Other Parts Discussed in Thread: BQ25570EVM-206
We are using BQ25505 boost charger to recharge a secondary battery.
Test setup description as below:
A discharged battery of 2.75V is connected across VBAT_SEC pin..
VIN_DC is supplied from a bench top power supply unit with 3.3V and 0.5A.
VSTOR output is directly connected to the VOC_SAMP pin on the board.
VREF_SAMP is connected to a low leakage 10nF capacitor.
With proper biasing setup through resistor drivers, we still don't see a charging current to the battery. With this context we observe the following:
1. VREF_SAMP is 16sec periodic signal with approx. 300msec pulse width and amplitude is around 2.10V.
2. VOC_SAMP & VBAT_SEC signal waveforms are similar - both are a pulsating train with 16sec repeatability and peak is 4.20V and it drops to 3.20V within 300msec.
3. We don't have the BQ25505 EVM. However when replicating the setup with BQ25570EVM-206, battery charging peak current is 40mA.
Could you please help us in understanding this behavior of BQ25505 device - why battery is not getting charged?
Is VREF_SAMP signal require to be static, not pulsating? Currently, a 10nF cap is connected, do you see it to be increased?