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BQ25505: BQ25505 battery charger

Part Number: BQ25505

I have the following circuit: 

The BYP and REF capacitors are ceramic and the remaining capacitors are electrolyte. I have made another circuit for the BQ25570 with these elements with no problem. Also, the BAT2 voltage is 3.7V, not 9V. 

The problem that I have here is that the boost charger does not seem to be working.

1- The VIN_DC is the same as the solar cell Voc. 

2- The VREF_SAMP voltage is zero. I tried other capacitors but made no difference. 

3- The Lboost voltage is the same as the VIN_DC. 

4- The VSTOR voltage is around 150mv lower than VIN_DC. 

5- The VIN_DC voltage does not change every 16 seconds meaning that the MPPT is not taking samples. 

6- Voltage on the C1 capacitor stays at VIN_DC and does not increase. I initially had the OK_HYST and OK_PROG pins connected to mid-point of external resistors but that did not make a difference.  

I was wondering if I could get some help on what might be wrong with this circuit. 

Thanks! 

  • Hello,

    Can you please try using Roc1 and Roc2 on you application circuit, to sample reference voltage stored on VREF_SAMP pin?
    Also, then your VREF_SAMP = VIN_DC(Open Circuit) * (Roc1/(Roc1+Roc2)).
    Thank you.

    Best Regards,

    Upal Patel

    Product Marketing Engineer

    Texas Instruments Inc

  • In reply to Upal Patel:

    Hi Upal,

    I connected the VOC_SAMP pin to the mid-point of two 10MOhm resistors (between VIN_DC and ground). But the VREF_SAMP voltage is still at zero. It seems that the MPPT modulate somehow does not work at all. All the voltage measurements are the same as what I reported in the question.  

    Vahid 

  • In reply to Vahid Montazeri63:

    Just wanted to let you know that I replaced the IC with another one and this time it works as expected. So I guess the first IC was damaged during the soldering process.

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