Datasheet

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LT3471

3471fb

TYPICAL APPLICATION

DESCRIPTION

Dual 1.3A, 1.2MHz

Boost/Inverter in

3mm × 3mm DFN

FEATURES

APPLICATIONS

1.2MHz Switching Frequency

Low V

CESAT

Switches: 330mV at 1.3A

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 Proﬁ le (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

The LT

3471 dual switching regulator combines two 42V,

1.3A switches with error ampliﬁ ers that can sense to

ground providing boost and inverting capability. The low

CESAT

bipolar switches enable the device to deliver high

current outputs in a small footprint. The LT3471 switches

at 1.2MHz, allowing the use of tiny, low cost and low proﬁ le

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 ﬁ lter.

The LT3471 switches are rated at 42V, making the device

ideal for boost converters up to ±40V as well as SEPIC

and ﬂ yback 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

conﬁ gured as two boosts, a boost and inverter or two

inverters.

The LT3471 is available in a low proﬁ le (0.75mm) 10-lead

3mm × 3mm DFN package.

4.7k

CONTROL 1

3471 TA01

0.33μF

10μF

4.7k

CONTROL 2

0.33μF

SHDN/SS1 FB1N

SW1

SW2

LT3471

10μH

15μH

GND

FB1P

3.3V

FB2P

FB2N

REF

0.1μF

4.7μF

OUT1

350mA

OUT2

–7V

250mA

75pF

15k

90.9k

15k

105k

1μF

SHDN/SS2

10μF

2.2μH

OUT

(mA)

EFFICIENCY (%)

400

3471 TA01b

100

200

300

OUT1

= 7V

OUT1

= –7V

OLED Driver Efﬁ ciency

OLED Driver

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

Summary of content (16 pages)

