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Debug BQ51050b circuit

user4169380
Prodigy 10 points
Other Parts Discussed in Thread: BQ51050B

Hi guys,

I am using this circuit (please see attachment) to charge a 700mAHr battery. I have the circuit wired up but does not work. Can someone please comment on the schematic and how I can debug and isolate the issue.

Thanks in advance

  • 0
    TI__Genius 14890 points

    Hello,

    I have reviewed the schematic and have a few suggestions.  

    1. TS_CTRL cannot be left floating.  It is used by the bq51050B as a temperature sense.  If that function is not required, then the pin must be tied to ground with a 10k-ohm resistor.  This effectively disables the temperature sense by indicating "25C" to the device.

    2.  You have a 700mAHr battery.  What is the planned charge current?  Use equation 1 to set the values of Rf and R36.

    3.  C1 on the AC1 pin is set to 183nF.  We recommend using multiple capacitors to achieve the desired capacitance.  Since all of the current entering the wireless system passes through this capacitor, any resistance in the capacitor turns to heat.  This can impact the value of the capacitor and will impact efficiency. C2 from AC1 to AC2 is typically 2 capacitors - mainly to get the precise value calculated.

    4.  I would suggest connecting the Pad (pin 21 in your schematic) to ground to allow for better thermal performance.

    5.  If this will be a Qi-compliant system, you will need to calibrate for FOD with Ros and Rf.

    For debug purposes, watch the RECT pin voltage.  That is the initial indicator of the AC1/2 power reaching the device.  When RECT reaches a high enough level, it will enable OUT.  However, as my first note above indicates, the TS_CTRL pin must be set properly before OUT will be enabled.

    Regards,

    Dick