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LTC3215

3215fc

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

700mA Low Noise High

Current LED Charge Pump

The LT C

3215 is a low noise, high current charge pump

DC/DC converter designed to power high current LEDs.

The part includes an accurate programmable current source

capable of driving loads up to 700mA from a 2.9V to 4.4V

input. Low external parts count (two flying capacitors, one

programming resistor and two bypass capacitors) makes

the LTC3215 ideally suited for small, battery-powered

applications.

Built-in soft-start circuitry prevents excessive inrush cur-

rent during start-up. High switching frequency enables

the use of small external capacitors. LED current is pro-

grammed with an external resistor. The LED is disconnected

from V

during shutdown.

An ultralow dropout current source maintains accurate

LED current at very low I

LED

voltages. Automatic mode

switching

optimizes efficiency by monitoring the voltage

across the LED current source and switching modes only

when I

LED

dropout is detected. The LTC3215 is available

in a low profile 3mm × 3mm 10-Lead DFN package.

Efficiency vs V

High Efficiency Operation: 1x, 1.5x or 2x Boost

Modes with Automatic Mode Switching

Ultralow Dropout I

LED

Current Control

Output Current up to 700mA

Low Noise Constant Frequency Operation*

Wide V

Range: 2.9V to 4.4V

Open/Shorted LED Protection

LED Disconnect in Shutdown

Low Shutdown Current: 2.5µA

4% LED Current Programming Accuracy

Automatic Soft-Start Limits Inrush Current

No Inductors

Tiny Application Circuit (All Components <1mm

Profile)

3mm × 3mm 10-Lead DFN Package

LED Torch/Camera Light Supply for Cell Phones,

PDAs and Digital Cameras

General Lighting and/or Flash/Strobe Applications

2.2µF

CPO

4.7µF

LED

200mA

LED1

LED

2.9V TO 4.4V

ENDISABLE ENABLE

LTC3215

–

SET

3215 TA01a

LED1: AOT2015

CPO

20k

(V)

2.8

EFFICIENCY (P

LED

) (%)

100

3.2

3.6

3.8

3215 TA01b

3.0 3.4

4.0

4.2

4.4

LED = AOT2015

= 3V TYP AT 200mA

LED

= 200mA

L, LT , LT C , LT M, Linear Technology and the Linear logo are registered trademarks of Linear

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

Protected by U.S. Patents, including 6411531.

Summary of content (14 pages)

