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BQ25504 Energy Harvetser Issues

Priyesh P P
Prodigy 130 points
Other Parts Discussed in Thread: BQ25504

Hi,

I am using BQ25504 for harvesting energy from a 3V (Voc) 150mA (Isc) Solar panel to charge a 3.7V, 680mAh Li-Po battery. I made a prototype PCB based on the application circuit given in the data sheet with the following design conditions,

VBAT_OV = 4.2V          VBAT_UV = 3.0V

VBAT_OK = 3.3V          VBAT_OK_HYST = 3.7V

VIN_DC = 3.0V             VREF_SAMP = 2.34V

I used (SLURAQ1 excel calculator for selecting resistors. 

For the purpose of testing, I connected a Li-Po battery (charged, around 3.72V) to the VABT pin and set VINDC = 1V using a DC supply. The circuit draws 20mA from the DC source. I kept this running for around 4 hours. When I checked after that,  VSTOR is  found to be 0.951V and VBAT_OK is 0V. I tried increasing VINDC and saw that at VINDC = 2.117V ,VSTOR = 1.8V and current drawn by the circuit is 6mA and at VINDC=2.38V(~VREF_SAMP)  VSTOR is connected to VBAT and I get  3.72V at this pin and 3.7V at VBAT_OK pin. Now, the circuit draws current only in uA from the DC supply and it is not charging the battery even if I decrease VINDC below 2.38V. In short, I couldn't get the device  working as expected.

Is there anything I am doing wrong?Can any one give me a hand with this?

Thanks

Priyesh

  • 0
    TI__Guru**** 165886 points
    The IC is expecting a high impedance source not a low impedance power supply. Add a resistor in series between power supply and VIN_DC, sized R= (VPS-VOC*0.8)/150mA, or current limit your power supply to 150mA. Current limiting some power supplies does not work as well as using a resistor.
  • 0 in reply to Jeff F
    Prodigy 130 points

    Hi Jeff,

    I tried current limiting the power supply, but it doesn't  work. I tried connecting it to the solar panel . I kept the solar panel around 3 hours in a place where strong sunlight is available. Still, no good results. VBAT_OK never goes high(3.7V) and VSTOR remains at 1.3v when connected to solar panel.

    Thanks for your suggestions.