max gpio current for nRF52

[Luis]

Hello, I just wanted to update previous similar questions for the nRF52 series, old one for nRF51 is here: devzone.nordicsemi.com/.../

At page 151, section 20.4, of the nRF52832 Product Specification v1.0 I find that GPIOs configured as high drive can source a maximum of 14mA and sink a maximum of 15mA, if VDD >= 2.7 V.

1. What is the limitation of the total current we can source/sink at the same time in multiple pins? For example in nRF51 you could have 3 pins sourcing 5mA at the same time, so maximum 15mA.

2. These max values are for steady constant currents rigth? Just wanted to confirm.

3. At the table we can find min, typ, max values. Do they mean that due to fabrication differences, some chips' pins will only be able to source 6mA instead of 14mA?

4. If number 3 is true, what happens if we try to source 14 mA from a pin that only supports 6mA? Will it break or will it limit this current to 6mA?

5. Looking at next page of the document, page 152, from graphs I get higher values for these currents, around 25mA. What is the difference or what am I missing?

Thank you very much, Luis Rodenas

Edit: minor changes to make it more clear

[IvanD]

Make a look on the LED: SML-LX0404SIUPGUSB It is a very bright one and maybe you could save current a little bit.

[Luis]

Thank you for the recommendation. That led does not seem bright enough, its datasheet says 20-40 mcd at 2mA, while mine (CLMVC-FKA) says 30-140 mcd minimum at 5mA. I will anyway explore this option of changing to a lower power LED and use nRF52 sinking instead of sourcing current.

[RK]

I drive all LEDs via MOSFETs so I don't need to worry about sourcing/sinking too much current from the nRF chips. Low voltage logic MOSFETs are available cheaply, in pairs if you like. You can have LEDs as bright as you like and and have as many of them on at the same time as pleases you.

[Luis]

I also usually use MOSFETs for leds, but I am studying the option to remove them. Things I don't like about having mosfets for my rgb led:

• Each mosfet needs 2 extra resistors, one to limit the gate current and one to make sure the mosfet will be off (for example) even if the gate pin is in undefined behaviour.
• If you dont limit the gate current with "big" resistor, instant charge currents can get quite high, and this gets important if you are switching the led at some high frequency or doing PWM on the gate to change luminosity.
• To use a RGB led means to use 3 mosfets + 6 resistors... so part counting goes up, also pricing and pcb area.

Of course it has its benefits, like being able to use higher current leds.

I may try to find smaller package with maybe 3 or several mosfets inside... I need my small rgb led to be visible at day ligth from a distance of a pair of meters... So not sure what option I will be following yet.