PCA9955B LEDx output signal strange behaviour

[RL18]

Hi,

I am trying to change individual LED brightness control with Registers PWM0 to PWM15.

LED driver output state are set for all LEDs to LDRx = 10 — LED driver x individual brightness can be controlled through its PWMx register (default power-up state) or PWMALL register for all LEDn outputs.

The output current value for all LED outputs are set with Register IREFALL

The brightness of all LEDs can be changed, but LED0 isn't as bright as LED1-15

LED0 seems to supply a PWM signal, whereas LED1-15 seem to regulate the current via PWM.

Is there any exception for LED0?

LED0

LED1-15

Schematic

[TomasVaverka]

Hi Robert,

I requested the IC architect to double-check the implementation, but as far as I know all channels are identical.

The maximum current skew between channels should be less than 4 % as described in the datasheet, chapter 7.3.14 and table 33.

I will update this thread as soon as I have the feedback from the IC architect.

Best regards,

Tomas