BQ25504: Alternate circuit for testing solar cell

Hi Joe,

Thanks for the suggestion. I tried that but unfortunately I still get a 0V output. I checked the voltage across the cell and it is infact being held at the mppt point by the chip. 

I am not sure if it makes a difference in this case but I am getting 0V for VRDIV (pin 7) and consequently VBAT_OV (pin 6). I set it to 3.15V similar to 9.2.1 Solar circuit in the manual. However, I wasnt able to find much information about VRDIV in the manual.

Sincerely,

Kriti

Kriti,

VRDIV should be at the VBIAS voltage of about 1.25V. This only happens when VIN >= 0.5V and VSTOR >= 1.8V.

What is your input voltage?

Is VSTOR also sitting at 0V?

Joe

Hi Joe,

Yes, my VSTOR pin to which I have connected my 10k is also at 0V. When I connected the capacitors and removed the 10K resistor load I still got 0V for VSTOR.

My VIN_DC is from the solar cell which has 1V Voc made into 0.8V by the MPPT resistors.

Kriti,

I went ahead and modified an EVM I have to match your schematic. It worked fine with 0.8V at the input and a 10k resistor on VSTOR. Have you measured that the solar cell is outputting 0.8V?

If you can hook up a scope to your circuit I would be interested to see the waveform of VIN, VSTOR, and the switch node of the inductor.

I am also curious about the inductor you are using, what is the part number?

-Joe

Also, what are your resistor values for ROC1 and ROC2? (MPPT Resistors)

-Joe

Hi Joe,

I hooked up an oscilloscope to the pins. I get a DC voltage of 1.16 volts across the Vin pin and also at the inductor pin 16. The vstor and vrdiv are held at 0V. 

I am using the 22uH inductor purchased from mouser with part number 434-SMCCN-220K-02. Here is the link : http://www.mouser.com/ProductDetail/Fastron/SMCC-N-220K-02/?qs=sGAEpiMZZMsg%252by3WlYCkU45muCuneYXkTv5BU7HYFmY%3D

The Roc1 is 15.6Mohms made of (15+4.7+.1) and ROC2 is 4.4Mohms made of 2.2+2.2

I am thinking it maybe the chip which is broken so I am trying to acquire a new one that is already surface mounted. My current one is wire bonded with 100um wires.

Sincerely,

Kriti

Kriti,

With 1.16V Vin, the circuit should be working.

Wire bonding to the pads could definitely be the issue, you may have accidentally shorted pins together. Let me know how it goes with the part surface mounted.

Your inductor and resistors are fine. So, with a suface mounted part I am confident it will work as expected.

Regards,

Joe

Kriti,

Is there an update on this? I am going to close this thread, but you will still be able to post here.

-Joe