National Semiconductor LM2754 Technical data

LM2754 800mA Switched Capacitor Flash LED Driver with Time-Out Protection

September 2006

General Description

The LM2754 is an integrated low noise, high current switched capacitor DC/DC converter with four regulated current sinks. The device is optimized for driving 1 to 4 high power white LEDs in parallel with a maximum current of 800mA. Maximum efficiency is achieved over the input voltage range by actively selecting the proper gain based on the LED forward voltage and current requirements.

Two external low power resistors set the desired current for Torch and Flash modes. The TX pin allows the device to be forced into Torch mode during a Flash pulse, allowing for synchronization between the RF power amplifier pulse and Flash/Torch modes. To protect the device and Flash LEDs, internal Time-Out circuitry turns off the LM2754 in case of a faulty prolonged Flash mode. Internal soft-start circuitry limits the amount of inrush current during start-up.

The LM2754 is available in a small 24-pin thermally enhanced LLP package.

Features

n Up to 800mA Output Current n Wide Operating Input Voltage Range: 2.8V to 5.5V n Drives 1, 2, 3 or 4 LEDs in Parallel n Ability to Disable One Current Sink Via the SEL Pin to

Accommodate 3-LED Flash Modules

n Time-Out Circuitry Limits Flash Duration to 1 Second n TX Input Ensures Synchronization with RF Power

Amplifier Pulse

n Adaptive 1x, 1.5x and 2x Gains for Maximum Efficiency n 1MHz Constant Frequency Operation n Output Current Limit n True Shutdown Output Disconnect

1µA Shutdown Current

n Internal Soft-Start Limits Inrush Current n No Inductor Required n Total Solution Size without LED n Low Profile 24-Pin LLP Package (4mm x 4mm x 0.8mm)

28mm

Applications

n Camera Flash in Mobile Phones n Flash for Digital Cameras n Supplies for DSP’s, Microprocessors, Memory, MP3

Players, Pagers, Other Portable Devices

Typical Application Circuit

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Connection Diagram

LM2754

Pin Descriptions

Pin Name Description

23,24 V

22 V

12, 13, 14, 15 D1, D2, D3, D4* Regulated Current Sink Inputs. (* See SEL PIN description)

1, 2, 7, 5 C

3 GND

9, 16, 17 GND Ground Connection. Connect GND and GND

21 EN Enable Control Pin. Logic High = Normal Operation in Torch Mode.

20 T/F Torch/Flash Control Pin. Logic High = Flash Mode. Logic Low = Torch Mode.

10, 11 I

19 TX RF PA synchronization control pin. Logic High = Force Torch Mode. Logic Low

18 SEL D

4, 6 No Connect Do not connect to any node.

Note: EN, T/F, TX, and SEL pins each have a 500kΩ resistor connected internally to GND

LM2754

24-pin No-Pullback Leadless Leadframe Package (LLP-24)

4mm x 4mm x 0.8mm

NS Package Number SQA24A

INSW

Input Voltage Connection for Switch Array. Pins 23 and 24 are connected internally on the die. Connect V

OUT

+, C1-, C2+, C2- Flying Capacitor Connections.

Input Voltage Connection. Connect VINand V

Output Voltage. Connect to LED Anodes.

Switch Array Ground Connection. Connect GND and GNDSWpins together.

Logic Low = Device Shut-Down. (See Note)

Device must be enabled for Torch or Flash to operate. (See Note)

SET1,ISET2

Current Set Resistor Connections. Connect 1% resistors to ground to set the desired current through the LEDs. LED current is approximated by the equation: 800 x (1.25V ÷ R). This equation corresponds to the current through one current sink. Total LED current is equal to the sum of currents through all current sinks connected to the LED. The equation used for Torch (I Flash (I

) resistors are the same.

SET2

= Normal Operation. (See Applications Information section for the full operational description) (See Note)

Control Pin. Logic Low = Normal 4-LED Operation. Logic High = Disable

LED Input. Connect D4to V

and V

when not used. (See Note)

OUT

pins together.

INSW

pins together.

