BQ25570: reference design

Hi Viktorija,

There is no reference design.  However, since this device only regulates the storage element with constant voltage (CV) and there is no charging current regulation, there is nothing special to do when using a supercap.  If the supercap does not require undervoltage protection (most do not), like most LiIon batteries without integrated protectors, you can short VBAT to VSTOR with the supercap connected at VBAT=VSTOR. Datasheet fig 32 shows typical charge waveform for this case.

If you want to avoid the long charge time in cold start until VSTOR=1.8V and do not need the integrated buck regulator, you can set VBAT_OV = 100mV +supercap voltage, place a 100uF capacitor at VBAT, short VBAT=VSTOR, place the super cap at the buck regulator output, VOUT and set the VOUT regulation to the supercap voltage.  Datasheet fig 33 shows typical charge waveform for this case.

You can use the design spreadsheet at the link below to size the resistors.

Regards,

Jeff