BQ25710: Can 1nF capacitor be placed at PSYS?

Koyo Asaishi

Intellectual 1930 points

Part Number: BQ25710

Hello team

Customer want to add 1nF capacitor at PSYS which is close to IMVP9 controller. Is thre any concern?
My concern is inrush current, charging time, over voltage etc.

Best regards
Koyo

over 1 year ago

+1 Md Munir Hasan over 1 year ago

TI__Expert 3335 points

Hi Koyo,

The purpose of the capacitor is filtering at PSYS pin. A higher cap would introduce a longer settling time. The typical cap value we use for PSYS pin is 100pF. Although a higher value of capacitor should not be a concern, we have not tested 1nF. What is the purpose of using 1nF on the IMVP9 controller side? to minimize noise due to long wire trace?

Best Regards,

Munir

0 Koyo Asaishi over 1 year ago in reply to Md Munir Hasan

TI__Intellectual 1930 points

Hi Munir

Thank you for prompt answer.
IMVP controller side recommend to add a capacitor for noise.

Best regards
Koyo

0 Md Munir Hasan over 1 year ago in reply to Koyo Asaishi

TI__Expert 3335 points

Hi Koyo,

I received a confirmation on the large cap on PSYS. We don' t recommend increase the cap on PSYS as it might affect the stability of the internal current source. If they are concerning about noise, you can add RC filter instead. If any issue arises afterwards let us know.

Best Regards,

Munir

0 Koyo Asaishi over 1 year ago in reply to Md Munir Hasan

TI__Intellectual 1930 points

Hi Munir

Do you mean 100pF is safe to use for PSYS but 1nF is not recommended?
If RC filter is better, can you share the resistor value (RIMVP)?

Best regards
koyo

0 Md Munir Hasan over 1 year ago in reply to Koyo Asaishi

TI__Expert 3335 points

Hi Koyo,

Yes 100pF is safe. But 1nF may affect the stability. An acceptable value would be 10 Ohms. You can use the filter as below. Put the 100pF for the BQ25710 close to the charger. Then use 100pF for the RC filter close to IMVP.

Best Regards,

Munir

0 Koyo Asaishi over 1 year ago in reply to Md Munir Hasan

TI__Intellectual 1930 points

Hi Munir

1000pF is the recommendation from IMVP vender.
How about below block?

Time constant of Rimvp and the cap is same as your recommendation.

0 Md Munir Hasan over 1 year ago in reply to Koyo Asaishi

TI__Expert 3335 points

Hi Koyo,

That should be fine.

Best Regards,

Munir

0 Koyo Asaishi over 1 year ago in reply to Md Munir Hasan

TI__Intellectual 1930 points

Hi Munir

Why is Rimvp required?
If the 1000pF make it possible to be unstable, Rivmp won't help to resolve.

0 Md Munir Hasan over 1 year ago in reply to Koyo Asaishi

TI__Expert 3335 points

Hi Koyo,

Thanks for asking. The reason for not adding 1nF was that it may result in slow response on PSYS pin voltage. The dominating time constant is still determined by the PSYS pull down resistor and additional 1nF. However, after raising this issue again with design team they feel confident to use 100pF+1nF as well. Therefore, the Rivmp can be removed. We will be allowing 1nF for IMVP in our future checklist given that the customer would like to accept the extra delay due to 1nF cap. The risk of stability issue is very low.

Best Regards,

Munir

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BQ25710: Can 1nF capacitor be placed at PSYS?