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BQ25703A: Resistor Value at IADPT pin when using 1.5uH

Shinichi Inoue
Guru 21566 points
Part Number: BQ25703A

Dear Specialists,

My customer is considering BQ25703A and has a question.

I would be grateful if you could advise.

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I am considering a resistor at IADPT pin.

I'd like to use 1.5uH inductor, what ohm should be used?

According to the datasheet P.25, Table 3., it only described 1uH, 2.2uH and 3.3uH.

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I appreciate your great help in advance.

Best regards,

Shinichi 

  • 0
    TI__Genius 16125 points

    Shinichi,

    In general, we didn't recommend to use 1.5uH inductor. Is it possible to stay with 2.2uH?

    Thanks

  • 0 in reply to Paul Yeh
    Guru 21566 points
    Hi Paul,

    Thank you for your reply.

    I understand 1.5uH is not recommend.

    I'd like to know the reason why 1.5uH is not reccomend to explain to the customer.

    I appreciate your great help.

    Best regards,

    Shinichi
  • 0 in reply to Shinichi Inoue
    TI__Expert 5330 points

    Hi Shinichi,

    The pin is sampled at startup and the inductor value specified is used to reconstruct inductor current (it is sensed at the switch, so only rising inductor current can be directly measured.).  The inductor value used for reconstruction is not linearly related to the resistor value, instead the resistor value is latched into one of the three bins specified in the datasheet, i.e. 1.0, 2.2, 3.3 uH.  If you use a different inductor value than one of these three, it will incorrectly reconstruct the inductor current and this will adversely affect the feedback circuit.

    Regards,

    Steve

  • 0 in reply to Steve Preissig
    Guru 21566 points

    Hi Steve,

    Thank you for your reply.

    I understand inductor should be selected from 1uH, 2.2uH or 3.3uH, not used other inductor.

    Could you please advise, 1.5 μH is stated in the data sheet P.36 as the inductance value at the switching frequency of 1.2 MHz.

    Is it possible to think of this description as a mistake in description?

    I appreciate your great help.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Expert 5330 points
    Hi Shinichi,

    I spoke to our systems engineer about this reference of 1.5 uH on P.36 and he informs me that this reference to 1.5 uH will be removed from the datasheet in the next revision.

    Regards,
    Steve
  • 0 in reply to Steve Preissig
    Guru 21566 points

    Hi Steve,

    Thank you for your reply.

    I understand 1.5uH will be removed in the next version.

    I'll share this information with the customer.

    I appreciate your great help.

    Best regards,

    Shinichi