BQ76200: Noise in capacitors

Achim Wack

Part Number: BQ76200
Other Parts Discussed in Thread: BQ78350, , BQSTUDIO, EV2400

Hi,

we run several projects with BQ7694000, BQ78350 and BQ 76200. Some PCBs have the strange phenomena, that the capacitors on VDDCP make a ticking noise. When I touch the capacitors on the VDDCP side the noise disappears.

The actual configuration with this phenomena (only one PCB of three): BQ76200 with 12 DSG FETs and 12 CHG FETs (IPTC007 / Infineon) and three 1,5µF MLCC 100V capacitors in parallel. I also tried a fourths capacitor with no change.

Best regards,

Achim

over 1 year ago

0 Luis H. S. over 1 year ago

TI__Mastermind 42060 points

Hello Achim,

That is strange.

Do you have any waveforms of the pin of the board with the ticking noise and board without the noise?

Best Regards,

Luis Hernandez Salomon

0 Achim Wack over 1 year ago in reply to Luis H. S.

Prodigy 230 points

Hi Luis,

yes, it´s really strange. I´ve to measure again with the scope, but I was also wondering that I can´t see any spikes when I measured first a few days ago.

But I´ve made an additional observation: When switching the FETs manually with BQStudio the ticking was only when switching on the DSG MOSFET, not when switching on the CHG MOSFET.

Best regards,

Achim

0 Luis H. S. over 1 year ago in reply to Achim Wack

TI__Mastermind 42060 points

Achim,

To confirm, the ticking is coming directly from the VDDCP capacitor correct? Is it all three?

Have you tried replacing the capacitor? To get rid of any doubts that it could be a faulty cap.

What do you mean by "I can't see any spikes"?

Best Regards,

Luis Hernandez Salomon

0 Achim Wack over 1 year ago

Prodigy 230 points

Hi Luis,

I just did some scope measurements, see attachment.

A further observation I did: I can switch on manually both FETS in bqStudio. Even when I close both FETs are onm. As soon as I disconnect EV2400 the CHG FET switches off after some seconds and ticking stops. When I connect SMB again, CHG switches on again and ticking begins.

Best regards,

AchimBQ76200.zip

0 Luis H. S. over 1 year ago in reply to Achim Wack

TI__Mastermind 42060 points

Hello Achim,

What exactly is being shown in the waveforms?

Can you share your schematic also? So we can check all looks okay.

Best Regards,

Luis Hernandez Salomon

0 Achim Wack over 1 year ago in reply to Luis H. S.

Prodigy 230 points

Hi Luis,

yes I have. Thought that I´ve attached it... Seems to be failed... I hope it works now. All three pictures are measured at the BQ76200

Achim

0 Achim Wack over 1 year ago in reply to Achim Wack

Prodigy 230 points

Sorry, I´ve read an older message from you. Please find attached the schematics.0532E.0X0_SCH.PDF

0 Luis H. S. over 1 year ago in reply to Achim Wack

TI__Mastermind 42060 points

Hello Achim,

I am not entirely sure what you are showing in these images, is the VDDCP capacitor dropping in voltage periodically as shown? Is this when you switch ON a FET?

The schematic looks okay, although D32/R74 should be directly connected between DSG and PACK. D32 should also be a larger Zener than D31.

How many FETs are you using? I'd recommend reading Section 6 VDDCP Capacitance Reference Table of the FET Configurations for the bq76200 application note. The following table (found there), can be used as reference:

Best Regards,

Luis Hernandez Salomon

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BQ76200: Noise in capacitors