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LT3479

3479fc

TYPICAL APPLICATION

DESCRIPTION

3A, Full Featured DC/DC

Converter with Soft-Start

and Inrush Current Protection

The LT

3479 is a current mode, ﬁ xed frequency step-up

DC/DC converter with an internal 3A, 42V switch. Efﬁ cien-

cies of up to 89% can be achieved in typical applications. It

features a programmable soft-start function to limit induc-

tor current during start-up and inrush current protection

to protect the LT3479 during shorts and line transients.

Both inputs of the error ampliﬁ er are available to the user

allowing positive and negative output voltages. Through

an external resistor, the user can program the switch-

ing frequency from 200kHz to 3.5MHz. The low proﬁ le

(0.75mm) 14-pin, 4mm × 3mm DFN package provides

excellent thermal performance in a small footprint. The

LT3479 is also available in a thermally enhanced 16-pin

TSSOP package.

5V to 12V Boost Converter

FEATURES

APPLICATIONS

High Power LED Driver

DSL Modems

Distributed Power

Wide Input Voltage Range: 2.5V to 24V

3A, 42V Internal Switch

High Efﬁ ciency Power Conversion: Up to 89%

Soft-Start

Frequency Set by External Resistor: 200kHz to

3.5MHz

Protection Against Input Short Circuits and

Hot Plugging

Low V

CESAT

Switch: 0.3V at 2.5A (Typical)

Capable of Positive and Negative Outputs

Available in Thermally Enhanced 14-Lead

(4mm × 3mm) DFN and 16-Lead TSSOP Packages

5V to 12V Efﬁ ciency

200k

23.2k

17.8k

10k

2.2μF

4.7μH

3479 TA01

FBN

SWLV

GNDR

REF

SHDN

LT3479

FBP

2.2nF

10μF

OUT

12V

0.8A

10nF

OUT

(A)

EFFICIENCY (%)

0.8

3479 TA02

0.2

0.4

0.6

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

Summary of content (20 pages)

