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LTC3454

3454fa

LED Power Efﬁ ciency vs V

TYPICAL APPLICATION

DESCRIPTION

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

All other trademarks are the property of their respective owners.

FEATURES

APPLICATIONS

The LTC

3454 is a synchronous buck-boost DC/DC

converter optimized for driving a single high power LED

at currents up to 1A from a single cell Li-Ion battery in-

put. The regulator operates in either synchronous buck,

synchronous boost, or buck-boost mode depending on

input voltage and LED forward voltage. P

LED

efﬁ ciency

greater than 90% can be achieved over the entire usable

range of a Li-Ion battery (2.7V to 4.2V).

LED current is programmable to one of four levels, includ-

ing shutdown, with dual external resistors and dual enable

inputs. In shutdown no supply current is drawn.

A high constant operating frequency of 1MHz allows the

use of small external components. The LTC3454 is offered

in a low proﬁ le (0.75mm) thermally enhanced 10-lead

(3mm × 3mm) DFN package.

Cell Phone Camera Flash

Cell Phone Torch Lighting

Digital Cameras

PDAs

Misc Li-Ion LED Drivers

High Efﬁ ciency: >90% Typical in Torch Mode,

>80% in Flash Mode

Wide V

Range: 2.7V to 5.5V

Up to 1A Continuous Output Current

3.5% LED Current Programming Accuracy

Internal Soft-Start

Open/Shorted LED Protection

Constant Frequency 1MHz Operation

Zero Shutdown Current

Overtemperature Protection

Small Thermally Enhanced 10-Lead (3mm × 3mm)

DFN Package

High Efﬁ ciency Torch/Flash LED Driver

LED

ISET1

20.5k

3454 TA01a

ISET2

3.65k

EN2 (FLASH)

EN1 (TORCH)

EN2 EN1 I

LED

0 0 0 (SHUTDOWN)

0 1 150mA

1 0 850mA

111A

0.1μF

GND (EXPOSED PAD)

LTC3454

LED: LUMILEDS LXL-PWF1

L1: SUMIDA CDRH6D28-5RONC

SW1

SW2

10μF

2.7V TO 4.2V

1-CELL Li-Ion

OUT

10μF

5μH

1MHz

BUCK-BOOST

LED

SET1

SET2

(V)

2.7

EFFICIENCY (%)

4.3

5.55.1

3454 TA01b

3.1 3.93.5 4.7

100

LED

= 150mA

LED

= 1A

= 25°C

EFFICIENCY = (V

OUT

– V

LED

1A Synchronous Buck-Boost

High Current LED Driver

Summary of content (12 pages)

