GPIO configuration to drive led

[User1321]

Hi Nordic, 

I want to control an LED with the nrf GPIO, the LED Anode is connected to VDD, through a resistor, and the cathode is connected to the GPIO. Under this configuration, the LED should be ON when the GPIO is LOW but i cannot get the signal to be really low. It is always minimum 0.8V when it should be completely 0V. I know there is something on the configuration that I'm missing but i have tried all configurations. 

  nrf_gpio_cfg(LED,
  NRF_GPIO_PIN_DIR_OUTPUT,
  NRF_GPIO_PIN_INPUT_DISCONNECT,
  NRF_GPIO_PIN_PULLDOWN  ,
  GPIO_PIN_CNF_DRIVE_H0D1 , // (high drive low, disconnected high).
  NRF_GPIO_PIN_NOSENSE);
  
  nrf_gpio_pin_clear(LED);

Could you please give me a hint of what is the problem? I am using the nrf52840, s140 and sdk_15.3

Thanks you in advance! 

[ketiljo]

The problem is that the LED draws too much current so that the pin can't be pulled low enough. This is not a problem for the pin, unless you're using it for something else that requires it to be at 0 V.

[User1321]

Yes, i require it to be a 0V. I want to connect that GPIO to another LED so i can turn on both LEDs by pulling that GPIO low.

Also i have a TVS in the middle with the second LED.

If the anode from the LED is connected to VDD, will the LED current consumption still be a problem for the GPIO?

[ketiljo]

Then you need to use a transistor to drive the LED.