nRF52 Solar Reference Design

RE: nRF52 Solar Reference Design

K. Townsend — Fri, 26 Aug 2016 09:18:11 GMT

Thanks for the design notes. It might be useful to add to the infocenter guide for people who don't stumble across this post, but thanks for posting some more info here at least.

RE: nRF52 Solar Reference Design

TORS — Fri, 26 Aug 2016 09:08:39 GMT

The U5 switch is the actual switch that turn ON/OFF the radio. This switch is controlled by the Vgs treshold voltage in U4. The Vgs voltage level is again controlled by voltage devider R11, R12 and R13. R11 could in theory be merged with R12, but are implemented to create the hysteresis characteristics of the switch. The U4 turns on when the voltage level at pin 2 in U4 is higher than 1.4 V, as documented in its datasheet. To reduce the power consumption of the hysteresis switch, resistor values is made as high as possible. Because of small leakages, non-linear and parasitic effects in U4 and U5, the thoery doesen't correlate perfectly with practice. The theory should anyhow give you some ballpark values, while the last tuning has to be done manually. Unfortunately, I don't have any spreadsheets with optimal resistor values that represents the different voltage levels.

RE: nRF52 Solar Reference Design

K. Townsend — Thu, 25 Aug 2016 18:32:46 GMT

To further clarify, there is some minimal info on the hardware design here: infocenter.nordicsemi.com/index.jsp

Unfortunately, there are no notes on adjusting the resistor divider values, or any design notes on the specific values chosen, which is unfortunate since this is a particularly inexpensive solution to an interesting problem. A simple spreadsheet in the downloadable hardware folder would help a lot of people out taking a nice design and making some minor changes to it ... or even a quick one or two paragraph explanation of the decisions behind the design with the values and output clearly stated.

The dual FET ICs and resistor dividers I'm talking about can be seen here:

RE: nRF52 Solar Reference Design

K. Townsend — Thu, 25 Aug 2016 18:26:16 GMT

Yes, that's the board I'm talking about. I should have added the link for the sake of other viewers sorry.

RE: nRF52 Solar Reference Design

awneil — Thu, 25 Aug 2016 18:19:35 GMT

You mean this: infocenter.nordicsemi.com/index.jsp ?