MP3331-2A SYNCHRONOUS BOOST FLASH LED DRIVER WITH I

MP3331 Rev. 1.02

www.MonolithicPower.com

13

5/3/2016

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Figure 4: Assist Mode

Indicator Mode

The device enters indicator mode, which

provides a low current output when LED_MOD

is set to 01, and LED_EN is set to 1. In this

mode, the driver current sources the output

current in 31.5kHz PWM mode. The current

amplitude is set by I_TOR while the duty cycle

is set by the INDI_PWM register. When

disabled, switch to standby mode or set

LED _EN bits to 0 (see Figure 5).

Figure 5: Indicator Mode

Flash Mode

The device works in flash mode in the following

ways:

1. Hardware and level sensitive mode.

In this mode, STR_MOD = 1, STR_LV = 1,

LED_EN = 1, and LED_MOD = 11. The flash

current starts ramping up after STR goes high.

The current is set by I_FL, and the ramping up

time is set by TUP_I. The flash current ends

when STR is pulled to low. If LED_SD = 0, the

LED_MOD is reset to standby mode, and

LED_EN is set to 0 after the flash. If

LED_SD = 1, the LED_MOD, and LED_EN are

not reset. If the flash timer set by FL_TIM ends

before STR goes low, the flash current

terminates immediately.

LED_MOD and LED_EN are reset to the default

value, and the time-out fault bit FT_TO is set to

1 and is not cleared until read back or input

power reset (see Figure 6).

Figure 6: Hardware and Level Sensitive Mode

2. Hardware and edge sensitive mode.

In this mode, STR_MOD = 1, STR_LV = 0,

LED_EN = 1, and LED_MOD = 11. The flash

current starts ramping up after STR goes high.

The current is set by I_FL, and the ramping up

time is set by TUP_I. The flash current ends

when the flash timer set by FL_TIM ends. If

LED_SD = 0, the LED_MOD is reset to standby

mode, and LED_EN is set to 0 after the flash. If

LED_SD = 1, the LED_MOD, and LED_EN are

not reset (see Figure 7).