So I’ve been working on a project where power consumption is a major concern as the tags need to be powered by batteries and they should last as long as possible. The target power consumption is ideally in the tens of µA up to a max of a couple hundreds of µA on average (of course during radio activity it would be much more)
Right now we’re designing the pcb to integrate a DMW1001 module with our other sensors and components but we couldn’t really find any document advising us on what to do with the pins we don’t use. I know some modules consume more on idle wasting energy if some specific pins are left floating or pulled up/down when the opposite should be done, so any help on that would be much appreciated.
Also, any other general tips on designing pcbs for low power applications would be very much welcome.
What kind of RF ping rate (ranging update rate) are you looking for? Are you planning to use motion sensing to help assist with power management?
Another consideration when using small batteries is that the instantaneous current demand can be too high for the battery and it will usually hit some kind of over current protection or be damaged. We have devised some ways around this using an intermediate energy store, however, this needs a custom design of the tag instead of the DWM1001 module. If you would like more details on this please do let me know.
In terms of the DWM1001, unused pins can be left floating without inuring additional power consumption.
We tried to use CR2450 and TPS61097A-33, but the results depend on the firmware. I think it can work fine with TDOA approach, where radio time is very short. Using TWR didn’t look feasible for us, as the currrent peak took too long for such a battery.
The consumption of DCDC converted (buck or boost) can be very long (a few uA). Much more important in the battery and maximum current it can source. Of course, with higher voltage, less current is needed, but we wanted to use coin cell type.
Hi @rastik thanks for the details i will try out this circuit. I am also trying too use a coin cell only. With CR2450 what kind of battery backup are you getting for TDoA? And I am planning to put a 470uF capacitor to prevent sudden current draw from coin cell. Would that work?
It depends on your firmware, you’ll need to test/calculate it. It depends on the transmit time and that depends on many parameters (payload length, tx speed, preamble length etc.). If you use large capacitors, be careful about leakage current, it can get pretty high.