LP5526 datasheet(15/33 Pages) NSC

15 / 33 page

Functionality of Color LED

Outputs (RLED, GLED, BLED)

(Continued)

FLASH LED DRIVING USING RGB DRIVERS

RGB drivers can be connected in parallel and used as a

flash LED driver (see Typical application 2). Flash LEDs can

be powered through the boost converter. Flash LEDs are

controlled basically the same way as RGB LEDs controlling

is previously described. Additional safety mode is introduced

for FLASH LED driving to avoid prolonged flash and damage

to application. FLASH can be done in 3 different ways:

Using external PWM control

Controlling RGB max current register values

Using Flash mode

1. Using External PWM control

In this case pre-flash brightness is adjusted by adjusting the

pulse width of PWM signal

•

Enable external PWM pin by writing EN_PWM_PIN bit

high

•

Use EN_EXT_R_PWM, EN_EXT_G_PWM and EN-

_EXT_B_PWM bits to select, which LED outputs are

controlled by the external PWM control. Output which

external PWM control is not selected will be on constantly

regardless of the state of the external PWM pin.

•

Enable RGB constant current mode, if external ballast

resistors are not used (CC_SW = 0)

•

Disable internal RGB PWM mode (RGB_PWM = 0)

•

Write wanted maximum current values for each output to

RGB max current register (e.g. 11b for maximum current)

•

Enable RGB functions (EN_RGB = 1, RSW= 1, GSW= 1,

BSW=1)

•

Use external PWM control pin (GPIO[0]/PWM) to intro-

duce pre-flash and flash.

20179702

Using External PWM Control for Flash

2. Controlling RGB Max Current Register Values

In this case pre-flash brightness is adjusted by adjusting the

current values in the RGB max current register. Note that in

this mode flash control speed and timing depends on the I

communication speed.

•

Enable RGB functions and disable PWM mode (EN-

_RGB = 1, RGB_PWM = 0)

•

Enable RGB constant current mode (CC_SW = 0)

•

Write pre-flash values for each output to RGB max cur-

rent register (e.g. 00b for 25% of maximum current)

•

Start pre-flash by switching on the LEDs (RSW = 1, GSW

= 1, BSW = 1). Pre-flash brightness can be adjusted also

by setting on only one or two LEDs during the pre-flash

•

Start flash by writing each output maximum current val-

ues to RGB max current register

•

Stop flash by switching off the LEDs (RSW = 0, GSW = 0,

BSW=0)

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