MP3331-2A SYNCHRONOUS BOOST FLASH LED DRIVER WITH I

MP3331 Rev. 1.02

www.MonolithicPower.com

12

5/3/2016

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OPERATION

The MP3331 is a single-channel flash LED driver

supports good image capture. It works in flash

mode, assist mode, torch mode, indicator mode,

and fixed 5V DC output mode.

LED Driver Operation

The MP3331 uses PWM mode with peak

current control to regulate the LED current. It

works

in

a

selectable

1M/2M/3M/4MHz

switching frequency with a synchronous rectifier

PMOS. When enabled, the synchronous PMOS

works as a 350mA current source to charge the

The device will change to boost switching mode

if the voltage across the current source is less

pass mode automatically to minimize the power

loss. In pass mode, the synchronous PMOS is

turned on completely. During the current start-

up, the current ramps up smoothly step by step

until the target setting current is reached.

Table 1: Mode Configuration

Configuration

TX/TOR

STR

LED_EN

STR_MOD

5V_MOD

LED_MOD

Mode

High

X

1

0

X

00

Torch

X

X

1

X

X

10

Assist light

X

X

1

X

X

01

Indicator

X

High

1

1

X

11

Flash

X

X

1

0

X

11

Flash

High

High

1

1

X

00

Torch to flash

X

High

1

1

X

10

Assist to flash

X

X

X

X

1

X

5V

Standby Mode

is ready to communicate with the host. Table 1

shows all work modes for MP3331.

Torch Mode

In standby mode, if TOR goes from low to high

(TX/TOR = 1), the device switches to torch

mode, and the current ramps up step by step

after setting LED_EN to 1. The current for LED

is set through register I_TOR. The ramping up

slew rate is set by register TUP_I. The current

is disabled by pulling TOR to low or by setting

LED_EN bits to 0. By pulling TOR to low,

LED_EN

and

LED_MOD

bits

will

reset

automatically to default if LED_SD is 0 (see

Figure 3).

Figure 3: Torch Mode

Assist Mode

To enter assist mode, set LED_MOD register to

10 and LED_EN to 1. The current ramps up to

the target value, which is set by I_TOR. The

ramping up slew rate is set by register TUP_I.

The current is disabled by switching to standby

mode or by setting LED_EN bits to 0 (see

Figure 4).