Battery optimization for nrf52832

[Ricky A. Rosa]

Hello,

I have a battery with 4.2v max charge. Since this is outside the input range for nrf52832, I have to add a down voltage regulator. Now the question is: Should I down regulate it to 3.3 or 1.8v?

I have to drive an RBG LED that requires more than 3.3v but I would also like to extend the battery life as much as possible. I found this solution to drive nrf at 1.8v and boost the voltage using PWM to drive the LED: 

https://devzone.nordicsemi.com/f/nordic-q-a/75124/is-this-robust-nrf52840-1-8v-low-power-mode-driving-rgb-led-from-3-3v

But I would like to avoid the extra components if possible. So my question is: would down regulating to 1.8v instead of 3.3v help to substantially increase battery life given that the DCDC on the nrf52832 is enabled?

I found this post that says it doesn't but the argument here is that the coin cell is already within range so there's no need for external down regulating. 

https://devzone.nordicsemi.com/f/nordic-q-a/25919/will-adding-a-1-8v-buck-converter-extend-the-battery-life-of-the-beacon 

In this case there is a need for down regulating since the battery we're using goes to up to 4.2v. The LED will be used scarcely. Should I boost the 1.8v with PWM or should I just go with 3.3v? Does the amount of battery life gain justify the added components?

Best,

Ricky

[Simonr]

Hi Ricky

This will heavily depend on what kind of voltage regulator you're using between the battery and nRF52832. A DCDC regulator here will benefit the most of a higher voltage (3.3V) while an LDO regulator will benefit of dropping as low as possible (1.8V). If the DCDC is enabled on the nRF52832, that would benefit of a high voltage as well, so to save components, you can use a low voltage and cut out the DCDC components for the nRF52832. We have the Online Power Profiler which you can use to get an estimate of what the current consumption will be at various voltages and with various optional components like the DCDC and external LF clock enabled and not.

What voltage exactly do you need to run the LED? I can't speak for your plans to boost 1.8V with a PWM, but generally, the increased battery life from the optional DCDC components and LF crystal are generally worth it as you will be able to decrease the current consumption quite a bit in total, but it of course depends on your use case and the rest of your circuit.

Best regards,

Simon

[Ricky A. Rosa]

I'm sorry there was a typo: The LED needs at least 3.3v. So, let me break down the question further:

1) I have to down regulate the battery with an external DCDC. Given that the internal DCDC is enabled, will down-regulating to 1.8v with the external DCDC extend the battery life significantly as opposed to down-regulating to 3.3v?

Best,

Ricky