PAGE 1
LT3479 3A, Full Featured DC/DC Converter with Soft-Start and Inrush Current Protection FEATURES DESCRIPTION n The LT®3479 is a current mode, ﬁxed frequency step-up DC/DC converter with an internal 3A, 42V switch. Efﬁciencies of up to 89% can be achieved in typical applications. It features a programmable soft-start function to limit inductor current during start-up and inrush current protection to protect the LT3479 during shorts and line transients.
PAGE 2
LT3479 ABSOLUTE MAXIMUM RATINGS (Note 1) SW, L, VS Voltages ................................................... 42V VIN, SHDN Voltages ................................................. 24V FBP, FBN, VREF, RT, VC Voltages ................................. 2V Junction Temperature .......................................... 125°C Operating Temperature Range (Note 2).... –40°C to 85°C Storage Temperature Range................... –65°C to 125°C Lead Temperature (Soldering, 10 sec) TSSOP .......................
PAGE 3
LT3479 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 2.5V, VSHDN = 2.5V. PARAMETER CONDITIONS MIN l Minimum Input Voltage Quiescent Current VIN = 2.5V, VSHDN = 0V VIN = 2.5V, VSHDN = 2.5V, VC = 0.3V (Not Switching) Reference Voltage Measured at VREF Pin Reference Voltage Line Regulation 2.5V < VIN < 24V, VC = 0.3V Maximum VREF Pin Current Out of Pin Soft-Start Pin Current SS = 0.
PAGE 4
LT3479 TYPICAL PERFORMANCE CHARACTERISTICS Switch VCE(SAT) Inductor and Switch Current Limit VREF 6 0.5 1.27 INDUCTOR CURRENT LIMIT 0.3 25°C –50°C 0.2 0.1 0.5 1 1.5 2 SWITCH CURRENT (A) 2.5 3 1.25 SWITCH CURRENT LIMIT 3 VIN = 24V 1.24 VIN = 2.5V 2 1.23 1 1.22 0 –50 –25 0 0 4 VREF (V) CURRENT (A) 125°C VCE(SAT) (V) 1.26 5 0.4 50 25 75 0 TEMPERATURE (°C) 100 1.21 –50 –25 125 SHDN Pin Turn-On Threshold 3479 G03 SHDN Pin Current VIN Pin Current 50 1.
PAGE 5
LT3479 PIN FUNCTIONS (DFN/TSSOP) SW (Pins 1, 2/Pins 1, 2): Switch Pins. Collector of the internal NPN power switch. Connect the inductor and diode here and minimize the metal trace area connected to this pin to minimize electromagnetic interference. FBP (Pin 9/Pin 10): The Noninverting Input to the Error Ampliﬁer. Connect resistive divider tap here for negative output voltage. L (Pin 3/Pin 3): Inductor Pin. Connect the inductor to this pin.
PAGE 6
LT3479 BLOCK DIAGRAM D1 L1 RC CC CSS CS C1 R1 FB VS SS FBP + FEEDBACK AMPLIFIER R2 8.5mW INRUSH CURRENT PROTECTION COMPARATOR + FBN SW L + – 36mV VC – – VREF SHDN ICON MASTER LATCH + pwmout 1.
PAGE 7
LT3479 OPERATION The LT3479 uses a ﬁxed frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the Block Diagram. The start of each oscillator cycle sets the SR latch and turns on power switch Q1. The signal at the inverting input of the PWM comparator (SLOPE) is proportional to the sum of the switch current and oscillator ramp.
PAGE 8
LT3479 APPLICATIONS INFORMATION Capacitor Selection Low ESR (equivalent series resistance) ceramic capacitors should be used at the output to minimize the output ripple voltage. Use only X5R or X7R dielectrics, as these materials retain their capacitance over wider voltage and temperature ranges better than other dielectrics. A 4.7μF to 10μF output capacitor is sufﬁcient for most high output current designs. Converters with lower output currents may need only a 1μF or 2.2μF output capacitor. Table 1.
PAGE 9
LT3479 APPLICATIONS INFORMATION Diode Selection Setting Negative Output Voltages Schottky diodes, with their low forward voltage drop and fast switching speed, are ideal for LT3479 applications. Table 3 lists several Schottky diodes that work well with the LT3479. The diode’s average current rating must exceed the average output current. The diode’s maximum reverse voltage must exceed the output voltage.
PAGE 10
LT3479 APPLICATIONS INFORMATION MINIMIZE THE AREA OF THIS TRACE TO VOUT D COUT L1 CC TO VS SW GND SW GND CS CIN RT RC SS L VC LT3479 VS TO VIN CSS VIN FBN RT FBP R1 VREF SHDN R2 TO GND 3479 F04 TO SHDN PLACE VIAS AROUND EXPOSED PAD TO ENHANCE THERMAL PERFORMANCE Figure 4. Suggested Board Layout Switching Frequency IL 2A/DIV The switching frequency of the LT3479 is set by an external resistor attached to the RT pin. Do not leave this pin open.
