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LT3592

3592fc

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

500mA Wide Input Voltage

Range Step-Down LED Driver

with 10:1 Dimming

The LT

3592 is a ﬁ xed frequency step-down DC/DC con-

verter designed to operate as a constant-current source.

An external sense resistor monitors the output current

allowing accurate current regulation, ideal for driving

high current LEDs. The output current can be dimmed

by a factor of 10 using an external signal for nighttime

brake lights.

The high switching frequency offers several advantages by

permitting the use of a small inductor and small ceramic

capacitors. Small components combined with the LT3592’s

10-pin DFN leadless surface mount package save space and

cost versus alternative solutions. The constant switching

frequency combined with low-impedance ceramic capaci-

tors result in low, predictable output ripple.

A wide input voltage range of 3.6V to 36V makes the

LT3592 useful in a variety of applications. Current mode

PWM architecture provides fast transient response and

cycle-by-cycle current limiting. Thermal shutdown provides

additional protection.

50/500mA Two Series Red LED Driver

Wide Input Voltage Range

Operation from 3.6V to 36V

Resistor Adjustable 400kHz–2.2MHz Switching

Frequency

Shorted and Open LED Protected

Internal Switch Current Sense Resistor

External Resistor Programs LED Current, Pin

Selects 10:1 Ratio

50mA/500mA LED Current Settings

Catch Diode Current Sense to Prevent Runaway at

High V

Small Thermally Enhanced 10-Lead DFN

(2mm × 3mm) and MSOP-10 Packages

Automotive Signal Lighting

Industrial Lighting

Constant-Current, Constant Voltage Supplies

Efﬁ ciency for 2 Red LEDs, L = 10μH, 900kHz

10µH

51k

3592 TA01a

4.7µF

µF

0.4Ω

10k

0.1µF

SHDN

BRIGHT

BOOST

CAP

OUT

LT3592

GND

BRAKE

140k

900kHz

200/20mV

–

7V TO 32V

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

All other trademarks are the property of their respective owners.

INPUT VOLTAGE (V)

EFFICIENCY (%)

100

2012 24

3592 TA01b

28168

BRIGHT 500mA

Summary of content (24 pages)