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SET1

) and

Ordering Information

Order Number Package Description Package Marking Supplied as Tape and Reel

LM2754SQ No-Pullback

LM2754SQX 4500

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LLP-24

UZXYTT

LM2754

(Units)

1000

LM2754

Absolute Maximum Ratings (Notes 1, 2)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

IN,VOUT

EN, T/F, TX, SEL pins -0.3V to (V

pins -0.3V to 6.0V

+ 0.3V)

Operating Ratings (Notes 1, 2)

Input Voltage (V

Junction Temperature Range (T

Ambient Temperature Range (T (Note 5) -40˚C to +85 ˚C

) 2.8V to 5.5V

) -40˚C to +125˚C

)

w/ 6.0V max

Continuous Power Dissipation (Note 3) Internally Limited

Junction Temperature (T

J-MAX-ABS

) 150˚C

Thermal Information

Junction-to-Ambient Thermal Resistance, LLP-24 Package (θ

) (Note 6) 42˚C/W

Storage Temperature Range -65˚C to 150˚C

Lead Temp. (Soldering, 5 sec.) 260˚C

ESD Rating (Note 4)

Human Body Model 2kV

Electrical Characteristics (Notes 2, 7)

Limits in standard typeface are for TJ= 25˚C, and limits in boldface type apply over the full operating junction temperature range (-40˚C to +125 ˚C). Unless otherwise noted, specifications apply to the LM2754 Typical Application Circuit (pg.1) with V

(IN, INSW)

= 3.6V, VEN= 1.8V, V

Symbol Parameter Conditions Min Typ Max Units

SETx

Dx/ISETx

Pin Voltage R

SETx

LED Current to Set Current Ratio (Note 11)

Current Sink Headroom Voltage (Note 10)

OUT

Output Voltage 1x Mode, IDx= 0mA 4.7 V

Output Impedance 1x Mode 0.25 Ω

Quiescent Supply Current 1x Mode, IDx= 0mA 0.7 mA

Shutdown Supply Current VEN= 0V 0.1 1 µA

Switching Frequency 0.7 1 1.3 MHz

Logic Input High Input Pins: EN, T/F, TX, SEL 1.2 V

Logic Input Low Input Pins: EN, T/F, TX, SEL 0.4

Logic Input High Current (Note 9)

Logic Input Low Current (Note 9)

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables.

Note 2: All voltages are with respect to the potential at the GND pin.

Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at T

120˚C (typ.).

Note 4: The Human-body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin.

Note 5: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be

derated. Maximum ambient temperature (T dissipation of the device in the application (P following equation: T

Note 6: Junction-to-ambient thermal resistance (θ standard JESD51-7. The test board is a 4 layer FR-4 board measuring 102mm x 76mm x 1.6mm. The 2 imbedded copper layers cover roughly the same area as the board. Thickness of copper layers are 70µm/35µm/35µm/70µm (2oz/1oz/1oz/2oz). Thermal vias are placed between the die attach pad in the 1st copper layer

A-MAX=TJ-MAX-OP

= 0V, VTX= 0V, V

T/F

SETx

IDx= 50mA to 100mA −7% 795 +7% mA/mA

= 200mA −11.5% 820 +11.5%

IDx= 200mA 550 mV

= 50mA 150

1.5x Mode, I

2x Mode, I

1.5x Mode 1.3

2x Mode 1.5

1.5x Mode, I

2x Mode, I

(EN, T/F, TX, SEL)

) is dependent on the maximum operation junction temperature (T

A-MAX

), and the junction-to ambient thermal resistance of the part/package in the application (θJA), as given by the

D-MAX

-(θJAxP

D-MAX

) is taken from a thermal modeling result, performed under the conditions and guidelines set forth in the JEDEC

= 0V, CIN=C1=C2= 2.2µF, C

SEL

= 4.7µF. (Note 8)

OUT

= 20kΩ −3.5% 1.244 +3.5% V

= 0mA 4.7

= 0mA 5.1

= 0mA 3.4

= 0mA 6.3 8

= 1.8V 4 µA

= 0V 0.5 µA

=150˚C (typ.) and disengages at TJ=

= 125oC), the maximum power

J-MAX-OP

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Electrical Characteristics (Notes 2, 7) (Continued)

and the 2nd copper layer. Ambient temperature in simulation is 22˚C, still air. Power dissipation is 1W.

LM2754

The value of θ conditions. In applications where high maximum power dissipation exists (high V For more information on these topics, please refer to Application Note 1187: Leadless Leadframe Package (LLP) and the Power Efficiency and Power

Dissipation section of this datasheet..

Note 7: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.

Note 8: C

Note 9: There is a 500kΩ resistor connected internally between each logic pin (EN, T/F, TX, SEL) and GND.

Note 10: Headroom Voltage (V

measured from V

Note 11: I

of the LM2754 in LLP-24 could fall in a range as wide as 35oC/W to 150oC/W (if not wider), depending on PWB material, layout, and environmental

IN,COUT,C1,C2

Dx/ISETx

: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics

) is the voltage across the current sinks (VDx) at which the current falls to 95% of the nominal programmed current. VHRis

to GND. If the headroom voltage requirement is not met, LED current regulation will be compromised.

Ratio was tested with the Charge Pump in a gain of 1x.

, high Gain, high I

), special care must be paid to thermal dissipation issues.

OUT

Block Diagram

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