2.9V - 4.2V

LM3224

L

4.7 PH

2.2 nF

D

2k

22 PF

10 PF

ceramic

6.2:

(200 mA)

SHDN

3

6

SW

5

FSLCT

7

FB

2

GND

4

1

Battery or

Power Source

SS

8

High Current

White LED

Pull high for TORCH.

Pull Flash Enable high

for FLASH.

2.55:

(500 mA)

Torch

Enable

Flash

Enable

2.9V - 4.2V

LM3224

L

4.7 PH

2.2 nF

D

2k

22 PF

10 PF

ceramic

1.8:

(700 mA)

SHDN

3

6

SW

5

FSLCT

7

FB

2

GND

4

1

Battery or

Power Source

SS

8

High Current

White LED

Pull high for FLASH or

constant full current,

PWM for TORCH or

partial current.

Optional

Disconnect

FET

LM3224

www.ti.com

SNVS277C – DECEMBER 2004 – REVISED MARCH 2013

The 23V output is realized with a series of capacitor charge pumps. It consists of four stages: the first stage

includes C4, D4, and the LM3224 switch; the second stage uses C5, D5, and D1; the third stage includes C6,

D6, and the LM3224 switch; the final stage is C7 and D7. In the first stage, C4 charges to 8V when the LM3224

switch is closed, which causes D5 to conduct when the switch is open. In the second stage, the voltage across

C5 is VC4 + VD1 - VD5 = VC4

≊ 8V when the switch is open. However, because C5 is referenced to the 8V

output, the voltage at C5 is 16V when referenced to ground. In the third stage, the 16V at C5 appears across C6

when the switch is closed. When the switch opens, C6 is referenced to the 8V output minus a diode drop, which

raises the voltage at C6 with respect to ground to about 24V. Hence, in the fourth stage, C7 is charged to 24V

when the switch is open. From the first stage to the last, there are three diode drops that make the output voltage

closer to 24 - 3xVDIODE (about 22.8V if a 0.4V forward drop is assumed).

Figure 24. PWM White LED Flash/Torch Driver

Figure 25. Continuously Operating White LED Flash/Torch Driver

Copyright © 2004–2013, Texas Instruments Incorporated

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Product Folder Links: LM3224