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BQ51050B Charge Current

Jonas Sigmund
Prodigy 20 points
Other Parts Discussed in Thread: BQ51050B

Hello all together,

I try to fix a design that we have used for a prototype. Your setup is using a BQ51050B with a coil from Würth Elektronik, to charge a 350mAh lipo. It should be charged with a maximum rating of 350mA.

The R ILIM is set to 680 Ohms and the RFOD to 200 Ohms which should bring us a charging current around 357mAh (measured it’s around 899 Ohm so we should be under 350mAh) instead we getting the following current measured with an power analyzer:

I check the resonant capacitor and all other capacitors in the circuit.

They are set to the value from the typical application schematic in the datasheet. The prototype has been designed in January, because of this we didn’t know that the minimum charging current is 500mA as could be seen in the currently datasheet. Is this the reason for our problems or could it be done in this setting and there is another cause?

Best Regards,

Jonas Sigmund

  • 0
    TI__Expert 7730 points

    Do you use the same coil as what is on our EVM? Can you share your schematic?

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Prodigy 20 points

    Thanks for the quick response.

    We do not use the same coil, it’s the 760308101303 from Würth with an inductance of 47.0µH (Datasheet) and measured in our design with an inductance of 102.5µH (1V RMS; 100 kHz). The big difference of the inductance is caused by an additional Ferrite Shielding. The calculated resonant capacitors have a value of C1 = 24,712nF and C2 = 551pF.

    I will update our schematic tomorrow and attach the current version of it.

    Yours sincerely

    Jonas Sigmund