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LTC3490

3490fa

■

Portable Lighting

■

Rechargeable Flashlights

Single Cell Minimum Component LED Driver

Single Cell 350mA

LED Driver

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350mA Constant Current Output

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2.8V to 4V Output Compliance

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1- or 2-Cell NiMH or Alkaline Input

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Synchronous Rectification: Up to 90% Efficiency

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Fixed Frequency Operation: 1.3MHz

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Low Quiescent Current: <1mA

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Very Low Shutdown Current: <50µA

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Open LED Output Limited to 4.7V

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Range: 1V to 3.2V

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Dimming Control

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Undervoltage Lockout to Protect Batteries

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Low Profile (0.75mm) 3mm × 3mm Thermally

Enhanced 8-Lead DD and S8 Packages

Efficiency vs V

at V

LED

= 3.5V

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

The LTC

3490 provides a constant current drive for 1W

LED applications. It is a high efficiency boost converter

that operates from 1 or 2 NiMH or alkaline cells and

generates 350mA of constant current with up to 4V of

compliance. It contains a 100mΩ NFET switch and a

130mΩ PFET synchronous rectifier. The fixed switching

frequency is internally set to 1.3MHz.

The LTC3490 limits the output voltage to 4.7V if the output

load is disconnected. It also features an analog dimming

capability that reduces the drive current proportional to

the CTRL/SHDN pin voltage. A low-battery logic output

signals when the battery has dropped below 1V/cell. An

undervoltage lockout circuit shuts down the LTC3490

when the battery voltage drops below 0.85V/cell. The

feedback loop is internally compensated to minimize com-

ponent count.

CAP

ON/OFF

LED

1 NiMH OR

ALKALINE

CELL

4.7µF

LOBAT

3490 TA01

CTRL/SHDN

CELLS

HIGH

CURRENT

LED

GND

LTC3490

3.3µH

350mA

(V)

EFFICIENCY (%)

100

1.5

3490 TA02

2.5

OUT

= 350mA

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

All other trademarks are the property of their respective owners.

Summary of content (12 pages)

