npm1300 on-off switch question

[ecp]

Hello, 

I was wondering if there was a way to implement a physical on/off switch to the npm1300 that would allow the outputs to be isolated form the battery but still having the ability to charge the battery. 

I have attempted adding a switch between VSYS and PVDD as highlighted in the following image, but when the switch is in the off position, disconnecting VSYS from PVDD, the battery starts draining around 1 to 2mA. This is a higher drain from the battery than what it's using on the on position.  

Do you have any recommendations on where to add a switch to function as an on/off? I would prefer to use a switch than a pushbutton for my use case. 

Thanks. 

[runsiv]

That is expected, disconnected PVDD when the BUCKs are not explicitly turned OFF is not possible.

As for how to achieve this, I don't quite see an obvious way besides using a double-pole switch (DPST) and disconnecting the outputs of the BUCK from what they supply and let them idle in HYST mode.

Regards

Runar

[ecp]

What are the ways I could explicitly turn off the buck converters? 

[ecp]

Does this mean that if I add a switch that shorts VSET1 and VSET2 pins to ground like in the image below, it can act as an on/off switch for the system? 

Thanks, 

-Eduardo

[Tomi Koskela]

VSET1/VSET2 are monitored only on startup. So you cannot disable/enable the bucks with this connection "on the fly". You would need to configure the bucks to be controlled with GPIO (needs TWI writes to accomplish this) and then you could control the bucks with a switch. 

[ecp]

When I do this, configuring the bucks on/off through a GPIO, it gets into an invalid state upon turning off the buck that feeds the VDDIO. What should the VDDIO be connected to in order for this not to happen? The datasheet only recommends powering VDDIO with one of the bucks. 

[Tomi Koskela]

In typical application buck converter is used to supply VDDIO, the same rail that would power the SoC. This same rail would be the reference voltage for SoC TWI. One suggestion is using the same supply as you have for the device that controls the GPIO in this state. 

[ecp]

If the circuit is wired as in this example, how can you turn off the SoC by turning off the BUCK that powers it if VDDIO needs to be powered by that same BUCK?

Or stated differently: how would you turn the system off in this application example? (while still being able to charge the battery while off through USB). And how would you then turn it back on?

[Tomi Koskela]

In the example schematic you would use ship mode to turn off the system (entered with TWI write) and SHPHLD pin for waking up. VDDIO needs to be powered for TWI operation. If VDDIO is not present you would not be able to communicate with the device. Note the GPIO is also referenced to VDDIO.

[ecp]

Can the battery be charged through USB while in ship mode? I read in the datasheet that connecting the USB wakes up the npm1300 from ship mode.
Also, is it possible to set up a pushbutton to enter ship mode? 

[Tomi Koskela]

In ship mode the battery is effectively isolated from the system and it cannot be charged. Yes connecting USB will wake up the nPM1300 from ship mode. Unfortunately it is not possible to enter ship mode with push button, only with TWI write. 

[ecp]

but a pushbutton connected to the SHPHLD pin could be configured through software of the NPM1300 to generate an interrupt through one of its GPIOs when pressed. This GPIO would connect to a GPIO on the SoC, which could be configured to tell the NPM1300 through I2C to go into ship mode when this interrupt is received for a decided amount of time (5 second button press for example).
Is this correct?