Backlight driver pretty noisy on the power rail VSYS

[ranzbak]

Thanks to Renze :

This basically happens when the backlight is dimmed using PWM on the controller pin.

Several things can be done all with their own downsides :

• Add more capacity close to the display backlight controller
• Add a ferrite core before the capacitors, to reject the noise there
• Determine if the noise is problematic, if not leave it as is
• The datasheet describes an alternate method for diming, investigate that.

[ranzbak]

After using the scope to see if the difference in current drawn from the battery / USB power supply caused problematic rippling on the power rail voltage, we concluded, that the ripple (<70mV) is within the voltage ripple tolerance of the IC's used on the board.
So this is a no-fix.