NRF523840 Standard Drive, Output Current, and LEDs

RE: NRF523840 Standard Drive, Output Current, and LEDs

ketiljo — Fri, 19 Nov 2021 14:58:04 GMT

They're not in the datasheet. This is simulated.

RE: NRF523840 Standard Drive, Output Current, and LEDs

lorenzoFIL — Fri, 19 Nov 2021 14:06:14 GMT

This makes sense. Where can I find these graphs?

RE: NRF523840 Standard Drive, Output Current, and LEDs

ketiljo — Fri, 19 Nov 2021 14:00:59 GMT

The voltage drop vs. current curve in high drive looks like this:

Depending if you're sinking or sourcing.

Let's say you source 4 mA to a load connected between the pin and ground. The voltage drop will be 0.2 V, so the voltage on the pin will be VDD - 0.2 V,

You want to use high drive when you're driving a LED directly.

RE: NRF523840 Standard Drive, Output Current, and LEDs

lorenzoFIL — Fri, 19 Nov 2021 13:34:34 GMT

Thanks for the reply ketiljo.

So the 0.5mA for standard drive implies that I can reliably have Vdd when I'm trying to source 0.5mA. However if I were to pull more current, I can expect to see the 1mA-4mA however down to Vdd - 0.4V?

I think it's becoming more clear to me now. The source of the "internal resistance" is from the (I assume) FETs in the microcontroller which gate the output voltage. Right?

RE: NRF523840 Standard Drive, Output Current, and LEDs

ketiljo — Thu, 18 Nov 2021 14:07:00 GMT

The GPIO will limit the current due to the internal resistance in the GPIO output driver. The current that's stated as max current for standard and high drive it when you need to have a guaranteed voltage on the output. If you draw more current the voltage will be lower or higher depending if the output is high or low.

It's like having a second, internal, resistor in series with the LED of about 50 ohm in standard drive and 20 ohm in high drive.