Npm1100 SHPHLD button shared with GPIO

RE: Npm1100 SHPHLD button shared with GPIO

Bram de Wit — Mon, 28 Jul 2025 15:42:51 GMT

Hi,

I know this is an old thread, but I have the same design constraints, so I figured this answer might also be useful to others

If you want to have the SHPHLD pin attached to a button that is also attached to the I/O of an MCU you could simply configure the button as active low and use a diode to prevent current from flowing from the SHPHLD pin towards the MCU.

Here you can see how that would look like with the button pressed. The MCU voltage is still pulled to a logic low level.

And here you can see what that would look like with the button unpressed/floating. As you can see there is no current flow

Kind regards,

Bram

RE: Npm1100 SHPHLD button shared with GPIO

Jared — Mon, 31 Jul 2023 14:24:31 GMT

[quote user="mccleanp"]The device is a small wearable device - there simply isn't space for many buttons. I was intending to use the ship mode as the main power-off mode since it isolates the battery, instead of powering down the MCU and all the peripherals. Maybe this is the wrong approach?[/quote]

Just to be clear, you can still put the device into ship mode and exit it without using SHPHLD:

There are two ways to exit Ship mode. Either connect the USB (VBUS) or set SHPHLD low for a minimum period of t_shipToActive. The battery supply (VBAT) is used to hold SHPHLD high through a weak pull-up resistor when Ship mode is enabled. A circuit to pull down SHPHLD is optional (see the Button switch shown in the following figure). If no pull-down circuit is present, Ship mode is exited when VBUS is connected.

If you're restricted to only using one button then I think you have the choice of either not using the pull-down circuit and only rely on VBUS, or using a level shifter as you've shared.

regards

Jared

RE: Npm1100 SHPHLD button shared with GPIO

mccleanp — Mon, 31 Jul 2023 12:09:25 GMT

Thanks for your reply Jared.

The device is a small wearable device - there simply isn't space for many buttons. I was intending to use the ship mode as the main power-off mode since it isolates the battery, instead of powering down the MCU and all the peripherals. Maybe this is the wrong approach?

So the idea was that one of the application buttons could be used to power it on by pulling SHPHLD low. I was thinking of implementing the level shifter like this:

This should work fine, but results in a small current drain of approx 230uA when the button is not pressed. I suppose I could use a GPIO output instead of 3V0 VDD and only turn it on when scanning the button. but even this could become significant over time.

RE: Npm1100 SHPHLD button shared with GPIO

Jared — Mon, 31 Jul 2023 11:33:42 GMT

Hi,

What is your motivation to use the same button for a GPIO that you already use for SHPHLD, note that you're not forced to pull SHPHLD low to exit ship mode, you can also just plug in VBUS. That will make it exit ship mode.

[quote user=""]

If the button is connected to both SHPHLD and a GPIO pin I am concerned this will connect VBAT to the MCU and will slowly drain the battery. Also VBAT is 3.7 where as VDD is only 3.0.

[/quote]

Exposing the nRF52832 to 3V7 when VDD is 3V0 violates the absolute maximum ratings and can result in damaging the chip.

How are you thinking of implementing the level shifter?

If you absolutely don't want to add a second button then I would go with the level shifter if you're able to make it work with that,

regards

Jared