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BQ25504: Some problems with output

Le Giang
Prodigy 180 points
Part Number: BQ25504
Other Parts Discussed in Thread: BQ25570,

Hi everyone,
I have some problems with my new battery charger board. I used a solar panel with Voc=4V and Isc=1mA to supply the board. The board is set with VBAT_OV=4.2V and VBAT_UV=3.0V.
The problem is when i measured the Vin voltage of the board, the meter showed only 1.8V. Next i measured VSTOR and VBAT pin they were only 1.3V.

Here is the schematic:

  • 0
    TI__Mastermind 21590 points
    Hi,
    If VSTOR is below 1.77V, the IC is still in Cold Start mode. Since VBAT < VBAT_UV, there will be no output since the FET between VBAT and VSTOR will be off.
    Regards,
    Raheem
  • 0 in reply to Raheem
    Prodigy 180 points

    hi Raheem

    What do you mean when saying VBAT>VBAT_UV

    . The VBAT is the battery voltage or the VBAT pin?  When I test the board i did not connect any battery to the VBAT pin. So you mean that i have to connect a storage hwhich has higher voltage than the VBAT_UV so the board will work? Adi i get it or not?

    Please reply as soon as possible

    Thank you!

  • 0 in reply to Raheem
    Prodigy 180 points
    I had connected a supercapacitor to VBAT pin and measured the VBAT was regulated at 5.4V. But the VBAT_OV i programmed was 4.2V. What wrong with my circuit?
  • 0 in reply to Le Giang
    TI__Mastermind 21590 points

    Hi,
    Can you please post scope shots of VIN, VBAT and VSTOR when this happens.
    Regards,
    Raheem

  • 0 in reply to Raheem
    Prodigy 180 points

    Hi,
    I had assembled a second circuit to test but i got no output in VBAT even when i connect a supercapacitor with 3.7V charged to VBAT pin. VSTOR was only around 600 to 700 mV. I have one concern that is when I connect the solar panel to VIN_DC and measure voltage on this pin, does it equal to the Voc of solar panel or decrease at a lower level? 
    Can you post some real parameter with board which similar to my configuration that already run for me please.
    Thanks and best regards,
    Giang

  • 0 in reply to Le Giang
    TI__Mastermind 21590 points
    Le,
    If VSTOR is around 700mV, the device is still in cold-start. The device exits cold start when VSTOR > 1.7V. The Voc of the solar panel will have to be measured when the solar panel is disconnected from the IC.
    Regards,
    Raheem
  • 0 in reply to Raheem
    Prodigy 180 points

    Hi,

    So could you please suggest something for me to help the IC exiting cold-start. Should I connect an external storage element like supercap to VSTOR? And normally how long does it take to exit cold-start(when VSTOR reaches VBAT_OV) when there is no system load?

    Regards,

  • 0 in reply to Raheem
    Prodigy 180 points

    Hi,

    I had done some new test and figured out that if I expose the solar panel directly to the sunlight, which Voc=4.5 and Isc=5mA, the charger boost up to 8.9V on bot STOR and BAT pin immediately. The same happens with 3V3 source from a launchpad kit. But with Voc=3.5 and Isc=0.072mA, the Vstor always around 1.4V, hardly up to 1.7V and never reach me OV voltage.

    Regards,
    Le

  • 0 in reply to Le Giang
    TI__Mastermind 21590 points
    Le,
    The recommended maximum input voltage is 3V . The voltage on VSTOR is more than is more than the absolute max of 5.5V. Try using a buck converter before the input.
    Regards,
    Raheem
  • 0 in reply to Raheem
    Prodigy 180 points

    Hi Raheem,
    1. After doing some tests, I have got some results:
    When I placed the solar panel in the room in which Voc=3.6V and Isc=0.07mA, I got VBAT = 1.67V and VSTOR=1.9V
    When I placed it outside in which Voc=4.5V and Isc=1.5mA, I got VBAT=7.3V
    I think the current plays an important part in the boost converter's operation. Could you suggest any idea to improve this situation?

    2. I selected an inductor different from those which recommended by datasheet but still had the same inductane value 22uH. Are other parameters such as current rating, saturation current or also important or only the indactance? The inductor i choosed is MLZ2012N220LT000 which has 300mA current rating and 70mA saturation current.

    Here are some scopes of VBAT


  • 0 in reply to Le Giang
    TI__Mastermind 21590 points

    Hi,

    Based on the VBAT_OV setting being equal to 4.2V, i don't expect the battery voltage to be above that so i'm surprised that VBAT is equal to 7.3V. Regarding the inductor selection, you'll have to follow the rule stated below.

     

    Regards,

    Raheem

  • 0 in reply to Raheem
    Prodigy 180 points
    Hi Raheem,
    Thank you for your reply. By the way, with my other project, I'm planning to harvest RF energy by an rectenna and use it to charge a battery or supercapacitor. Could you suggest some ICs or board regarding to that field?

    Regards,
    Le
  • 0 in reply to Le Giang
    TI__Mastermind 21590 points
    Le,
    The Bq25504 and BQ25570 should work depending on your application. The BQ25570 is similar to the BQ25504 except it has an integrated Buck at the output.
    Regards,
    Raheem