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LT3477

3477fc

TYPICAL APPLICATION

DESCRIPTION

3A, DC/DC Converter

with Dual Rail-to-Rail

Current Sense

FEATURES

APPLICATIONS

Dual 100mV Rail-to-Rail Current Sense Ampliﬁ ers

Wide Input Voltage Range: 2.5V to 25V

3A, 42V Internal Switch

High Efﬁ ciency Power Conversion: Up to 93%

Drives LEDs in Boost, Buck-Boost or Buck Mode

Frequency Set by External Resistor: 200kHz to 3.5MHz

Programmable Soft-Start

Low V

CESAT

Switch: 0.3V at 2.5A

Capable of Positive and Negative Output Voltages

(Boost, Inverting, SEPIC, Flyback)

Available in Thermally Enhanced 20-Lead

(4mm × 4mm) QFN and 20-Lead TSSOP Packages

The LT

3477 is a current mode, 3A DC/DC step-up con-

verter with dual rail-to-rail current sense ampliﬁ ers and an

internal 3A, 42V switch. It combines a traditional voltage

feedback loop and two unique current feedback loops to

operate as a constant-current, constant-voltage source.

Both current sense voltages are set at 100mV and can be

adjusted independently using the I

ADJ1

and I

ADJ2

pins. Ef-

ﬁ c i e n c y o f u p t o 9 1% c a n b e a c h i e v e d i n t y p i c a l a p p l i c a t i o n s .

The LT3477 features a programmable soft-start function

to limit inductor current during start-up. Both inputs of

the error ampliﬁ er are available externally allowing posi-

tive and negative output voltages (boost, inverting, SEPIC,

Flyback). The switching frequency is programmable from

200kHz to 3.5MHz through an external resistor.

Available in thermally enhanced 20-pin (4mm × 4mm)

QFN and 20-pin TSSOP packages, the LT3477 provides a

complete solution for both constant-voltage and constant-

current applications.

Efﬁ ciency

330mA LED Driver With Open LED Protection

SN1

SP1

ADJ1

ADJ2

FBN

SP2

200k

3.3μF

33nF

4.7nF

330mA

3477 TA01a

10k

22k

0.3Ω

10μH

FBP SSGND

LT3477

SN2

SHDN

REF

SHDN

OUT

(A)

EFFICIENCY (%)

0.4

3477 TA01b

0.1

0.2

0.3

High Power LED Driver

DSL Modems

Distributed Power

Input/Output Current Limited Boost, SEPIC,

Inverting, Flyback Converters

Constant-Voltage, Constant-Current Source

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

All other trademarks are the property of their respective owners.

Summary of content (20 pages)

