Dear All,
I am using BQ25504 to harvest energy from the high impedance source, whose open-circuit voltage is 17 V. The max current of the source is 20 uA at 400 mV.
I have designed the harvester circuit using BQ25504, as mentioned in the attachment. I expected that energy was harvested from the source and stored in the supercapacitor (5mF) connected to the VBAT pin. VBAT_OV is configured to 5.1V, and VBAT_UV is configured to 3.1 V. Once the supercapacitor voltage is reached 5.1 V, I should get a signal high at VBAT_OK pin and low when it reaches 3.1 V. Based on this signal, I can use external FET to connect the VSTOR pin to the load.
My testing observations:
When I connect my source to the energy harvester, voltage dips to 372 mV, and supercapacitor (VBAT) voltage and VSTOR voltage is increased to 1.2 V, and it settles there. Further increment in voltage is not happened even waited for more than an hour.
Later, using the function generator, I applied 400mV DC to the energy harvester circuit. The supercapacitor's voltage is increasing, and it reaches 5.1 V. At this point, I didn't get the VBAT_OK signal.
My doubts are
i) whether this energy harvester will not harvest energy from my sources.
ii) why I didn't get the VBAT_OK signal.
Please let me know that where I made a mistake in designing the circuits. Or suggest me suitable harvesting method as per my sensor.
Thank you,
Prakash S