PAGE 1
LT3592 500mA Wide Input Voltage Range Step-Down LED Driver with 10:1 Dimming DESCRIPTION FEATURES n n n n n n n n Wide Input Voltage Range Operation from 3.6V to 36V Resistor Adjustable 400kHz–2.
PAGE 2
LT3592 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN, BRIGHT Voltages ................................ –0.3V to 36V BOOST Voltage .........................................................60V BOOST above SW pin ...............................................30V CAP, OUT Voltages (OUT ≤ CAP) ...............................30V VFB Voltage .................................................................4V RT Voltage ...................................................................6V SHDN Voltage .................
PAGE 3
LT3592 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 12V, VBOOST = 16V, VOUT = 4V unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN TYP MAX 3.25 3.6 2 0.1 3 2 mA μA 190 18 200 20 210 22 mV mV –0.8 –1 –1.2 A 450 1000 2.5 kHz kHz MHz l Minimum Input Voltage Input Quiescent Current in Shutdown Not Switching VSHDN = 0.3V CAP to OUT Voltage 0.
PAGE 4
LT3592 TYPICAL PERFORMANCE CHARACTERISTICS Efﬁciency (2 Red LEDS, L = 10μH, 900kHz) (TA = 25°C, unless otherwise noted) Efﬁciency (1 Red LED, L = 6.
PAGE 5
LT3592 TYPICAL PERFORMANCE CHARACTERISTICS Undervoltage Lockout vs Temperature Switching Frequency vs Temperature 1400 RT = 48.7k 2100 1900 1700 3.3 fSW (kHz) UNDERVOLTAGE LOCKOUT (V) Current Limit During Soft Start 2300 SWITCH CURRENT LIMIT (mA) 3.4 3.2 1500 1300 1100 RT = 140k 900 700 500 3.1 –50 0 50 100 TEMPERATURE (°C) 300 –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (°C) 150 1000 800 600 400 0 0.5 3592 G11 SWITCH CURRENT LIMIT (A) 2000 1500 1000 500 1.50 1.3 1.45 1.2 1.
PAGE 6
LT3592 TYPICAL PERFORMANCE CHARACTERISTICS VBRIGHT vs VOUT (TA = 25°C, unless otherwise noted) VDIM vs VOUT 210 25 24 23 VBRIGHT (mV) VCAP – VOUT (mV) VCAP – VOUT (mV) 205 200 195 22 21 VDIM (mV) 20 19 18 17 16 190 0 2 4 6 8 15 12 10 VOUT (V) 0 2 4 6 VOUT (V) 8 3592 G18 Boost Diode Voltage vs Current Switching Frequency vs RT 3000 VBSTDIO 0.9 2500 FREQUENCY (kHz) DIODE FORWARD VOLTAGE (V) 12 3592 G19 1.0 0.8 0.7 0.6 0.5 0.
PAGE 7
LT3592 PIN FUNCTIONS RT (Pin 1): Programs the frequency of the internal oscillator. Connect a resistor from RT to ground. Refer to Table 1 or the Typical Performance Characteristics for resistor values that result in desired oscillator frequencies. BRIGHT (Pin 2): Used to program a 10:1 dimming ratio for the LED current. Drive this pin above 1.4V to command maximum intensity or below 0.3V to command minimum intensity.
PAGE 8
LT3592 BLOCK DIAGRAM L3 L2 BATT C2C C2B C2A 4 BRAKE VIN BRIGHT 2 RSENSE 9 LED1 R1 R2 10R – BOOST gm = 10 LED2 OUT + VFB – CAP 8 + R 6 R 1.
PAGE 9
LT3592 OPERATION The LT3592 is a constant frequency, current mode stepdown LED driver. An internal oscillator that is programmed by a resistor from the RT pin to ground enables an RS ﬂip-ﬂop, turning on the internal 1.25A power switch Q1. An ampliﬁer and comparator monitor the current ﬂowing between the VIN and SW pins, turning the switch off when this current reaches a level determined by the voltage at VC.
PAGE 10
LT3592 APPLICATIONS INFORMATION Oscillator The BRIGHT mode current is given by: The frequency of operation is programmed by an external resistor from RT to ground. Table 1 shows RT values for commonly used oscillator frequencies, and refer to the Typical Performance Characteristics curve for other values. Table 1. RT Values for Selector Oscillator Frequencies fOSC RT 400kHz 357k 900kHz 140k 2.2MHz 48.
PAGE 11
LT3592 APPLICATIONS INFORMATION (~0.4V at maximum load). This leads to a minimum input voltage of: VIN(MIN) = VOUT + VD – VD + VSW DCMAX Minimum On Time with DCMAX = 0.90. The maximum input voltage is determined by the absolute maximum ratings of the VIN and BOOST pins.
PAGE 12
LT3592 APPLICATIONS INFORMATION As the input voltage increases, the inductor current ramps up more quickly, the number of skipped pulses increases, and the output voltage ripple increases. For operation above VIN(MAX), the only component requirement is that they be adequately rated for operation at the intended voltage levels. The LT3592 is robust enough to survive prolonged operation under these conditions as long as the peak inductor current does not exceed 1.2A.
PAGE 13
LT3592 APPLICATIONS INFORMATION at the LT3592 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 1μF capacitor is capable of this task, but only if it is placed close to the LT3592 and catch diode (see the PCB layout section). A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT3592. A ceramic input capacitor combined with trace or cable inductance forms a high quality (underdamped) tank circuit.
