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bq24650 - Poor line regulation

Matthew Day
Mastermind 36110 points
Other Parts Discussed in Thread: BQ24650

I'm using the bq24650 EVM to charge a 7.2V sealed lead acid battery.  I've noticed the charge current increases over 10% as I increase the input voltage from 15V to 25V.  Why is the charge current not constant with changing input voltage?

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    TI__Genius 17340 points

    We have observed that the accuracy of the average current sensor degrades when the inductor current ripple is too large compared to the average current.  This becomes more pronounced as the input voltage increases because inductor current ripple is directly proportional to the input voltage.

    The solution is use the recommended inductor in the datasheet for the given charging current. See the section "INDUCTOR, CAPACITOR, AND SENSE RESISTOR SELECTION GUIDELINES" in the datasheet and the recommended values in Table 1. If you're changing the inductor, remember to change the output capacitor to keep the LC resonant frequency within the recommended range (12kHz to 17kHz) to keep the system stable.

    Regards,
    Matt Guibord