Hello, Please help:
I am trying to design a solar application based on the BQ25504. The system is supposed to charged a rechargeable 3.8 V Li-ion battery while using a cell with maximum 4v output. the energy from the battery will be used to power up a MCU when it is needed. I have arranged my resistors network around the BQ25504 chip as following:
VBAT_OV : ROV2 = 5.4M ROV1=4.4M
VBAT_UV: RUV2 = 4.8M RUV1 = 5.2M
VBAT_OK_HYST: ROK3: 680K ROK2 = 5.1M ROK1=4.2M
VOC_SAMP : ROC2 = 3.6M ROC1 = 16.4M
all capacitors and Inductor and the rest of the components have been chosen based on the datasheet recommendations.
>> problem 1: when I connect a fully charged battery (3.7 v) to the VBAT pin, I am expecting the VSTOR to be shorted to he VBAT inside the chip through a PFET. but this is not happening.
the only way to make the PFET to switch on is to apply a voltage to the VIN_DC > 450 mV (increasing the voltage on the VIN_DC gradually increases the VSTOR gradually to the point it reaches VBAT_UV) to make it happen. and after ward if I remove the power from the VIN_DC the switch remains on and VSATOR remains shorted to VBAT to feed the load.
I know that the only time the PFET switch is on is when VSTOR > VBAT_UV.
my question is that: why the connection between the VBAT and the VSTOR doesn't happen automatically. I believe, this should take place according to datasheet and all the researches that I have done.
where am I wrong?
thank you very much for any help.
