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BQ24250: The Range of Capacitance value of Cboot

Shinichi Inoue
Guru 21566 points
Part Number: BQ24250

Dear Specialists,

My customer is considering BQ24250 and has questions.

I would be grateful if you could advise.

---

According to the datasheet, Cboot is recommended to use 0.033uF 15V rating, but it is difficult to obtain because of long delivery time.

So, could you please tell me following two questions. 

(1) 

If a 0.047 uF or 0.022 uF capacitor is used for Cboot, one is larger, another is smaller.

What kind of concern are there?

What is the range of the capacity value of Cboot?

(2) 

Regarding the Cboot, the datasheet is specified as rated voltage is 15 V or more,
I am planning to use a capacitor with a voltage rating of 16 V from the point of availability.

What kind of concern are there by using capacitors with voltage rating of 16V?

---

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Guru**** 165786 points
    Shinichi,

    We only tested with 25-V rated CBOOT=0.033uF and so cannot warranty other values. Using too high of value could result in the capacitor not being fully recharged during switching, and therefore, the gate driver has difficulty turning on the high side FET. Using too low of a value could result in needing more frequent recharge pulses and lower effective maximum duty cycle. As you know, ceramic capacitor capacitance values drop as their applied voltage reaches their rated voltage. Therefore, if you use a 0.047uF 16-V rated capacitor with VIN=5Vmax, it will likely de-rate close to 0.033uF, resulting in similar operation as with CBOOT=0.033uF.
  • 0 in reply to Jeff F
    Guru 21566 points
    Hi Jeff,

    Thank you for your reply.

    I'll share your suggestion with the customer.

    If he has an additional question, I consult you again.

    I appreciate your great help.

    Best regards,
    Shinichi