BQ76940: BMS battery cells proper connection

Robert Nunez

Part Number: BQ76940

Good day, I would like to ask if this is the proper orientation when I connect my 9S battery pack to the BMS board:

I used http://www.ti.com/lit/df/tidr773/tidr773.pdf as reference and here is my schematic file /cfs-file/__key/communityserver-discussions-components-files/196/1121.Schematic.rar I ask this because I tried to connect the battery cells this way, and couldn't power up the AFE and MCU.. after checking my board, it turns out that diode D19 has broken. I can see a hairline crack in the surface, and a connection test shows it as a short.

What could have been the reason this diode failed? I know that it was previously working, as when I didn't have my 9S battery pack yet, I can power up the AFE and MCU using a 9V source and three 220 ohm resistors to simulate the lower group of cells like this

Thank you very much,
Robert

over 5 years ago

0 Matt Sunna over 5 years ago

TI__Guru* 80963 points

Hi Robert,

I checked your schematic and I do not see any issue that would explain the failure you observed. The diode is rated for high enough voltage that your 9-cell battery should not have caused it to fail. It is possible that there are transients when you connect the battery. This might be good to capture on a scope. It would also be good to review the Random Cell Connection section of this app note: http://www.ti.com/lit/an/slua749a/slua749a.pdf to see if there are any clues as to what might be occurring.

Best regards,

Matt

0 Robert Nunez over 5 years ago in reply to Matt Sunna

Intellectual 570 points

Thanks Matt, I'll check that document.

And another quick question, would the board consume power if the battery pack is connected to the VCx pins, but not to BAT+/- such as this?

0 Matt Sunna over 5 years ago in reply to Robert Nunez

TI__Guru* 80963 points

Hi Robert,

I expect it likely will. The power supply pins will still get power through the components on the board. This would also mean that cells are connected without VSS being connected. VSS should always be connected first to avoid damage.

Matt

0 Robert Nunez over 5 years ago in reply to Matt Sunna

Intellectual 570 points

Thanks for the reply! VSS, meaning the negative terminal of the battery, right? Maybe that's what went wrong. I connected the cells first before VSS.

0 Matt Sunna over 5 years ago in reply to Robert Nunez

TI__Guru* 80963 points

That's correct. VSS should always be connected first.

I hope this solves the issue,

Matt

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BQ76940: BMS battery cells proper connection