How to connect an LED?

RE: How to connect an LED?

ovrebekk — Fri, 15 Dec 2017 15:56:49 GMT

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

RE: How to connect an LED?

Dave_couling — Fri, 15 Dec 2017 00:01:43 GMT

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.

RE: How to connect an LED?

SHYAM THILLAINATHAN — Thu, 14 Dec 2017 23:09:45 GMT

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?

RE: How to connect an LED?

Dave_couling — Thu, 14 Dec 2017 21:08:43 GMT

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.