PAGE 1
LTC3490 Single Cell 350mA LED Driver U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO 350mA Constant Current Output 2.8V to 4V Output Compliance 1- or 2-Cell NiMH or Alkaline Input Synchronous Rectification: Up to 90% Efficiency Fixed Frequency Operation: 1.3MHz Low Quiescent Current: <1mA Very Low Shutdown Current: <50µA Open LED Output Limited to 4.7V VIN Range: 1V to 3.2V Dimming Control Undervoltage Lockout to Protect Batteries Low Profile (0.
PAGE 2
LTC3490 W W W AXI U U ABSOLUTE RATI GS (Note 1) Supply Voltage (VIN) ................................... – 0.3V to 6V Input Voltages (CTRL/SHDN, CELLS) ......... – 0.3V to 6V Output Voltages (CAP, LED, SW) ................ – 0.3V to 6V Operating Temperature Range (Note 2) .. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 125°C Lead Temperature (Soldering, 10 sec, S8) ..........
PAGE 3
LTC3490 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VIN = 2.5V unless otherwise specified. SYMBOL IL(PMOS) PARAMETER Leakage Current, PMOS Switch RON(PMOS) On-Resistance, PMOS Switch VIH Input High (CELLS) CONDITIONS MIN MAX UNITS µA Ω 0.13 VIN – 0.4 Input High (SHDN) VIL TYP 0.1 V VIN • 0.9 Input Low (CELLS) V 0.4 Input Low (SHDN) V VIN • 0.2 V 0.
PAGE 4
LTC3490 U W TYPICAL PERFOR A CE CHARACTERISTICS ILED vs VLED 360 Efficiency vs ILED 100 VIN = 2.4V 358 356 80 EFFICIENCY (%) 354 ILED (mA) VIN = 2.4V 90 352 350 348 50 40 346 30 344 20 342 10 340 VIN = 1.2V 70 60 0 3 2.8 3.2 3.4 3.6 VLED (V) 3.8 4 3490 G04 0 100 200 ILED (mA) 400 300 3490 G05 U U U PI FU CTIO S CELLS (Pin 1): A logic input to set the low-battery and undervoltage shutdown thresholds. A logic low (tied to GND) will set the thresholds for 1 cell.
PAGE 5
LTC3490 W FU CTIO AL DIAGRA U 3 SW – 2 P BODY CONTROL + VIN CAP 6 GATE CONTROL AND DRIVERS SENSE AMP LIMIT 19.2Ω + – OVERVOLTAGE DETECT LED 5 250k – PWM LOGIC 0.
PAGE 6
LTC3490 U OPERATIO The LTC3490 is a high efficiency, constant current source for 1W high intensity white LEDs. These high intensity LEDs require a fixed current of 350mA with a voltage compliance of 2.8V to 4V. The LTC3490 operates with 1 or 2 NiMH or alkaline cells. It functions as a boost converter with a current sense resistor providing the control feedback. If the battery voltage is greater than the required LED compliance, it will cycle off periodically to maintain the correct average current.
PAGE 7
LTC3490 U W U U APPLICATIO S I FOR ATIO The LTC3490 requires only four external components to operate: an inductor, an output capacitor, a switch and a pull-down resistor. The inductor is nominally set at 3.3µH and the capacitor at 4.7µF. Optional components include an input capacitor and dimming resistors.
PAGE 8
LTC3490 U W U U APPLICATIO S I FOR ATIO The output ripple voltage has two primary components. The first is due to the value of the capacitor and is given by: VRCAP = ILPK • VIN C • VOUT • f The second is due to the capacitor ESR: VRESR = ILPK • RESR Component values will be calculated for 1 or 2 NiMH cells and assumes the end-of-charge voltage to be 0.9V per cell. The operating frequency is assumed to be 1MHz, the worst-case low frequency. The allowed inductor ripple current is 0.31A.
PAGE 9
LTC3490 U W U U APPLICATIO S I FOR ATIO Red Luxeon LEDs is only 2.31V. The LTC3490 requires an additional 190mV for proper operation. In non-dimming applications, this can be accomplished with a 0.6Ω resistor in series with the LED. The resistor voltage drops too low in dimming applications, so a Schottky diode is recommended to keep sufficient voltage at the output at lower currents. The red, red-orange and amber Luxeon LEDs have a lower forward voltage than the white, blue and green LEDs.
PAGE 10
LTC3490 U TYPICAL APPLICATIO S Luxeon Red LED Driver Without Dimming 3.3µH ON/OFF SW VIN CAP 1 NiMH OR ALKALINE CELL LTC3490 + 4.7µF CTRL/SHDN LED 0.6Ω LOBAT CELLS 1M LUMILEDS LUXEON LXHL-BD03 GND 3490 TA06 Luxeon Red LED Driver with Dimming 3.3µH ON/OFF SW VIN CAP 1 NiMH OR ALKALINE CELL LTC3490 + 4.
PAGE 11
LTC3490 U PACKAGE DESCRIPTIO DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698) R = 0.115 TYP 5 0.38 ± 0.10 8 0.675 ±0.05 3.5 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) PACKAGE OUTLINE 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (NOTE 6) (DD8) DFN 1203 0.25 ± 0.05 4 0.25 ± 0.05 0.75 ±0.05 0.200 REF 0.50 BSC 2.38 ±0.05 (2 SIDES) 1 0.50 BSC 2.38 ±0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1.
PAGE 12
LTC3490 U TYPICAL APPLICATIO LED Driver Drops to 20% Amplitude on Low-Battery Detect 3.3µH ON/OFF VIN SW CAP 1 NiMH OR ALKALINE CELL + LTC3490 1M 350mA/70mA CTRL/SHDN LED CELLS 1M 432k LOBAT GND 4.7µF LUMILEDS LUXEON LXHL-BWO2 3490 TA05 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT 1618 Constant Current, Constant Voltage 1.4MHz, High Efficiency Boost Regulator VIN: 1.6V to 18V, VOUT(MAX) = 34V, IQ = 1.8mA, ISD < 1µA, MS/EDD Packages LT1932 Constant Current, 1.