Power supply via both battery and regulator?

[Yaro]

Hello,

I've a battery based device that uses a buck/boost to efficiently use entire battery voltage range (4.2-3.0) . This component have a low quiescent current between 25-45uA and regulate output to 3v3 (there's devices than doesn't work in lower voltage modes).

When device is off, there is no sense to keep this regulator active even low Iq . Since nRF have a good sleep mode with very low sleep current would be a better choice to use his internal LDO+DC/DC to keep device powered .

Problem arise when battery gets close to 3v3 . Internal LDO is no longer suitable and from datasheet only VDDH or VDD must be connect at time.

I can use diodes to keep both power on VDDH , but when voltage is lower to somewhere like 3.4v I should disconnect internal LDO due dropoff. Don't know if it's suitable.

Can you advice me an approach that I can use to overcome this problem if there's a solution?

Actually is an evaluation about possibility to increase device efficiency.

[helsing]

Hi Yaroslav, thank you for your patience.

You cannot dynamically switch between VDDH and VDD during runtime on the nRF52. A power-on reset (where both voltage rails are at 0V) is required before switching modes. If the voltage on VDDH is too low to power your devices (including dropout to VDD), this rail cannot be used. I recommend adding an external LDO to the battery, along with a switch to toggle between the LDO and the buck-boost converter. This setup would allow you to bypass the buck-boost converter to save power and supply direct power to VDD when necessary.