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How bad it is to power LCD backlight from MCU IO?

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3dgeo:
Hi,

I want to cut some components from BOM, so I thought could I just power 80x160 px LCDs backlight directly from STM32F411 IO pin, how bad of the ide it is?
I want to have a way to turn LCD off.

Ussualy this LCD is powered like this:


But according to LCD datasheet backlight takes 15mA:


And STM32F411 IO is capable sunking/sourcing up to 25mA:


So here I'm...

There will be no other high power demand from MCU IO, logic only.

madires:
Should work fine. One disadvantage could be the impact of the PWMed current on sensitive MCU functions like the ADC.

3dgeo:

--- Quote from: madires on March 12, 2020, 03:14:42 pm ---Should work fine. One disadvantage could be the impact of the PWMed current on sensitive MCU functions like the ADC.

--- End quote ---

By "PWMed current" you mean backlight PWM? Would be nice feature to use PWM on BL to dim the screen...
Anyway, not using any analog stuff, only digital IO (regular digital IO, I2C, SPI).

madires:
Yes, I meant backlight PWM. And don't skimp on bypass caps. ;)

SiliconWizard:
Just a thought - given the typical Vf of 3V (what about dispersion?), this is close to a 3.3V rail. There's bound to be some dispersion in backlight brightness from one unit to the next unless you can sort of adjust it. It may not matter if you're building just one unit or if you don't care about that as long as it's just lit up.

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