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BQ24650EVM-639: Increased my VBat/Vout, suddenly not charging

Marianne Fatima Valenzeuela
Prodigy 50 points
Part Number: BQ24650EVM-639

I have changed my R13 (from 499k to 330k) and R15 (100k to 56k) to increase my voltage to 14.4V. On my first try to charge a LiFePO4 battery, the charge current suddenly dropped to almost 0A upon reaching 0.8A, please see graph below. When I checked my VFB voltage, it is just 11mV -- I suppose it should be 2.1V. I'm pretty sure that the resistors are properly soldered. The 11mV actually voltage divides between R13 and R15. Also, during the first 1.5hrs of charging, my VBat/Vout is 14.4V then after the current drop, it became 80mV. The Vsys, and all other test points are as it should be. 

Before doing all the changes, the EVM does work fine. I just really wanted to charge my 12V battery as it maximum capacity. Hence, the increasing of VBat/Vout.

  • 0
    TI__Mastermind 40375 points

    Hello,

    What is your battery voltage throughout this charging period? Do you have a graph for it as well? If your battery voltage is truly 14 V, the FB divider should not be 11 mV. What is the FB voltage when you are charging the battery normally?

    What is the input voltage you gave to the EVM?

    For your battery voltage to suddenly go from 14.4 V to 80 mV there has to be a massive discharge event.

    Can you please provide a waveform of the input voltage, PH voltage, output voltage, and output current when the expected and unexpected behavior are happening?

    Thanks,

    Mike Emanuel