Configuration of GPIO for shared LED connection

[JPMorganJeremy]

Hello team,

Due to very constricted space on PCB, I am sharing one green LED between to IC's. 

U1 is the NRF52832, and U2 is a Lipo Battery Charger IC. I want either one of the IC's to

be capable of turning on the LED (providing ground connection).

The LED will turn on in a few cases:

1) The charger IC is provided with USB power, resulting in its power good pin pulling low, which turns on LED constantly (until power is removed).

2) A peripheral connects to the 52832, resulting in the software blinking the led for 2 seconds.

 -- In the case that that USB power is connected, and the LED is already on, I don't need it to blink when a connection is established.

My question is if there is a safe configuration of the NRF52832 GPIO, given the below circuit.

P1 on the Charger IC is an Open-drain output that goes low when USB power is supplied.

I just want to make sure neither IC is damaged during any pin states. 

[Dmitry]

Hi,

If nRF is powered directly from V1 - yes, it's safe (you can even save more space by using a single resistor at anode side - but don't forget to configure LED pin on nRF as an open-drain). If you have some power switch or LDO for nRF, you should take power for LED from an output of the switch/LDO.

[JPMorganJeremy]

Great, so I'm thinking this would be the config?

nrf_gpio_pin_dir_t 	    NRF_GPIO_PIN_DIR_OUTPUT
nrf_gpio_pin_input_t 	NRF_GPIO_PIN_INPUT_DISCONNECT 
nrf_gpio_pin_pull_t 	NRF_GPIO_PIN_PULLUP 
nrf_gpio_pin_drive_t 	NRF_GPIO_PIN_H0D1
nrf_gpio_pin_sense_t 	NRF_GPIO_PIN_NOSENSE 

And yes, thee entire board is powered by the 3.3V LDO of the U2 chip.

[Dmitry]

JPMorganJeremy said:

Great, so I'm thinking this would be the config?

PULLUP is not needed.

JPMorganJeremy said:

And yes, thee entire board is powered by the 3.3V LDO of the U2 chip

So, U1 is powered all the time (the anode of D1 is the same network as VDD of U1)? In this case your solution is ok.

[JPMorganJeremy]

Yes, same network. I actually decided to just trace the open-drain PG pin of the charger to a gpio on the 52832. I will just do a GPIOTE_CONFIG_IN_SENSE_TOGGLE. To see when it changes.