Hi, we are building a design off of the impc001 breakout dev kit. No matter what the power source is, it looks like the BQ25895 chip transforms the power. Is the VMOD output should be 5.0VDC?
We measured our VMOD test point at 4.6VDC. VMOD then powers the RGB LED and the MP2141NGTF buck to get 3V3 for the rest of the system. Since we do not need the BQ25895, we are removing it and want to make sure we output the correct voltage for VMOD.
According to our datasheet, VMOD is min 3.3V, nominal 3.9V, max 4.5V. Note that in the European model, the VMOD current can, for brief periods, get quite large (2.4A) and it still oughtn’t droop below 3.3V.
As Peter says, VMOD should be max 4.5v; with the PMU initialized, you should be seeing 4.2v at VMOD (without it initialized, because some boards incorrectly had the BQ25895M vs BQ25895, you’ll see ~4.3v there).
In most customer designs not using the BQ part (ie they have no need for battery management), they pick ~3.9v for VMOD.
I would like to revisit my old post here. I’m measuring VMOD on the ImpC001 DevKit as ~4.5vdc, which is at the max limit for the chip. I think the reason VMOD is set to the max is because it also powers VMOD_GATED which powers the RGB LED D1 SSK9822. This LED is 5v which min is rated for 4.5v.
Early impC001 breakouts had the wrong BQ25895 revision with the float voltage a little high.
Vmod will, without running any code, be at appx 4.35v. If you bring up the BQ PMU class, defaults will reset this to 4.2v: https://developer.electricimp.com/libraries/hardware/bq25895
LED is ok with ~4v generally.
I agree with @hugo. We were able to get the LED running off of VMOD_GATED running near ~4.0vdc.