter or two inverters.
The LT3471 is available in a low profile (0.75mm) 10-lead
3mm × 3mm DFN package.
All other trademarks are the property of their respective owners.
CESAT
4.7µF
, LTC and LT are registered trademarks of Linear Technology Corporation.
®
bipolar switches enable the device to deliver high
V
7V
350mA
V
–7V
250mA
3471 dual switching regulator combines two 42V,
OUT1
OUT2
Dual 1.3A, 1.2MHz
U
3mm × 3mm DFN
Boost/Inverter in
90
85
80
75
70
65
60
55
50
95
0
OLED Driver Efficiency
100
V
V
OUT1
OUT1
I
OUT
= –7V
200
= 7V
(mA)
LT3471
300
3471 TA01b
3471fa
1
400

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LT3471 Summary of contents

Page 1

... SEPIC design. The device can be config- ured as two boosts, a boost and inverter or two inverters. The LT3471 is available in a low profile (0.75mm) 10-lead 3mm × 3mm DFN package. , LTC and LT are registered trademarks of Linear Technology Corporation. ...

Page 2

... Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT3471E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls ...

Page 3

... SHDN/SS Voltage 2 25°C A 1.8 1.6 1.4 1.2 1.0 0.8 0.6 CONTROL 1 AND 2 0.4 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2.0 V (V) SHDN/SS 3471 G08 LT3471 V Voltage vs V Current REF REF V REF VOLTAGE 100mV/DIV V CURRENT 200µA/DIV REF Switch Saturation Voltage vs Switch Current 800 700 600 90°C 500 400 300 200 100 0 100 0 0.2 0.4 0.6 ...

Page 4

... LT3471 CTIO S FB1N (Pin 1): Negative Feedback Pin for Switcher 1. Connect resistive divider tap here. Minimize trace area at FB1N. Set R1/R2), or connect to ground OUT FB1P for inverting topologies. FB1P (Pin 2): Positive Feedback Pin for Switcher 1. Con- nect either divided down version of V REF connect to a resistive divider tap for inverting topologies ...

Page 5

... Where V is the diode forward voltage drop and the worst case 330mV (at 1.3A) The LT3471 can be used at higher duty cycles, but it must be operated in the discontinuous conduction mode so that the actual duty cycle is reduced. Setting Output Voltage Setting the output voltage depends on the topology used. ...

Page 6

... ESR. Always use a capacitor with a sufficient voltage rating. Ceramic capacitors also make a good choice for the input decoupling capacitor, which should be placed as close as possible to the LT3471. A 4.7µF to 10µF input capacitor is . Normally SHDN/ and thus the impedance looks ...

Page 7

... C3 PL 33pF 90.9k 4.7µF R4 15k C2 0.1µF R2 15k C6 R1 75pF 105k V OUT2 –7V C4 10µF 3471 F02 Supply Current of Figure 2 During Start-Up with Soft-Start RC Network OUT1 0.2ms/DIV ) in parallel with the resistor (R3) PL and V as shown in Figure 2. The frequency OUT FB LT3471 3471 F02c 3471fa 7 ...

Page 8

... U V VOLTAGE REFERENCE REG Pin 3 of the LT3471 is a bandgap voltage reference that has been divided down to 1.00V and buffered for external use. This pin must be bypassed with at least 0.01µF and no more than 1µF. This will ensure stability as well as reduce the noise on this pin. The buffer has a built-in current limit of at least 1mA (typically 1 ...

Page 9

... Like all other current mode switching regulators, the LT3471 needs to be compensated for stable and efficient operation. Two feedback loops are used in the LT3471: a fast current loop which does not require compensation, and a slower voltage loop which does. Standard Bode plot analysis can be used to understand and adjust the voltage feedback loop ...

Page 10

... LT3471 U U APPLICATIONS INFORMATION – 1.00V + REFERENCE – COMPENSATION CAPACITOR OUTPUT CAPACITOR OUT C : PHASE LEAD CAPACITOR TRANSCONDUCTANCE AMPLIFIER INSIDE POWER STAGE TRANSCONDUCTANCE AMPLIFIER COMPENSATION RESISTOR OUTPUT RESISTANCE DEFINED ...

Page 11

... –7V OUT 100 200 300 400 I (mA) OUT 3471 TA02b LT3471 V OUT1 500mA WHEN V = 4.2V IN 90.9k 4.7µF 350mA WHEN V = 3.3V IN 250mA WHEN 15k R2 15k C6 R1 75pF 105k V OUT2 –7V TO –4V C4 –7V WHEN CONTROL 10µ ...

Page 12

... Single Li-Ion Cell to 5V, 12V Boost Converter L1 D1 3.3µ SW1 9 1 SHDN/SS1 FB1N 2 FB1P 3 V REF LT3471 IN 0.1µF 4 FB2P 7 5 SHDN/SS2 FB2N GND SW2 6.8µ C1-C3: X5R OR X7R 6.3V L1: SUMIDA CR43-3R3 C4: X5R OR X7R 16V L2: SUMIDA CR43-6R8 D1, D2: ON SEMICONDUCTOR MBRM-120 ...

Page 13

... FB2P 7 5 SHDN/SS2 FB2N GND SW2 2.2µ C1, C2: X5R OR X7R 6.3V C3, C4: X5R OR X7R 50V D1, D2: ON SEMICONDUCTOR MBRM-140 L1, L2: SUMIDA CDRH2D-2R2 LT3471 C3 I OUT1 0.22µF 20mA R1 10 WHITE LEDs 90.9k R2 10k 4.99Ω OUT2 0.22µF 20mA 10 WHITE LEDs 4.99Ω 3471 TA04 ...

Page 14

... C4, C6: X5R OR X7R 6.3V D1, D2: ON SEMICONDUCTOR MBRM-120 L1-L4: MURATA LQH43CN100K032 14 Li-Ion or 4-Cell Alkaline to 3.3V and 5V SEPIC C3 L1 4.7µF D1 10µ 10µH 10 SW1 1 SHDN/SS1 FB1N 2 FB1P 3 V REF C2 V LT3471 IN 0.1µF 4 FB2P 5 SHDN/SS2 FB2N GND SW2 10µF D2 10µ 10µH V OUT1 3.3V 640mA ...

Page 15

... ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE LT3471 R = 0.115 0.38 ± 0.10 TYP 6 10 ...

Page 16

... McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● ±12V Dual Supply Boost/Inverting Converter L1 D1 10µ SW1 9 1 SHDN/SS1 FB1N 2 FB1P 3 V REF LT3471 IN 0.1µ 4.7µF FB2P 7 5 SHDN/SS2 FB2N GND SW2 11 6 • • 10µH 10µ ...

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