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BQ24297: Capacitor and Inductor Selections

Chris Lange
Prodigy 70 points
Part Number: BQ24297

In regards to the values of the required capacitors and inductor, is there a range of values and/or equations to calculate values for this part?

Specifically:

  1. Can the bootstrap capacitor (SW to BTST) be any value other than 0.047uF?  Like 1uF?
  2. Can the REGN capacitor (REGN to analog GND) be any value other than 4.7uF?  Like 10uF?
  3. Can the VBUS capacitor be larger than 1uF? Like 10uF?
  4. Can the inductor be 4.7uH if sized properly according to 10.2.2.1 Inductor Selection in the datasheet and according to the following excerpt under 10.2.2.3?

The charger device has internal loop compensator. To get good loop stability, the resonant frequency of the
output inductor and output capacitor should be designed between 15 kHz and 36 kHz. The preferred ceramic
capacitor is 6 V or higher rating, X7R or X5R.

  • 0
    TI__Guru 57321 points
    Hi,

    The charger device has a type III compensation network which allows using ceramic capacitors at the output of the converter. The output inductor and output capacitor selection is limited to ensure good system stability: the resonant frequency of the output inductor and output capacitor should be designed between 15 kHz and 36 kHz.

    1. Fixed 0.047uF
    2. Fixed 4.7uF.
    3. Yes.
    4. Not recommended.

    Thanks,

    Ning.
    Please click "This Resolved my issue" button if this post answer your question.
  • 0 in reply to Ning T
    Prodigy 70 points
    Can you comment as to the selection of the 2.2uH inductor used in the bq24297EVM?
    Also, can you comment on the slew rate resistor R1? Is there documentation to set slew rate?
  • 0 in reply to Chris Lange
    TI__Guru 57321 points
    Hi,

    2.2uH inductor was popular when the device was released.

    BTST resistor (R1) is not required. It may help to improve EMI when needed.

    Thanks,

    Ning.
    Please click "This Resolved my issue" button if this post answer your question.