PAGE 11
LT3479 APPLICATIONS INFORMATION Increasing switching frequency reduces output voltage ripple but also reduces efﬁciency. The user should set the frequency for the maximum tolerable output voltage ripple. Figure 8 shows a reduction in efﬁciency of about 4% between 1MHz and 2MHz operation in a typical application. Inrush Current Protection The LT3479 features a novel inductor current sensing circuit that protects the LT3479 during hot plugging and short circuits.
PAGE 12
LT3479 TYPICAL APPLICATIONS 5V to 12V/800mA 1MHz Boost Converter 90 D1 C1 2.2μF 200k VIN VS L SW FBN SHDN C2 10μF VOUT 12V 0.8A 80 23.2k LT3479 VREF SS RT GND 85 EFFICIENCY (%) VIN 5V L1 4.7μH Efﬁciency FBP VC 75 70 65 60 55 10nF 10k 17.8k 50 2.2nF 0 0.2 0.4 0.6 C1: TAIYO YUDEN LMK316BJ225MD C2: AVX 1206 YD106MAT D1: DIODES INC B320A L1: TOKO FDV0630-4R7M 3479 TA03b 5V to 12V/800mA 500kHz Boost Converter L1 10μH C1 2.2μF 90 D1 200k VIN VS L SW FBN SHDN 23.
PAGE 13
LT3479 TYPICAL APPLICATIONS 3.3V to 8V/900mA Boost Converter 90 D1 C1 2.2μF C2 10μF 169k VIN VS L SW FBN SHDN VOU 8V 0.9A 85 80 EFFICIENCY (%) VIN 3.3V L1 4.7μH Efﬁciency 30.9k LT3479 VREF SS RT GND FBP VC 75 70 65 60 55 4.3k 17.8k 10nF 50 10nF 0 0.2 0.4 0.6 C1: TAIYO YUDEN LMK316BJ225MD C2: AVX 1206 YD106MAT D1: DIODES INC B320A L1: TOKO FDV0630-4R7M 3479 TA03b 5V to –5V/600mA Inverting DC/DC Converter 90 C2 2.2μF D2 C1 2.
PAGE 14
LT3479 TYPICAL APPLICATIONS 500mA, 12 White LED Driver VIN 2.8V TO 4.2V L1 4.7μH D1 C1 2.2μF D2 600mA C2 2.2μF D3 VIN VS L SW ON M1 ON FBN SHDN SS LT3479 VREF 0.15Ω 124k FBP RT GND 10k VC 3479 TA07 10nF 7.5k 10k 2.
PAGE 15
LT3479 TYPICAL APPLICATIONS 500mA, 12 White LED Driver L1 10μH VOUT 16V TO 24V D1 C1 4.7μF C2 4.7μF D2 VIN VS L SW 100k FBN SHDN LT3479 SS VREF 93.1k FBP RT 5.9k VC GND 1Ω 10nF 1Ω 10k 17.8k ILED 500mA 3.3nF C1: TAIYO YUDEN EMK316BJ475ML C2: TAIYO YUDEN TMK325BJ475ML D1: DIODES INC B330B D2: LUMILEDS LXHL-NW99 L1: SUMIDA CDRH8D28-100 0.150Ω 3479 TA08 Efﬁciency 100 VIN = 16V VIN = 12V 90 EFFICIENCY (%) VIN 8V TO 16V VIN = 8V 80 70 60 50 0 0.1 0.2 0.3 IOUT (A) 0.4 0.
PAGE 16
LT3479 TYPICAL APPLICATIONS 8V, 16V, –8V Triple Output Power Supply for TFTLCD Panels D2B VIN 2.8V TO 4.2V C5 0.1μF L1 3.3μH D2A D1 C3 1μF 16V 10mA 8V 700mA C1 4.7μF 100k VIN VS L SW FBN C6 0.1μF SHDN LT3479 VREF GND FBP VC C2 22μF 18.7k SS 10nF RT D3A –8V 10mA 10k 17.8k C4 1μF D3B 2.
PAGE 17
LT3479 TYPICAL APPLICATIONS 1A Dual Tracking Power Supply with Adjustable Outputs 1μF 16V L1 15μH VIN 10V TO 14V 4.7μF 16V D1 VOUT 7V TO 10V 1A L2 15μH VIN VS L 30μF 16V 10.2k SW 470pF SHDN FBN SHDN LT3479 SS VCTRL 0V-2.5V 26.1k VREF 5.76k 1.13k FBP RT VC GND 10nF 4.99k 10.2k 10k 3.3nF 470pF 1μF 16V L3 15μH 4.7μF 16V L4 15μH 30μF 16V D2 VIN VS L SW FBN SHDN SS 11.3k VOUT –7V TO –10V 1A LT3479 VREF FBP RT 20nF GND VC D3 4.99k 10.2k 3.
PAGE 18
LT3479 PACKAGE DESCRIPTION DE Package 14-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1708 Rev B) 0.70 ±0.05 3.30 ±0.05 3.60 ±0.05 2.20 ±0.05 1.70 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 3.00 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.115 TYP 4.00 ±0.10 (2 SIDES) R = 0.05 TYP 3.00 ±0.10 (2 SIDES) 8 0.40 ± 0.10 14 3.30 ±0.10 1.70 ± 0.10 PIN 1 NOTCH R = 0.20 OR 0.
PAGE 19
LT3479 PACKAGE DESCRIPTION FE Package 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation BC 4.90 – 5.10* (.193 – .201) 3.58 (.141) 3.58 (.141) 16 1514 13 12 1110 6.60 p 0.10 9 2.94 (.116) 4.50 p 0.10 6.40 2.94 (.252) (.116) BSC SEE NOTE 4 0.45 p 0.05 1.05 p 0.10 0.65 BSC 1 2 3 4 5 6 7 8 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2.
PAGE 20
LT3479 TYPICAL APPLICATION Lumiled Driver for Photo Flash with Output Disconnnect VIN 3.3V TO 4.2V L1 4.7μH D1 C1 2.2μF VIN VS L ON C2 2.2μF D2 SW FBN D3 M1 SHDN LT3479 VREF 115k SS RT 10nF GND 7.5k FBP VC ON ILED 500mA/100mA 0.2Ω 2.49k 10k 10k TORCH MODE ILED = 100mA 2.