LM3224

SNVS277C – DECEMBER 2004 – REVISED MARCH 2013

www.ti.com

The LM3224 can be configured to drive high current white LEDs for the flash and torch functions of a digital

camera, camera phone, or any other similar light source. The flash/torch can be set up with the circuit in

equation:

(23)

To flash the circuit pull the SHDN high for the time duration needed for the flash. To enable a lower current torch

mode a PWM signal can be applied to the SHDN pin. The torch current would then be approximately the percent

ON time of the PWM signal multiplied by the flash (or maximum) current. The optional disconnect FET can be

used to eliminate leakage current through the LEDs when the part is off and also to disconnect the LED when

the input voltage exceeds the forward voltage drop of the LED. The maximum output current the LM3224 can

supply in this configuration is shown in Table 1.

Figure 25 is another method of driving a high current white LED. This circuit has a higher component count but

allows the switcher to remain on continuously for torch mode reducing stress on the supply. The two FETs also

double for a disconnect function as described above. In this circuit the device and the torch enable FET are

turned on setting a lower current through the LED. When flash is needed the flash enable FET is turned on to

increase the current for the amount of time desired. The minimum ensured maximum output current for this

circuit is the same as for Figure 24.

Table 1. Maximum LED Drive current

LED Drive Current (mA)

4.2

1077

4.1

1047

4.0

1017

3.9

987

3.8

958

3.7

929

3.6

900

3.5

871

3.4

842

3.3

814

3.2

785

3.1

757

3.0

729

2.9

701

2.8

673

2.7

646

Table 2. Some Recommended Inductors (Others May Be Used)

Manufacturer

Inductor

Contact Information

Coilcraft

DO3316 and DT3316 series

www.coilcraft.com

800-3222645

TDK

SLF10145 series

www.component.tdk.com

847-803-6100

Pulse

P0751 and P0762 series

www.pulseeng.com

Sumida

CDRH8D28 and CDRH8D43 series

www.sumida.com

18

Submit Documentation Feedback

Copyright © 2004–2013, Texas Instruments Incorporated

Product Folder Links: LM3224