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BQ24650: low charging current

Michele Pedroni
Prodigy 110 points
Part Number: BQ24650

Dear Sirs,

we have designed a battery charger for a 12V LiFePo4 battery using the BQ24650.

The circuit does not work as expected, on the output the DC voltage presents regular voltage dips and the maximum charging current is 250mA.

Even without load connected, we can notice the aforementioned drops in the output.

I attach the circuit and 3 graphs from oscilloscope showing the voltage output with a load of 250mA, 100mA and no load.

 The circuit was designed following the schematic of the EVM.

Do you have any idea of what could be wrong with the circuit?

Regards,

Michele

7245.page1.pdf

  • 0
    TI__Mastermind 24075 points

    Hi Michele,

       I cannot see the time scale in those photos. BQ24650 has battery absent detection in which the output voltage dips, as the IC sinks and sources current to detect if the battery is there. Is the battery connected during your testing? If the dips are 500ms apart, then this is the IC performing battery absent detection and is expected behavior when battery is absent. By "load" are you referring to a CC load sinking the current values mentioned above?

  • 0 in reply to Kedar Manishankar
    Prodigy 110 points

    Hello Kedar,

    thanks for the quick reply. 

    The waveforms were taken with an elctronic load, but they were quite similar with the battery connected.

    We have found that there was an incorrect resistance value on the board, something went wrong during the assembly process.

    Now the circuit works as expected. 

    Thanks for the support.

    Michele