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bq24616 input capacitor?

Zhang Hui
Intellectual 625 points
Other Parts Discussed in Thread: BQ24616

Hello,

In bq24616 datasheet there is a section “input capacitor”, "A 25-V rating or higher capacitor is preferred for 20-V input voltage. A 10-µF to 20-µF capacitance is suggested for typical of 3-A to 4-A charging current."

Both C16 and C8 are on the input size, one for adapter and another for near switching MOSFETs Q4 and Q5. Which one is the “input capacitor”?

 

Hui

  • 0
    TI__Expert 5565 points
    The input capacitor in this diagram is C8. Capacitor C16, in combination with R20, is a snubber circuit for hotplug events on the adapter.
  • 0 in reply to Smriti B
    Intellectual 625 points

    Dear Smriti,

    “A low-ESR ceramic capacitor such as X7R or X5R is preferred for the input decoupling capacitor and should be placed as close as possible to the drain of the high-side MOSFET and source of the low-side MOSFET.”

    What we still find confusing is the indefinite article “A” suggest there is only one (or one set) of such capacitor, yet it should be placed both close to (drain of high MOSFET) and (source of low MOSFET). Does it actually mean: C8’s positive near Q4(high MOS)’s drain, and C8’s negative near Q5(low MOS)’s source?

    In addition, could the Gerber file of HPA422 be added to the EVM’s page, or forum?

     

    Hui

  • 0 in reply to Zhang Hui
    TI__Expert 5565 points

    Hui,

    Yes, the single capacitor should be placed close to the drain of the high side FET and the source of the low side FET. This ensures that the AC loop is kept as small as possible so that ringing and noise is kept to a minimum. See Figure 21 of the datasheet (image below) as well as the layout of the EVM (image below). Notice how Q3 (high side FET) and Q4 (low side FET) are stacked so that it allows for C10/C11 (input capacitors) be placed close to both Q3 and Q4.