PAGE 14
LT3592 APPLICATIONS INFORMATION VOUT ILED VSW C = 4.7μF 100μs/DIV VOUT ILED VSW C = 10μF 100μs/DIV 3592 F04 Figure 4. Transient Load Response of the LT3592 with Different Output Capacitors OPTIONAL BOOST D2 D2 BOOST C3 CAP LT3592 SW BATT C3 CAP LT3592 SW VIN BATT GND DA VIN GND DA 3592 F05a 3592 F05b (5a) (5b) Figure 5.
PAGE 15
LT3592 APPLICATIONS INFORMATION this restricts the input range to one-half of the absolute maximum rating of the BOOST pin. At light loads, the inductor current becomes discontinuous and the effective duty cycle can be very high. This reduces the minimum input voltage to about 400mV above VCAP. At higher load currents, the inductor current is continuous and the duty cycle is limited by the maximum duty cycle of the LT3592, requiring a higher input voltage to maintain regulation.
PAGE 16
LT3592 APPLICATIONS INFORMATION LT3592 RUN IL 500mA/DIV SHDN GND 3592 F07a VSW 10V/DIV VOUT 5V/DIV 50μs/DIV RUN 15k LT3592 IL 500mA/DIV SHDN 0.1μF GND VSW 10V/DIV 3592 F07b VOUT 5V/DIV 50μs/DIV Figure 7.
PAGE 17
LT3592 APPLICATIONS INFORMATION D4 VIN VIN VOUT SW LT3592 SHDN GND FB + BACKUP 3592 F08 D4: MBR0540 Figure 8. Circuit to Address Reversed Input and Backpowering Issues CLOSING SWITCH SIMULATES HOT PLUG IIN VIN LT3592 VIN + + GND IIN 10A/DIV 1μF VIN 20V/DIV LOW IMPEDANCE ENERGIZED 32V SUPPLY STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR 5μs/DIV (9a) VIN LT3592 + + + 10μF 50V GND IIN 10A/DIV 2.2μF VIN 20V/DIV 5μs/DIV (9b) 1Ω LT3592 VIN + + GND IIN 10A/DIV 0.1μF 2.
PAGE 18
LT3592 APPLICATIONS INFORMATION The small size, robustness, and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LT3592 circuits. However, these capacitors can cause problems if the LT3592 is plugged into a live supply (see Linear Technology Application Note 88 for a complete discussion).
PAGE 19
LT3592 APPLICATIONS INFORMATION two poles in the loop. Rc provides a zero. With the recommended output capacitor, the loop crossover occurs above the RCCC zero. This simple model works well as long as the value of the inductor is not too high and the loop crossover frequency is much lower than the switching frequency. With a larger ceramic capacitor that will have lower ESR, crossover may be lower and a phase lead capacitor (CPL) across the feedback divider may improve the transient response.
PAGE 20
LT3592 APPLICATIONS INFORMATION their maximum voltage capability. If a capacitor with a lower voltage rating is found to not be stable in a design, it will often result in a smaller solution to choose a larger capacitor value of the same voltage rating than to choose one of the same capacitance and higher voltage rating. For example, a 10μF, 10V ceramic capacitor might be smaller than a 4.7μF, 16V part, if a 4.7μF, 10V capacitor is found to not be adequate in a given application.
PAGE 21
LT3592 TYPICAL APPLICATIONS Single Red LED Driver with Boost Diode to VIN Due to Low VOUT 1N4148 VIN 5V TO 16V VIN 1μF BOOST 0.1μF 15μH LT3592 SW MBRA120 DA CAP SHDN OFF ON 0.4Ω BRIGHT FAULT 22μF OUT 30k RT GND 357k 400kHz LUXEON LXK2-PD12-S00 VFB 10k 3592 TA02 50mA/500mA Two Series Red LED Driver VIN 8V TO 32V BEAD 10μH VIN 10nF 3.3μF 1μF BOOST 0.1μF 6.8μH LT3592 SW CMMSHI-40 DA CAP SHDN OFF ON BRIGHT BRAKE OUT + 200/20mV – 4.7μF 0.4Ω 51k RT GND 48.7k 2.
PAGE 22
LT3592 PACKAGE DESCRIPTION DDB Package 10-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1722 Rev Ø) 0.64 ±0.05 (2 SIDES) 3.00 ±0.10 (2 SIDES) R = 0.05 TYP R = 0.115 TYP 6 0.40 ± 0.10 10 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.39 ±0.05 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.200 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 2.00 ±0.10 (2 SIDES) 0.75 ±0.05 0.64 ± 0.05 (2 SIDES) 5 0.25 ± 0.05 0 – 0.05 PIN 1 R = 0.20 OR 0.
PAGE 23
LT3592 PACKAGE DESCRIPTION MSE Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1664) BOTTOM VIEW OF EXPOSED PAD OPTION 2.794 p 0.102 (.110 p .004) 5.23 (.206) MIN 0.889 p 0.127 (.035 p .005) 1 0.05 REF 10 DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 3.00 p 0.102 (.118 p .004) (NOTE 3) 10 9 8 7 6 DETAIL “A” 0o – 6o TYP 1 2 3 4 5 GAUGE PLANE 0.53 p 0.152 (.021 p .006) DETAIL “A” 0.18 (.007) 0.497 p 0.076 (.0196 p .003) REF 3.
PAGE 24
LT3592 TYPICAL APPLICATIONS Five White LED Driver with External Booste Diode VIN 24V TO 36V VIN 1μF BOOST 0.1μF 33μH LT3592 BAS40 SW MBRA140 DA CAP OFF ON SHDN BRIGHT BRIGHT 0.4Ω 158k RT 140k 900kHz 4.7μF OUT GND VFB 10k WHITE LEDs 3592 TA05 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1932 Constant Current, 1.