LP5526

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SNVS431D – FEBRUARY 2006 – REVISED MARCH 2013

(mA)

4.3

28.3

4.7

25.9

5.1

23.9

5.6

21.8

6.2

19.7

Note that the LED output requires a minimum saturation voltage in order to act as a true constant current sink.

The saturation voltage minimum is typically 230mV defined with 10% current drop. If the LED output voltage

drops below 230mV, then the current will decrease significantly.

EXTERNAL PWM CONTROL

The GPIO[0]/PWM pin can be used to control the RGB output brightness or set RGB LEDs on/off. PWM function

for the pin is selected by writing EN_PWM_PIN high in GPIO control register (address 06H). Note, that EN_RGB

bit must be set high. Each LED output can be enabled with RSW, GSW and BSW bits. EN_EXT_R_PWM,

EN_EXT_G_PWM and EN_EXT_B_PWM bits are used to select, which LED outputs are controlled with the

external PWM input. Note that polarity of external PWM control is active high i.e. when pin is in high state, then

LED output is enabled. If RGB_PWM is set low, then each selected LED output is controlled directly with external

PWM input. If RGB_PWM is set high, then internal PWM control is modulated by the external PWM input. In

latter case, internal PWM control is passed to LED when external PWM input is high.

FLASH LED DRIVING USING RGB DRIVERS

RGB drivers can be connected in parallel and used as a flash LED driver (see Figure 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:

1. Using external PWM control

2. Controlling RGB max current register values

3. Using Flash mode

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 introduce pre-flash and flash.

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