PAGE 1
LT3471 Dual 1.3A, 1.2MHz Boost/Inverter in 3mm × 3mm DFN DESCRIPTION FEATURES n n n n n n n n n n n The LT®3471 dual switching regulator combines two 42V, 1.3A switches with error ampliﬁers that can sense to ground providing boost and inverting capability. The low VCESAT bipolar switches enable the device to deliver high 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.
PAGE 2
LT3471 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) VIN Voltage ................................................................16V SW1, SW2 Voltage ..................................... –0.4V to 42V FB1N, FB1P, FB2N, FB2P Voltage......... 12V or VIN – 1.5V SHDN/SS1, SHDN/SS2 Voltage ............................... 16V VREF Voltage.............................................................1.5V Maximum Junction Temperature ........................ 125°C Operating Temperature Range (Note 2) ...
PAGE 3
LT3471 ELECTRICAL CHARACTERISTICS The ● denotes speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are TA = 25°C. VIN = VSHDN = 3V unless otherwise noted. PARAMETER CONDITIONS SHDN Input Voltage Low Quiescent Current ≤ 1μA MIN SHDN Pin Bias Current VSHDN = 3V, VIN = 4V VSHDN = 0V TYP 22 0 Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device.
PAGE 4
LT3471 TYPICAL PERFORMANCE CHARACTERISTICS Peak Switch Current vs SHDN/SS Voltage 1.50 2.0 1.45 1.8 1.40 1.6 SWITCH CURRENT (A) FREQUENCY (MHz) Oscillator Frequency vs Temperature 1.35 1.30 1.25 1.20 1.15 125 VOUT2 5V/DIV CONTROL 1 AND 2 5V/DIV 0.8 0.6 0.2 100 VOUT1 2V/DIV 1.0 1.05 50 25 0 75 TEMPERATURE (°C) ISUPPLY 1A/DIV 1.2 0.4 –25 TA = 25°C 1.4 1.10 1.00 –50 Start-Up Waveform (Figure 2 Circuit) 0 0.5ms/DIV 0 3471 G09 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2.
PAGE 5
LT3471 BLOCK DIAGRAM 2 FB1P 10 SW1 + – A1 1 FB1N – RC + CC 8 VIN 1.00V REFERENCE VREF DRIVER A2 R S Q1 Q + 3 ∑ 0.01Ω – 9 4 SHDN/SS1 FB2P RAMP GENERATOR LEVEL SHIFTER 6 SW2 + – A3 5 FB2N – RC + CC 7 SHDN/SS2 11 GND LEVEL SHIFTER DRIVER A4 R S Q2 Q + ∑ 0.01Ω – RAMP GENERATOR GND 1.2MHz OSCILLATOR 3471 F01 Figure 1. Block Diagram OPERATION The LT3471 uses a constant frequency, current mode control scheme to provide excellent line and load regulation.
PAGE 6
LT3471 OPERATION current reaches this value, the SR latch is reset regardless of the state of the comparator A2 (A4). Also not shown in the Block Diagram is the thermal shutdown circuit. If the temperature of the part exceeds approximately 160°C, both latches are reset regardless of the state of comparators A2 and A4. The current limit and thermal shutdown circuits protect the power switch as well as the external components connected to the LT3471.
PAGE 7
LT3471 APPLICATIONS INFORMATION Soft-Start and Shutdown Features CAPACITOR SELECTION To shut down the part, ground both SHDN/SS pins. To shut down one switcher but not the other one, ground that switcher’s SHDN/SS pin. The soft-start feature provides a way to limit the inrush current drawn from the supply upon start-up. To use the soft-start feature for either switcher, slowly ramp up that switcher’s SHDN/SS pin.
PAGE 8
LT3471 APPLICATIONS INFORMATION L1 2.2μH D1 VIN RSS1 4.7k CONTROL 1 1.8V 0V 10 9 SHDN/SS1 SW1 FB1N CSS1 0.33μF VIN 2.6V TO 4.2V Li-Ion FB1P 8 10μF RSS2 4.7k CONTROL 2 1.8V 0V CSS2 0.33μF VREF VIN 1 2 VOUT1 7V C3 4.7μF C2 0.1μF SHDN/SS2 GND SW2 11 6 FB2P L2 10μH R3 90.9k R4 15k 3 LT3471 FB2N 7 CPL 33pF 5 R2 15k 4 3471 F02 C5 1μF L3 15μH R1 105k C6 75pF VOUT2 –7V VIN C4 10μF D2 C1, C2: X5R OR X7R 6.
PAGE 9
