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.
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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
