TPS53515: About Vbst pin

Tsukui Yusuke

Guru 21930 points

Part Number: TPS53515

Hi,

Customer considering bst resistor to suppress ringing.

Customer want to know the current flowing to Vbst pin and Vbst pin voltage in order to know the required bst resistor specifications.
Could you give me advice on how to choose the Vbst resistor?

Best Regards,
Yusuke/Japan Disty

over 8 years ago

0 JohnTucker over 8 years ago

TI__Guru**** 191445 points

Recommended BST resistor for TPS53515 is 3 ohm. Here is some useful material concerning it:
e2e.ti.com/.../the-effects-of-gate-driver-strength-in-synchronous-buck-converters

0 Vental Mao over 8 years ago

TI__Expert 5745 points

Generally， The purpose of the resistor in series with the BST cap is not to limit this charging; we would not want to do that. The BST resistor can help limit the SW node positive ringing by slowing down the charging of the high-side power FET’s gate-source voltage. So choose the resistor which is meet your ring limit

0 Tsukui Yusuke over 8 years ago in reply to Vental Mao

Guru 21930 points

Vental-san,John-san

Thank you for you support.
I understood how to choose the resistor value.
Let me ask you one more thing.
Customer wants to know the rated power (size) of resistance to be installed.
Could you give me your advice?

Best Regards,
Yusuke/Japan Disty

0 Vental Mao over 8 years ago in reply to Tsukui Yusuke

TI__Expert 5745 points

The 1/4 W is enough. There is no large power loss through the resistor

0 Tsukui Yusuke over 8 years ago in reply to Vental Mao

Guru 21930 points

Vental-san,

Thank you for you kind support.
Please tell me the recommended capacitor rated voltage?
Customers are trying to use a 25V rated voltage products.
Do you have any problems with 25V rated voltage?

Best Regards,
Yusuke/Japan Disty

0 JohnTucker over 8 years ago in reply to Tsukui Yusuke

TI__Guru**** 191445 points

For VBST, the capacitor is charged via VREG relative to the SW node, so 25 V should be more than enough. If you want to protect against the ABS MAX voltage rating for VBST (36 V), then a 50 V rating would be required. THE VBST capacitor should never see that voltage during normal operation.

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TPS53515: About Vbst pin