LT3471 APPLICATIONS INFORMATION By choosing the appropriate values for the resistor and capacitor, the zero frequency can be designed to improve the phase margin of the overall converter. The typical target value for the zero frequency is between 35kHz to 55kHz. Figure 3 shows the transient response of the step-up converter from Figure 2 without the phase lead capacitor CPL.
PAGE 10
LT3471 APPLICATIONS INFORMATION DIODE SELECTION Compensation—Theory A Schottky diode is recommended for use with the LT3471. For high efﬁciency, a diode with good thermal characteristics at high currents should be used such as the On Semiconductor MBRM120. This is a 20V diode. Where the switch voltage exceeds 20V, use the MBRM140, a 40V diode. These diodes are rated to handle an average forward current of 1.0A. In applications where the average forward current of the diode is less than 0.
PAGE 11
LT3471 APPLICATIONS INFORMATION From Figure 6, the DC gain, poles and zeroes can be calculated as follows: Output Pole: P1= 2 2 • π • RL • COUT Value Units RL 20 Ω Application Speciﬁc COUT 4.7 μF Application Speciﬁc RESR 10 mΩ Application Speciﬁc RO 0.9 MΩ Not Adjustable CC 90 pF Not Adjustable CPL 33 pF Adjustable RC 55 kΩ Not Adjustable 1 R1 90.9 kΩ Adjustable 2 • π • RESR • COUT R2 15 kΩ Adjustable VOUT 7 V VIN 3.3 V gma 50 μmho Not Adjustable gmp 9.
PAGE 12
LT3471 TYPICAL APPLICATIONS Li-Ion OLED Driver L1 2.2μH D1 VIN CONTROL 1 1.8V 0V VIN 2.6V TO 4.2V Li-Ion CONTROL 2 1.8V 0V RSS1 4.7k 10 9 SHDN/SS1 SW1 FB1N CSS1 0.33μF FB1P 8 C1 10μF RSS2 4.7k CSS2 0.33μF VREF VIN 7 1 2 SHDN/SS2 GND FB2P VCONTROL C2 0.1μF 0V TO 1V R5 20k 5 4 6 L2 15μH VOUT1 7V 500mA WHEN VIN = 4.2V 350mA WHEN VIN = 3.3V 250mA WHEN VIN = 2.6V R2 15k R6 10k SW2 11 C3 4.7μF R4 15k 3 LT3471 FB2N R3 90.
PAGE 13
LT3471 TYPICAL APPLICATIONS Single Li-Ion Cell to 5V, 12V Boost Converter L1 3.3μH C3 10μF VOUT1 5V 900mA IF VIN = 4.2V 630mA IF VIN = 3.3V 425mA IF VIN = 2.6V C4 10μF VOUT2 12V 300mA IF VIN = 4.2V 210mA IF VIN = 3.3V 145mA IF VIN = 2.6V D1 VIN CONTROL 1 1.8V OV 9 SHDN/SS1 SW1 FB1N CSS1 0.33μF FB1P 8 VIN 2.6V TO 4.2V CONTROL 2 1.8V 0V 10 RSS1 4.7k RSS2 4.7k VREF VIN CSS2 0.33μF 2 C2 0.1μF FB2P SHDN/SS2 GND 11 R1 20k R2 4.99k 3 LT3471 C1 4.7μF 7 C5 100pF 1 FB2N 4 5 SW2 L2 6.
PAGE 14
LT3471 TYPICAL APPLICATIONS Li-Ion 20 White LED Driver L1 2.2μH D1 VIN CONTROL 1 1.8V OV 9 SHDN/SS1 SW1 FB1N CSS1 0.33μF FB1P 8 VIN 2.6V TO 4.2V CONTROL 2 1.8V OV C3 0.22μF 10 RSS1 4.7k RSS2 4.7k VREF VIN CSS2 0.33μF 2 3 C2 0.1μF FB2P 7 1 LT3471 C1 4.7μF SHDN/SS2 GND FB2N IOUT1 20mA 4 R1 90.9k 10 WHITE LEDs R2 10k 5 SW2 11 6 3471 TA04 4.99Ω L2 2.2μH VIN D2 C4 0.22μF IOUT2 20mA C1, C2: X5R OR X7R 6.
PAGE 15
LT3471 TYPICAL APPLICATIONS Li-Ion or 4-Cell Alkaline to 3.3V and 5V SEPIC C3 4.7μF L1 10μH D1 VIN CONTROL 1 1.8V OV 10 RSS1 4.7k 9 SW1 SHDN/SS1 RSS2 4.7k SHDN/SS2 GND R1 34.8k C2 0.1μF LT3471 4 FB2P 7 C4 15μF R2 15k 3 VREF VIN C1 4.7μF CSS2 0.33μF 2 FB1P 8 C7 56pF 1 FB1N CSS1 0.33μF VIN 2.6V TO 6.5V CONTROL 2 1.8V OV L2 10μH VOUT1 3.3V 640mA AT VIN = 6.5V 550mA AT VIN = 5V 470mA AT VIN = 4V 410mA AT VIN = 3.3V 340mA AT VIN = 2.
PAGE 16
LT3471 TYPICAL APPLICATIONS 5V to ±12V Dual Supply Boost/Inverting Converter L1 10μH D1 VIN 10 CONTROL 1 1.8V OV 4.7k 9 SHDN/SS1 SW1 FB1N FB1P 0.33μF 8 VIN 5V CONTROL 2 1.8V OV VREF VIN 0.33μF SHDN/SS2 GND FB2N 4 5 C7 56pF 6 3471 TA06 • VIN R3 15k SW2 11 L2 10μH C3 4.7μF R2 4.99k 3 C2 0.1μF FB2P 7 2 LT3471 C1 4.7μF 4.7k R1 C6 56pF 54.9k 1 VOUT1 12V 320mA R4 182k • C5 1μF D2 C1, C2: X5R OR X7R 6.