VDDH in, but VDD out not required - inductor needed?

[Chris]

Dear All,

I'm pretty sure this has been asked many times but I don't know the right keywords to search for.

Alright, on our custom board we have a PMIC with regulated sys voltage (< 4.2V) and a LDO (programmable, 3.3V typ.)

Currently, we're using the PMIC's LDO but under certain conditions, the LDO is not powered on automatically, and because there's nothing powering the nRF52 it can't force-enable the LDO via I2C. If everything works fine (95% of the time) we see < 10uA idle current with Zephyr. That's awesome and I want to keep it in this range.

The idea is to use the PMIC's LDO only to power external ICs and use the Vsys for nRF52's VDDH, making sure "it always works"

Finally, here's the question: comparing Reference Circuit 2 vs Reference Circuit 4 the main difference is the lack of the inductor L4. Given the fact that we won't use VDD_nRF externally, do we still need the inductor for lowest power consumption (because DCDC stages are required internally in the chip and won't work without the inductor, right?)

[ketiljo]

REG0 DCDC will lower the current draw when you power the device from VDDH. The DCDC will be more efficient than using REG0 in LDO mode. So I'd recommend to use the DCDC also when it's only powering the nRF.

[Chris]

Thank you, ketilijo