How to connect an LED?

[SHYAM THILLAINATHAN]

Hi, We are trying to connect a LED to one of the GPIO of nRF52840, we would like to know how to connect it. Connect it such that the nRF52 GPIO sink current or source current? Our LED Vf is 1V8 and current consumption is ~10mA. FUrther, nRF52840 is running at 1V8.

[Dave_couling]

In general its not recommended to run GPIOs and sources or sinks for LEDs. Better to run GPIO to the base of an NPN transistor to provide the ground path for an LED.

[SHYAM THILLAINATHAN]

Unfortunately, we don't have the luxury of adding a NPN due to size constraints. This is the part number for the LED we are planning to use: APHHS1005LSECK/J3-PF. Need to know if nRF52840 GPIO can handle it, if so, then in what mode: source or sink and in which drive configuration: standard drive or high drive. Will other GPIO get affected if I am driving a LED directly from a GPIO?

[Dave_couling]

Thats too bad, well as long as you have current limiting resistors inline (these LEDs are 2mA If), it doesn't really matter but I'd say source from the GPIO. Also note that using a GPIO to source/sink an LED can in cases introduce noise into your circuit.

[ovrebekk]

Hi

The amount of current the chip can sink/source depends in large part on the supply voltage, and with a supply of 1.8V we can't guarantee much more than 2-3mA from the pins, even in high drive mode.

If you think this is sufficient then you can connect the LED directly, just make sure to add the necessary resistance.
The GPIO should be configured in high drive mode.
It doesn't really matter if you choose sink or source. We sink the LED's on the devkits, but that is primarily to avoid the LED current affecting the chip supply current (for current measurement purposes).

Best regards
Torbjørn