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bq24257 LDO

Jonathan Bischof
Prodigy 60 points
Other Parts Discussed in Thread: BQ24257

Hi community


I'm designing a charging circuit using the bq24257 switching charger.

The bq24257 has a built-in LDO which is supposed to put out 4.9V. The bq24257 however is specified to run from 4.35V to 6.5V.

I'm planning to use the bq24257 at 4.7V supply voltage. What is going to happen to the LDO in this case?

I suppose it won't be able to put out 4.9V but rather 4.4..4.5V.

Will that have an impact on any of the functions of the bq24257, such as temperature sensing or the charging circuit itself?

Thanks for any help!

regards,

Jonathan

  • 0
    TI__Genius 13700 points

    Hello Jonathan,

    The LDO internal to the BQ24257 will operate much like any other LDO when the input voltage is less than the designed regulation voltage by outputting the input voltage less the drop out voltage .

    The temperature sensing will scale with the output voltage of the LDO since the thresholds are determined by internal resistive dividers.

    Otherwise the LDO is also used to detect the battery by biasing the BAT pin which as long as the output of the LDO is high enough to bias any protection circuitry that might be between the charger and the battery otherwise this should be fine.


    The last thing the internal diagram shows the LDO is used for is the assist in the bootstrap supply for the high-side FET.

    All of this to say that device should work with a lower voltage since it has a recommended operating range down to 4.35V as long as the battery regulation is sufficiently below the input voltage.