BQ40Z50-R1: Battery safety certification issue

Ravid BY

Part Number: BQ40Z50-R1
Other Parts Discussed in Thread: BQ29610

Hi,

Our battery was sent to a safety lab for IEC62368. The guy at the lab told us that we cannot pass IEC62368 with the current battery design that includes the BQ40Z50-R1.

In the EV board there is a chemical fuse that can be triggered by the BQ40Z50-R1 itself, but what if the BQ40Z50-R1 is getting damaged and there is an internal short between VBAT to GND (see picture below)?

As you can see in the picture above, the current can flow through D1 and BQ40Z50-R1, and short the battery cells. It does not comply with the IEC62368:

How do you recommend to solve this issue?

Do you have any recommendation for a proper battery design?

over 6 years ago

0 Batt over 6 years ago

TI__Mastermind 42535 points

We believe that you are more likely to have an open fail rather than a short. However, I'll confirm this with the design engineers and reply back here.

0 Ravid BY over 6 years ago in reply to Batt

Intellectual 330 points

Thanks for your comment :)

This issue is very urgent to us..

0 Batt over 6 years ago in reply to Ravid BY

TI__Mastermind 42535 points

Ravid,

This is exactly what is protected against by the secondary protector circuit using the bq29610. GND and BAT can never get shorted if your secondary protector works.

0 Ravid BY over 6 years ago in reply to Batt

Intellectual 330 points

Hi Batt,

I still don't understand how the secondary level protection is comply with the sentence marked in yellow.

It says that "a component failure simulated by short-circuiting any two leads and open-circuiting any one lead of the component one at a time;".

This simulation is also considered as single fault condition.

Is it correct?

0 Batt over 6 years ago in reply to Ravid BY

TI__Mastermind 42535 points

Hi Ravid,

Assume you short BAT and GND. Now, the second level protector is going to be driven high at the output and this is going to blow the chem fuse disconnecting them.

0 Ravid BY over 6 years ago in reply to Batt

Intellectual 330 points

Hi Batt,

I agree that if BAT and GND will be shorted then it will blow the chem fuse, but the fuse is located after the cell connection the the BMS (as marked at my first message).

Please look again at the EVM schematics.

0 Batt over 6 years ago in reply to Ravid BY

TI__Mastermind 42535 points

Hi Ravid,

If you have a short at the cell, the gauge can't do anything about it except disconnect the system. The gauge through itself won't allow a short with a second level protector. This is how it has been designed.

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BQ40Z50-R1: Battery safety certification issue