PAGE 1
LTC3454 1A Synchronous Buck-Boost High Current LED Driver FEATURES DESCRIPTION n The LTC®3454 is a synchronous buck-boost DC/DC converter optimized for driving a single high power LED at currents up to 1A from a single cell Li-Ion battery input. The regulator operates in either synchronous buck, synchronous boost, or buck-boost mode depending on input voltage and LED forward voltage. PLED/PIN efﬁciency greater than 90% can be achieved over the entire usable range of a Li-Ion battery (2.7V to 4.2V).
PAGE 2
LTC3454 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) VIN, SW1, SW2, VOUT Voltage ...................... –0.3V to 6V VC, EN1, EN2, ISET1, ISET2 Voltage.............................–0.3V to (VIN + 0.3V) or 6V LED Peak Current ...................................................1.25A Storage Temperature Range...................–65°C to 125°C Operating Temperature Range (Note 2)....–40°C to 85°C Junction Temperature (Note 3) .............................
PAGE 3
LTC3454 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 3.6V, RISET = 20.5k unless otherwise noted. (Note 2) PARAMETER CONDITIONS Oscillator Frequency MIN TYP MAX UNITS 0.9 1.0 1.15 MHz Soft-Start Time 200 Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device.
PAGE 4
LTC3454 TYPICAL PERFORMANCE CHARACTERISTICS LED Current Programming Ratio vs VIN 4050 VIN = 3.6V 4000 4000 3950 3950 3900 3900 RATIO RATIO 4050 3850 3800 150 PROGRAMMED ILED = 500mA TA = 25°C PROGRAMMED ILED = 1A 3850 90 PROGRAMMED ILED = 500mA 60 3750 3650 –55 –35 –15 30 PROGRAMMED ILED = 1A PROGRAMMED ILED = 500mA PROGRAMMED ILED = 150mA 3700 PROGRAMMED ILED = 100mA 3700 5 25 45 65 85 105 125 TEMPERATURE (°C) 3650 2.7 3.1 3.5 3.9 4.3 VIN (V) 4.7 3454 G07 5.
PAGE 5
LTC3454 TYPICAL PERFORMANCE CHARACTERISTICS Oscillator Frequency vs Temperature 1080 100 VOUT = 3V 95 FREQUENCY (kHz) 1060 VIN = 5.5V 1040 VIN = 4.2V 1020 1000 VIN = 2.7V 980 VIN = 3.6V 960 90 EFFICIENCY (%) 1100 LED Power Efﬁciency vs LED Current 85 80 75 70 940 920 900 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) VIN = 3.
PAGE 6
LTC3454 BLOCK DIAGRAM OPTIONAL 10 SW1 SWITCH A GATE DRIVERS AND ANTICROSSCONDUCTION SWITCH B UNDERVOLTAGE LOCKOUT UV 7 REVERSE CURRENT LIMIT OT BANDGAP REFERENCE – – 3.4A 275mA 1.23V LOGIC + – – AB PWM COMPARATOR CD PWM COMPARATOR UV 8 VOUT SWITCH D SWITCH C FORWARD CURRENT LIMIT + OVERTEMP PROTECTION 6 SW2 + 9 VIN + VIN 2.7V TO 5.5V OPTIONAL OT 1MHz OSCILLATOR VC VOUT 1.23V – SAFETY ERROR AMP AUTOZEROING ERROR AMP LED – 5 377k R + + 123k SOFTSTART CLAMP 1.
PAGE 7
LTC3454 OPERATION Buck-Boost DC/DC Converter The LTC3454 employs an LTC proprietary buck-boost DC/DC converter to generate the output voltage required to drive a high current LED. This architecture permits highefﬁciency, low noise operation at input voltages above, below or equal to the output voltage by properly phasing four internal power switches. The error amp output voltage on the VC pin determines the duty cycle of the switches.
PAGE 8
LTC3454 APPLICATIONS INFORMATION Boost Mode (VIN < VOUT) In boost mode, switch A is always on and switch B is always off. Referring to Figure 2, when the control voltage VC is above voltage V3, switches C and D will alternate conducting similar to a typical synchronous boost regulator. The maximum duty cycle of the converter is limited to 88% typical and is reached when VC is above V4. Forward Current Limit If the current delivered from VIN through PMOS switch A exceeds 3.
PAGE 9
LTC3454 APPLICATIONS INFORMATION COMPONENT SELECTION Inductor Selection The high frequency operation of the LTC3454 allows the use of small surface mount inductors. The inductor current ripple is typically set to 20% to 40% of the maximum average inductor current.
PAGE 10
LTC3454 TYPICAL APPLICATIONS diode such as an MBRM120T3 or equivalent. Do not use ordinary rectiﬁer diodes, since the slow recovery times will compromise efﬁciency. and slower transient response. To ensure proper phase margin, the loop is required to be crossed over a decade before the LC double pole.
PAGE 11
LTC3454 APPLICATIONS INFORMATION LED Failure Modes If the LED fails as an open circuit, the safety ampliﬁer takes control of the regulation loop to prevent VOUT runaway. The VOUT threshold at which this occurs is about 5.15V. The safety ampliﬁer has no effect on loop regulation at VOUT less than 5.15V. VIN If the LED fails as a short-circuit, the current limiting circuitry detects this condition and limits the peak input current to a safe level.
PAGE 12
LTC3454 TYPICAL APPLICATION 500mA LED Flashlight Driver L1 4.7μH 3-CELL ALKALINE 4.5V VIN 2.2μF LED Power Efﬁciency vs VIN SW2 SW1 VOUT 4.7μF 100 ILED = 500mA 95 EN1 SWD SWB LED 90 EFFICIENCY (%) SWA LED SWC EN2 VC 80 75 70 1MHz BUCK-BOOST ISET1 ISET2 0.1μF LTC3454 GND (EXPOSED PAD) LED: LUMILEDS, LXCL LW3C L1: TOKO A997AS-4R7M 85 RISET1 6.19k 1% 3453 TA02 65 ILED = 500mA TA = 25°C EFFICIENCY = (VOUT – VLED)ILED/VINIIN 60 2.7 3.1 3.5 3.9 4.3 VIN (V) 4.7 5.5 5.