BQ24297: EMI

Takashi Yamaguchi

Part Number: BQ24297
Other Parts Discussed in Thread: TPS61169

Hi team,

My customer is evaluating the bq24297 in their system. They have been conducting an noise emission test with their board which integrated bq24297 and TPS61169(LED driver) . The customer says that they see large noise emissions at 50 to 70 MHz and 150 to 200 MHz, and that they are taking action, but they are not able to reduce the noise. They say that disabling the TPS61169 did not cause any change in the noise emissions. Therefore, this noise seems to be generated by bq24297. Also, when the customer stopped the charging and supplied the power from battery, the noise emission was reduced, so the DC/DC switching operation of bq24297 converter may affect to the noise emission. The input power source is USB 5V.

Do you have any countermeasure for the noise emission? If the bq24297 setting prevents this noise emission, could you tell me it?

Regards,

Yamaguchi

over 3 years ago

0 Ning T over 3 years ago

TI__Guru 51991 points

Yamaguchi,

Please refer to https://e2e.ti.com/support/power-management/f/power-management-forum/918939/bq25895-emi-emc for some suggestions.

Thanks,

Ning.

0 Takashi Yamaguchi over 3 years ago in reply to Ning T

TI__Genius 12150 points

Hi Ning,

Thank you for your support. I let the customer know the E2E thread.

I received some questions about the suggestion in the E2E. Could you please advise me about the following questions?

#2.Slower SW node switching slew rate

--> Could you please let me know the recommended resistor value or start point value between BTST and SW? (The customer is currently using a 0.047uF capacitor for BTST. The customer thinks that the time constant of the CR series circuit should be a time constant that has little effect on the switching frequency of 1.5MHz. For example, if the customer sets it to 15MHz, it will be about 0.2Ω. Is this okay? ..)

#4.Use EMI bead to reduce EMI

-->The customer has already put beads on the VBUS line. Does putting beads in the PMID line mean putting beads in series with the capacitor connected to PMID?

Regards,

Yamaguchi

0 Ning T over 3 years ago in reply to Takashi Yamaguchi

TI__Guru 51991 points

Yamaguchi,

#2 Please try various BTST resistance to get the best result. The BTST resistance should not be more than 5ohm.

#4 VBUS and PMID are shorted via RBFET in charge mode.

Thanks,

Ning.

0 Takashi Yamaguchi over 3 years ago in reply to Ning T

TI__Genius 12150 points

Hi Ning,

Thank you for the answer. Regarding the answer #4, since VBUS and PMID are shorted via RBFET in charge mode, does that mean that a bead on VBUS line is enough?

Regards,

Yamaguchi

0 Ning T over 3 years ago in reply to Takashi Yamaguchi

TI__Guru 51991 points

Yamaguchi,

EMI performance is heavily dependent on the system design, board layout etc. It is better to try on the customer boards and optimize the EMI performance.

Thanks,

Ning.

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BQ24297: EMI