BQ76942: CUDEP protection, FET fail, FUSE and Permanent Fail

Attila Dányádi

Part Number: BQ76942
Other Parts Discussed in Thread: BQ76952

Dear TI support,

My issue is very similar to this topic:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1050662/bq76942-fuse-blow-condition?tisearch=e2e-sitesearch&keymatch=BQ76942#

I would like to blow the fuse when CFETF or DFETF fail occours. I also would like to implement recharge protection when a cell voltage less then 2V on wake up from SHUTDOWN using CUDEP protection.

The settings below are not enough to blow the fuse on FET fail (DFETF, CFETF, PF_FETS, FETF_FUSE), also PF_FUSE should be set.

Since this point every enabled PF will drive the fuse.

So on the manufacturing line when BAT- and BAT+ connected/soldered/welded (should before connecting other cells VC1-VC9) the CUDEP is activated and fuse will be driven.

How I can prevent this?

Thanks in advance,

Attila

cudep_2.gg.csv

over 2 years ago

0 Matt Sunna over 2 years ago

TI__Guru* 78533 points

Hi Attila,

The Permanent Fails are not enabled by default on the BQ76952. Are you planning to program the OTP in production to enable permanent failures by default? Here is an FAQ on the OTP feature: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1082914/faq-bq76952-common-questions-for-otp-programming-with-the-bq769x2-device-family

If you are not programming the OTP in production, the microcontroller can configure all of these registers at system startup after all of the cells are already connected. If you are planning to program OTP in production, then maybe you can set PF_EN = 0 in OTP and then send the PF_ENABLE() command from the microcontroller at power-up. This way the permanent fail will not cause an issue while connecting the cells.

Best regards,

Matt

0 Attila Dányádi over 2 years ago in reply to Matt Sunna

Prodigy 100 points

Hi Matt,

Yes I do want to enable the permanent failures by default in OTP. We have microcontroller outside the battery pack, so enabling PF by microcontroller can be a solution. But by this way the battery pack is not safe (no secundary protection) in stand alone mode.

Any other workaround?

BR,

Attila

0 Matt Sunna over 2 years ago in reply to Attila Dányádi

TI__Guru* 78533 points

Hi Attila,

When do you wake up the device? It should be in Shutdown mode until you wake the device with the TS2 pin or LD pin, so you should be able to connect the cells without risk of a PF I think.

Regards,

Matt

0 Attila Dányádi over 2 years ago in reply to Matt Sunna

Prodigy 100 points

Hi Matt,

The device configured to go Shutdown under 27.5V stack voltage and wake up via LD (charger detect).

The problem is CUDEP activated on power up as well, not only wake up from shutdown.

Best regards,

Attila

0 Matt Sunna over 2 years ago in reply to Attila Dányádi

TI__Guru* 78533 points

Hi Attila,

Would it be possible to set the CUDEP delay a little longer and to hold the RST_SHUT pin high when BAT+ is connected to put the device into Shutdown? Or can the connection order be modified to connect the cells and BAT+ last?

Regards,

Matt

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BQ76942: CUDEP protection, FET fail, FUSE and Permanent Fail