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BQ24040: Asking for BQ24040 high current, Vin and VS output current

SHH
Mastermind 32196 points
Part Number: BQ24040

Hi team,

Customer is designing BQ24040 as the charger IC in our design. It is working as expected with normal charging current (<500 mA).

 

The behavior customer would like to clarify is when customer set a higher charging current (1 A).

In that specific case, customer can see that the charging current depends quite a lot on the input voltage.

But even with an input voltage above IN_DPM (4.4V), the output current varies (see picture below, right plot, current not stable): 

would you please review and provide comment?

 The closest guess is that the voltage dropout across the IC must be high enough with high output current to satisfy the output current setting.

But customer has not found much info on that on the DS.

Here is the corresponding dropout:

 

Would you be able to confirm / disprove customer guess, and therefore tell us about what would be the implication regarding the charging process ?

BR,

SHH

  • 0
    TI__Mastermind 19195 points

    Hello SHH,

    The device is a linear regulator so this is the expected behavior when setting it the max charge current. We provide a VDO parameter here in the datasheet: 

    If you don't want any current reduction you should have Vin - Vout > 500mV. The device may take slightly longer to reach the CV phase if in drop-out. Termination is unaffected.

    Best regards,

    Nick

  • 0 in reply to Nick Brylski
    TI__Mastermind 32196 points

    Hi Nick,

    Thank you for the explanation. Dropour seems to be the route cause indeed. And great to hear that termination is unaffected.

     The datasheet indeed specifies that the dropout needs to be greater than 500 mV.

    But if you look at the following chart (output current VS measured VDO), customer got dropout voltage greater than 500mV although we can't reach 1A current.

    customer actually found out that in the VDO test condition in the datasheet, the charger is set for 1A output current but the current drops down to 0.5 A when we reach a dropout of 325 mV to max 500 mV.

     

    What would be a safe dropout condition to ensure max output current near 1A (500 mV seems not enough) ? 

    BR,

    SHH

  • 0 in reply to SHH
    TI__Mastermind 19195 points

    Hello SHH,

    The parameter we provide is tested with condition of 500mA, for 1A you are correct 500mV may not be enough. For 1A to see no dropout I would supply at least 1V above Vbat max (5.1-5.2V).

    Best regards,

    Nick