I've build a BQ25504 based circuit powered by a solar cell providing 2.2V (OC) and 110uA (SC). My circuit is an exact copy of the solar application circuit from the data sheet, adapted for my own requirements:
- Vbias = 1.25V
- Vbat_uv = Vbias (1 + Ruv2/Ruv1) = 2.7V
- Vbat_ov = 3/2 Vbias (1 + Rov2/Rov1) = 3.75V
- Vbat_ok_prog = Vbias (1 + Rok2/Rok1) = 3.0V
- Vbat_ok_hist = Vbias (1 + (Rok2 + Rok3)/Rok1) = 3.6V
- Energy storage is accomplished via a 1F 5.5V (ESR = 30 Ohm) supercapacitor connected to VBAT
My wireless circuit (the load) takes power from the VSTOR pin.
Depending on the level of solar energy, VSTOR varies from 0.65 V to >4V but no energy seems to be retained by the supercapacitor. Even after one hour under direct sunlight (VSTOR > 4V), moving the circuit to a shadowed place makes the voltage rapidly drop to 0.65V. Moreover, I expected the BQ25504 regulator to never let the output voltage go over Vbat_ov but this is not the case.
I know this is a tuning-related problem and I admit not having studied the specifications in detail. I initially hoped that using the BQ25504 IC would be more straightforward but I was obviously wrong.
Any suggestion is welcome!
Thanks in advance.
Daniel.
