• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 62 subscribers
  • Views 172 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS563231: Confirmation Request how to calculate Rboot

Shinichi Inoue
Guru 20311 points
Part Number: TPS563231

Tool/software:

Dear Specialists,

My customer is considering TPS563231 and has a question about Rboot.

I have considered the value of Rboot.

Please confirm the listed below.

I have focused on the rise time, I think the result may be too conservative.

I would like you to some advice on the possible values ​​of Rboot.

---

One period of 600kHz is 1/600kHz=1.67μs.

Vin:5V

Vout:3.3V

Iout:3A

When used with 5Vin 3.3Vout, the ON duty is Vout/Vin＝3.3V/5V=0.66

The OFF duty is 0.34, which is 0.56μs.

The boot capacitor is charged during the OFF time.

It needs to be fully charged during 0.56μs.

The time constant is CR×2.3, since it takes 63.2% of the rise time, considering that it rises to about 90% during the OFF time.

CR×2.3＜0.56μs

R＜2.4Ω

The maximum value of Rboot is 2.4Ω.

This calculation is based on the assumption that Cboot rises from 0 to 90% with each switching cycle.

Since Cboot never actually becomes 0, I think Rboot can take a slightly larger value.

Please let me know how to calculate and how many ohms it can be used up to..

ｰｰｰ

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Genius 9070 points

    Hi Shinichi,

    Usually, Rboot is not a calculation value because Rboot is used to adjust SW voltage rising slew rate in order to decrease noise and EMI. So usually Rboot is decided in actual test.

    You can see this APP note to learn more about Rboot. Thanks.

    snvaa73.pdf

    Best Regards,

    Shipeng

  • 0 in reply to Shipeng Cheng
    Guru 20311 points

    Hi Shipeng,

    Thank you for your reply.

    I've already seen the application note you suggested,

    This application note describes a situation where Vboot decreased due to the RC time constant and parasitic inductance.

    In this case, the customer would like to use Rboot(10ohm) and Cboot(0.1uF).

    Is there any problem to use Rboot(10ohm) and Cboot(0.1uF).

    In some cases, the resistance value is limited, I'd like to confirm.

    Are the time constants of Rboot(10ohm) and Cboot(0.1uF) too large?

    I appreciate your great help and cooperation. 

    Best regards,

    Shinichi

  • +1 in reply to Shinichi Inoue
    TI__Genius 9070 points

    Hi Shinichi,

    I think 10ohm is acceptable.

  • +1 in reply to Shipeng Cheng
    Guru 20311 points

    Hi Shipeng,

    Thank you for your reply.

    I'll share 10ohm is acceptable with the customer.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi