BQ24780S: About circuit constants

Hi Tomoya,

I found your questions are related to the schematic. We have a schematic review checklist. Hope this helps. 

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1064617/faq-bq24780s-faq-how-do-i-ensure-the-charger-schematic-is-satisfactory-is-there-a-schematic-checklist-for-bq24780s

Regards,

Tiger

Hi Tiger,

Thank you for your answer.

Sorry, this schematic alone did not solve everything.
Could you please answer each question on the excel sheet?

Thanks and best regards.

Tomoya Yoshino

Hi Tiger,

【R17】

【R20、R21】

【R26、R27、R29】

This schematic does not have the above description.

Thanks and best regards.

Tomoya Yoshino

Hi Tiger,

【R12、R13、R28】　3.9 kΩ（5%）OK?

Do HIDRV and LODRV need Current-limiting resistors?

Thanks and best regards.

Tomoya Yoshino

Hi Tomoya,

TI suggests following our EVM schematic as much as possible. The schematic has been validated in the product development, and been used by many other customers. I don't see any reason to change or deviate from our standard practice. 

Regarding your specific questions, it is probably Okay to use 3.9K, but we don't endorse this change.  No additional gate resistance is needed for HIDRV and LODRV. 

Regards,

Tiger

Hi Tiger,

Thank you for your answer.

【R26、R27、R29】

This schematic does not have the above description.

Would it be better to use 10Ω as damping resistance?

【R7、C12】

I don't understand these effects, can you explain them?

Thanks and best regards.

Tomoya Yoshino

Hi Tiger,

【Q1、Q2、Q3、Q4、Q5】

Would you recommend putting resistance (Rgs) between the gate and source of the MOSFET?

【Q4】

Would you recommend putting snubber circuit between the drain and source of Q4?

Thanks and best regards.

Tomoya Yoshino

Hi Tomoya,

The Rgs resistor is unnecessary. We have a RC snubber on the switch node, which is sufficient for the voltage spike suppression. 

Regards,

Tiger

Hi Tiger,

Thank you for your answer.

【R26、R27、R29】

This schematic does not have the above description.

Would it be better to use 10Ω as damping resistance?

【R7、C12】

I don't understand these effects, can you explain them?

Thanks and best regards.

Tomoya Yoshino

Hi Tomoya,

We already use 10-ohm. R7 and C12 work with the ACFET to limit the inrush current.

Regards,

Tiger