BQ79616-Q1: Buzzing noise caused by communication in stacked configuration

Jeffrey Uitbeijerse

Part Number: BQ79616-Q1
Other Parts Discussed in Thread: BQ79600-Q1, , BQ79616

Tool/software:

Hello,

I have designed a custom PCB with a single BQ79616-Q1 balancing chip. The configuration in my test setup is 2 BQ79616-Q1 in a stack, communicating through a BQ79600-Q1 with a MCU (F280049) using SPI. Auto-addressing and waking the devices is successful, and I can read voltages and temperatures correctly.

However, I notice a buzzing sound coming from the PCBs with the BQ79616 devices. The frequency of this buzzing noise seems to depend on the rate with which I try to read the cell voltages, since requesting the data once every second produces a 'tick' every second, and increasing this rate to 100 times per second produces a buzzing noise.

Some things I noticed:

Connecting only 1 BQ79616 device in my stack eliminates the sound. The sound is only produced when connecting a second device to the stack, and in that configuration both PCBs produce the buzzing sound.
The daisy chain circuit is designed with capacitor and choke isolation, using recommended components mentioned in SLVAEP4. Removing the chokes on one PCB decreases the volume of the produced sound, but does not remove it completely.
I found a thread which describes a similar observation: BQ79616-Q1: hear the buzzing sound when BQ79616-Q1 communicating - Power management forum - Power management - TI E2E support forums

Is this observation expected behaviour? Can it cause any harm or decrease in lifetime of the components? Is there a way to remove the sound? Thanks for the help.

Regards, Jeffrey

4 months ago

0 Pranav Ananthan 4 months ago

TI__Intellectual 1395 points

Hi Jeffery,

This has been observed before, according to the forum post you have linked, but is not expected behavior at all. This noise could possibly be due to improperly soldered components, as removing these components has been shown to work, to some extent, based on yours and the other user's information.

Thank you for your question,

Pranav Ananthan

0 Jeffrey Uitbeijerse 4 months ago in reply to Pranav Ananthan

Prodigy 50 points

Hi Pranav Ananthan,

I found another post describing the same problem (BQ79616: BQ79616 LDOIN cap buzzes - Power management forum - Power management - TI E2E support forums). Since three different cases have already been reported, and the buzzing noise persists after changing PCBs several times, I highly doubt it has to do with improperly soldered components.

The post I linked suggests to change capacitor from X7R to C0G, and use two 100nF caps instead of one 0.22uF cap. Do you have any other suggestions that could remove the sound?

Regards,
Jeffrey

0 Pranav Ananthan 4 months ago in reply to Jeffrey Uitbeijerse

TI__Intellectual 1395 points

Hi Jeffery,

This buzzing noise occurs when communication occurs, so it makes sense that it happens when having multiple devices in a stack.

I agree, with that information, it is likely not due to improperly soldered components.

Based on information from those other customer experiences, changing the capacitor, or using two capacitors in parallel, has been shown to work. Additionally, depending on the system, removing the capacitor would also be an option.

Thank you,

Pranav Ananthan