PAGE 1
LT3477 3A, DC/DC Converter with Dual Rail-to-Rail Current Sense DESCRIPTION FEATURES n n n n n n n n n n Dual 100mV Rail-to-Rail Current Sense Ampliﬁers Wide Input Voltage Range: 2.5V to 25V 3A, 42V Internal Switch High Efﬁciency Power Conversion: Up to 93% Drives LEDs in Boost, Buck-Boost or Buck Mode Frequency Set by External Resistor: 200kHz to 3.5MHz Programmable Soft-Start Low VCESAT Switch: 0.3V at 2.
PAGE 2
LT3477 ABSOLUTE MAXIMUM RATINGS (Note 1) SW Pin Voltage ........................................................ 42V VIN, SHDN Pin Voltage ............................................. 25V FBP, FBN Pin Voltage ................................................. 6V VREF Pin Voltage......................................................... 6V RT, VC , SS Pin Voltage ............................................... 6V IADJ1, IADJ2 Pin Voltage ............................................
PAGE 3
LT3477 ELECTRICAL CHARACTERISTICS The ● indicates 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 Maximum VREF Pin Current Out of Pin Soft-Start Pin Current SS = 0.
PAGE 4
LT3477 TYPICAL PERFORMANCE CHARACTERISTICS SHDN Pin Turn-On Threshold SHDN Pin Current Quiescent Current 50 1.6 6 VC = 0.3V 1.4 1.2 40 QUIESCENT CURRENT (mA) SHDN PIN CURRENT (μA) SHDN THRESHOLD (V) –50°C 30 25°C 20 125°C 10 1.0 –50 0 50 25 75 0 TEMPERATURE (°C) –25 100 125 5 0 15 10 VSHDN (V) 20 4 3 2 –50 –25 25 Soft-Start Pin Current 25 50 75 100 125 150 TEMPERATURE (°C) 3477 G06 Oscillator Frequency 20 Feedback Ampliﬁer Offset Voltage 2.0 4 1.
PAGE 5
LT3477 TYPICAL PERFORMANCE CHARACTERISTICS Current Sense Voltage vs Temperature Current Sense Voltage vs IADJ 120 103 101 VCM = 10V 100 99 VCM = 42V 98 80 60 40 20 97 96 –50 –25 VCM = 10V 100 102 VOLTAGE SENSE (mV) CURRENT SENSE VOLTAGE (mV) 104 0 50 75 25 TEMPERATURE (°C) 100 125 3477 G14 0 0 100 200 300 400 500 600 700 800 IADJ VOLTAGE (mV) 2477 G13 PIN FUNCTIONS (QFN/TSSOP) NC (Pins 1, 2, 20/Pins 18, 19, 20): No Connect Pin. Okay to connect to ground or VIN, or to ﬂoat.
PAGE 6
LT3477 PIN FUNCTIONS (QFN/TSSOP) ISP2 (Pin 13/Pin 11): Second Current Sense (+) Pin. The noninverting input to the second current sense ampliﬁer. Connect to ISN2 if not used. ISN2 (Pin 14/Pin 12): Second Current Sense (–) Pin. The inverting input to the second current sense ampliﬁer. Connect to ISP2 if not used. ISP1 (Pin 15/Pin 13): First Current Sense (+) Pin. The noninverting input to the ﬁrst current sense ampliﬁer. Connect to ISN1 if not used. GND (Pins 17/Pin 15): Ground.
PAGE 7
LT3477 OPERATION The LT3477 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 in Figure 1. The start of each oscillator cycle sets the SR latch and turns on power switch Q1. The signal at the noninverting input of the PWM comparator (A4 SLOPE) is proportional to the sum of the switch current and oscillator ramp.
PAGE 8
LT3477 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
LT3477 APPLICATIONS INFORMATION Setting Positive Output Voltages To set a positive output voltage, select the values of R1 and R2 (see Figure 2) according to the following equation: R1 VOUT =1.235V 1+ R2 FBP LT3477 VOUT For designs needing an adjustable current level, the IADJ1 and IADJ2 pins are provided for the ﬁrst and the second current sense ampliﬁers, respectively.
PAGE 10
LT3477 APPLICATIONS INFORMATION some tweaking of the compensation values (RC and CC on the VC pin) may be required to ensure a clean inductor ripple current while the constant-current loop is in effect. For these applications, the constant-current loop response can usually be improved by reducing the RC value or by adding a capacitor (with a value of approximately CC/10) in parallel with the RC and CC compensation network.
PAGE 11