PAGE 1
LTC3215 700mA Low Noise High Current LED Charge Pump FEATURES n n n n n n n n n n n n n DESCRIPTION High Efficiency Operation: 1x, 1.5x or 2x Boost Modes with Automatic Mode Switching Ultralow Dropout ILED Current Control Output Current up to 700mA Low Noise Constant Frequency Operation* Wide VIN Range: 2.9V to 4.4V Open/Shorted LED Protection LED Disconnect in Shutdown Low Shutdown Current: 2.
PAGE 2
LTC3215 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) VIN to GND................................................ –0.3V to 5.5V CPO to GND.............................................. –0.3V to 5.5V EN.................................................... –0.3V to VIN + 0.3V ICPO, IILED (Note 2)..............................................1000mA CPO Short-Circuit Duration............................... Indefinite Storage Temperature Range...................
PAGE 3
LTC3215 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, CIN = C1 = C2 = 2.2µF, CCPO = 4.7µF. PARAMETER CONDITIONS MIN TYP MAX UNITS CPO Short Circuit Detection Threshold Voltage EN = High ● 0.5 1.5 V Test Current EN = Low, VCPO = 0V ● 10 30 mA 1.4 EN High Level Input Voltage (VIH) ● Low Level Input Voltage (VIL) ● Input Current (IIH) ● Input Current (IIL) V 0.
PAGE 4
LTC3215 TYPICAL PERFORMANCE CHARACTERISTICS 1x Mode Charge Pump OpenLoop Output Resistance vs Temperature VIN = 3.6V VIN = 3.9V 0.25 0.23 0.21 0.19 0.17 1.6 1.8 1.4 1.6 1.2 1.0 0.8 0.6 VIN = 3V VCPO = 4.2V CIN = C1 = C2 = 2.2µF CCPO = 4.7µF 0.4 0.2 0.15 –40 –15 10 35 TEMPERATURE (°C) 60 0 –40 85 OUTPUT RESISTANCE (Ω) VIN = 3.3V –15 35 10 TEMPERATURE (°C) 1.2 1.0 0.8 0.6 0.4 Oscillator Frequency vs Supply Voltage 930 100 3.
PAGE 5
LTC3215 TYPICAL PERFORMANCE CHARACTERISTICS Charge Pump Mode Switching and Input Current (ILED = 400mA) (TA = 25°C unless otherwise specified) ISET/ILED Current Ratio vs ILED Current Efficiency vs VIN 100 3400 90 IVIN 500mA/ DIV EN2 5V/DIV VIN = 3V 1ms/DIV 3215 G12 3350 80 70 CURRENT RATIO EFFICIENCY (PLED/PIN) (%) VCPO 1V/DIV 60 50 40 30 20 10 0 100mA 200mA 400mA AOT2015 VF = 3V TYP AT 200mA 2.8 3.0 3.2 3.4 3.6 3.8 VIN (V) 3300 25°C 3250 –40°C 85°C 3200 3150 4.0 4.2 4.
PAGE 6
LTC3215 BLOCK DIAGRAM 2 10 C1+ 1 C1– 8 C2+ C2– CPO 3 1X MODE: CPO = VIN 1.5X MODE: CPO = 4.6V 2X MODE: CPO = 5.1V OSCILLATOR – + MODE CONTROL 7 6 VREF ILED DROPOUT DETECTOR 4 VIN EN CONTROL LOGIC CURRENT SOURCE CONTROL ISET GND 9 5 GND 11 3215 BD OPERATION The LTC3215 uses a fractional switched capacitor charge pump to power a high current LED with a programmed regulated current. The part starts up into the 1x mode. In this mode, VIN is directly connected to CPO.
PAGE 7
LTC3215 OPERATION Regulation is achieved by sensing the voltage at the CPO pin and modulating the charge pump strength based on the error signal. The CPO regulation voltages are set internally, and are dependent on the charge pump mode as shown in Table 1. ROL 1.5VIN OR 2VIN + + – CPO 3215 F01 – Table 1. Charge Pump Output Regulation Voltages CHARGE PUMP MODE VCPO 1.5x 4.6V 2x 5.1V In shutdown mode all circuitry is turned off and the LTC3215 draws a very low current from the VIN supply.
PAGE 8
LTC3215 OPERATION Mode Switching The LTC3215 will automatically switch from 1x mode to 1.5x mode, and subsequently from 1.5x mode to 2x mode whenever a dropout condition is detected at the ILED pin. The part will wait approximately 2ms before switching to the next mode. This delay allows the LED to warm up and reduce its forward voltage which may remove the dropout condition. 2.2µF C1+ µP VIO C1– C2+ 2.2µF C2– 2.9V TO 4.4V 4.7µF LTC3215 ILED EN VIO C1+ CPO 2.2µF ON/OFF TORCH/FLASH 2.
PAGE 9
LTC3215 APPLICATIONS INFORMATION VIN, CPO Capacitor Selection The value and type of capacitors used with the LTC3215 determine several important parameters such as regulator control loop stability, output ripple, charge pump strength and minimum start-up time. To reduce noise and ripple, it is recommended that low equivalent series resistance (ESR) ceramic capacitors be used for both CVIN and CCPO. Tantalum and aluminum capacitors are not recommended because of their high ESR.
PAGE 10
LTC3215 APPLICATIONS INFORMATION when comparing different capacitors, it is often more appropriate to compare the amount of achievable capacitance for a given case size rather than comparing the specified capacitance value. For example, over rated voltage and temperature conditions, a 1µF, 10V, Y5V ceramic capacitor in a 0603 case may not provide any more capacitance than a 0.22µF, 10V, X7R available in the same case.
PAGE 11
LTC3215 APPLICATIONS INFORMATION The efficiency of the LTC3215 depends upon the mode in which it is operating. Recall that the LTC3215 operates as a pass switch, connecting VIN to CPO, until dropout is detected at the ILED pin. This feature provides the optimum efficiency available for a given input voltage and LED forward voltage.
PAGE 12
LTC3215 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ±0.10 (4 SIDES) R = 0.125 TYP 6 0.40 ± 0.10 10 1.65 ± 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.
PAGE 13
LTC3215 REVISION HISTORY (Revision history begins at Rev C) REV DATE DESCRIPTION C 01/12 Revised titles on graphs G10-G14 in the Typical Performance Characteristics section PAGE NUMBER 4, 5 3215fc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 14
LTC3215 TYPICAL APPLICATION High Power Camera Light and Flash 2.2µF C1+ 2.9V TO 4.4V µP 2.8V 2.2µF C1– C2+ VIN C2– CPO 2.2µF 4.7µF LTC3215 ILED ON/OFF EN 2.8V TORCH/FLASH 30k 1% ILED 200mA/500mA ISET 10.5k 1% 3215 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1618 Constant Current, 1.4MHz, 1.5A Boost Converter VIN: 1.6V to 18V, VOUT(MAX) = 36V, IQ = 1.8mA, ISD < 1µA MS Package LT1961 1.5A (ISW), 1.