LT3477 APPLICATIONS INFORMATION PWM Dimming For LED applications where a wide dimming range is required, two competing methods are available: analog dimming and PWM dimming. The easiest method is to simply vary the DC current through the LED—analog dimming—but changing LED current also changes its chromaticity, undesirable in many applications. The better method is PWM dimming, which switches the LED on and off, using the duty cycle to control the average current.
PAGE 12
LT3477 APPLICATIONS INFORMATION VIN 5V L1 2.0μH C1 3.3μF ISP1 D1 C2 10μF 1M SW ISN1 VIN IADJ1 IADJ2 SHDN OUT FBN 75k FBP LT3477 VREF ISP2 SS CSS 33nF RSENSE 0.33Ω ISN2 LED1 RT VC GND LED2 6.81k D2 PWM 5V 300mA LED3 NMOS1 0 LED4 RC 2.
PAGE 13
LT3477 APPLICATIONS INFORMATION PVIN 32V C1 2.2μF RSENSE 0.33Ω 300mA C1: NIPPON NTS40X5R1H225M C2: TAIYO YUDEN GMK316BJ105ML C3: TAIYO YUDEN LMK316BJ335KL L1: TOKO D53LC (PN# A915AY-100M) D1: ZETEX ZLLS400 D2: DIODES INC 1N4148 NMOS1, NM0S2: ZETEX 2N7002 PMOS: SILICONIX Si2303BDS LED1 TO LED6: LUMILEDS LXHL-BW02 LED1 • • • LED6 1k PMOS NMOS2 PWM C2 1μF L1 10μH ISP1 VIN 3.3V 1k ISN1 280k SW VIN IADJ1 IADJ2 C3 3.
PAGE 14
LT3477 APPLICATIONS INFORMATION 1k C1: TAIYO YUDEN LMK316BJ335ML C2: TAIYO YUDEN UDK325BJ106MM L1: TOKO D53LC (PN# A915AY-4R7M) D1: ZETEX ZLLS1000 D2: DIODES INC 1N4148 NMOS1, NMOS2: ZETEX 2N7002 PMOS: SILICONIX Si2303BDS LED1, LED2: LUMILEDS LXHL-BW02 NMOS2 PWM 1k LED2 PMOS VIN 10V C1 3.3μF ISP1 L1 4.7μH ISN1 RSENSE 0.33Ω D1 1M SW VIN IADJ1 IADJ2 300mA LED1 FBN 49.9k FBP SHDN VREF LT3477 ISP2 SS CSS 33nF ISN2 VC D2 5V PWM RT GND 6.81k C2 10μF 3477 F09a NMOS1 0 100Hz 100k RC 1.
PAGE 15
LT3477 TYPICAL APPLICATIONS Efﬁciency 5.5V SEPIC Converter With Short-Circuit Protection C1 3.3μF ISP1 ISN1 SHDN FBN SHDN LT3477 VIN = 3V 85 5.5V 670mA R4 34.8k L2 4.7μH SW VIN IADJ1 IADJ2 R3 0.15Ω D1 80 EFFICIENCY (%) VIN 3V TO 16V 90 C2 10μF L1 4.7μH R1 0.04Ω ISP2 75 70 65 60 55 VC ISN2 VREF RC 1k 50 RT FBP GND 0 0.1 0.2 SS C4 33nF CC 4.7nF C3 10μF R2 18.2k 0.3 0.4 IOUT (A) 0.5 0.6 0.
PAGE 16
LT3477 TYPICAL APPLICATIONS 87% Efﬁcient, 4W LED Driver R4 L2 0.05Ω 10μH C1 3.3μF ISP1 ISN1 SW FBN R1 10k SHDN LT3477 ISP2 85 C2 3.3μF R2 200k VIN IADJ1 IADJ2 SHDN 90 D1 330mA 80 EFFICIENCY (%) VIN 5V Efﬁciency R6 0.3Ω VREF RC 1k FBP GND SS 50 LED2 C3 33nF CC 4.7nF 0 0.1 0.2 0.4 0.3 IOUT (A) LED3 R3 22k C1: TAIYO YUDEN LMK316BJ335ML C2: TAIYO YUDEN TMK325BJ335MN D1: DIODES INC.
PAGE 17
LT3477 TYPICAL APPLICATIONS Buck-Boost Mode LED Driver LED2 LED1 L1 4.7μH VIN 2.7V TO 10V C1 3.3μF ISP1 ISN1 SHDN SHDN R3 200k SW1 VIN IADJ1 IADJ2 LED BRIGHTNESS CONTROL 0mV TO 650mV R1 0.1Ω D1 FBN LT3477 ISP2 ISN2 VC VREF FBP RT GND SS C3 33nF CC 10nF R2 18k R4 10k C1: TAIYO YUDEN LMK316BJ335ML C2: MURATA GRM31CR71E475KA88L D1: DIODES, INC. B320A L1: TOKO FDV0630-4R7M C2 4.7μF 3477 TA06a Efﬁciency 90 85 VIN = 8V EFFICIENCY (%) 80 75 VIN = 4.2V 70 65 VIN (V) IOUT (A) 2.7 3.
PAGE 18
LT3477 PACKAGE DESCRIPTION UF Package 20-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1710) 0.70 ±0.05 4.50 ± 0.05 3.10 ± 0.05 2.45 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS BOTTOM VIEW—EXPOSED PAD 4.00 ± 0.10 (4 SIDES) 0.75 ± 0.05 R = 0.115 TYP PIN 1 NOTCH R = 0.30 TYP 19 20 0.38 ± 0.10 PIN 1 TOP MARK (NOTE 6) 1 2 2.45 ± 0.10 (4-SIDES) (UF20) QFN 10-04 0.200 REF 0.00 – 0.05 0.25 ± 0.05 0.50 BSC NOTE: 1.
PAGE 19
LT3477 PACKAGE DESCRIPTION FE Package 20-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation CB 6.40 – 6.60* (.252 – .260) 3.86 (.152) 3.86 (.152) 20 1918 17 16 15 14 13 12 11 6.60 ±0.10 2.74 (.108) 4.50 ±0.10 6.40 2.74 (.252) (.108) BSC SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 9 10 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.25 REF 0.50 – 0.75 (.020 – .030) NOTE: 1.
PAGE 20
LT3477 TYPICAL APPLICATION Buck Mode High Current LED Driver PVIN 32V C1 2.2μF R1 0.1Ω Efﬁciency LED1 • • • 1A LED4 LED STRING C2 1μF 100 90 80 ISP1 VIN 3.3V ISN1 SHDN SHDN FBN LT3477 50 20 ISN2 FBP 60 30 ISP2 VREF 70 40 R4 10k VC RC 1k R3 280k SW VIN IADJ1 IADJ2 C3 3.3μF EFFICIENCY (%) L1 33μH D1 0 0.2 0.4 0.6 LED CURRENT (A) 0.8 1 3477 TA05b RT GND CC 4.