BQ40Z50-R1: FUSE BIT SET

Hello Darren,

If you add a 50kOhm path to ground do you still see the fuse blown? The gauge can also detect if there is another external device that has tried to blow the fuse. Can you share your .gg file so we can verify your configuration does have the fuse disabled?

Sincerely,

Wyatt Keller

Pack-3_vs_Pack-5(2).xlsx

The attached file contains a side-by-side comparison between a pack which Passed our Final Test (Column D), and a pack which Failed our Final Test (Column E).  The data in Column E is from the pack with the FUSE bit = 1.  The values that are different are in yellow.

Your help is very much appreciated Wyatt.

Darren.

Re the 50K from the FUSE pin to gnd.; These packs are sealed in plastic.  It would take a while, but I could cut one open if you think it's worth it?

Hello Darren,

Do you know the occurrence rate for this since it sounds like some are passing? If you upload the SREC from a bad gauge to a good gauge, does it follow the gauge or the firmware?

If the FUSE is setting right when you upload the firmware then you can try uploading to an EVM or other prototype board to see if it has the same behavior.

Sincerely,

Wyatt Keller

Wyatt, I was able to swap the srec's and GG files between a working pack and a bad one.  the FUSE bit stayed set in the bad pack, and stayed cleared in the good pack.  So the issue is staying with the gauge.

As far as the occurrence rate; we built 148 packs, 39 of which have this issue.

I will run the test to determine if the fuse bit sets right at programming, asap today.

Thanks Wyatt.

Hello Darren,

Can you also confirm the voltage on the FUSE pin and if there are any other PCB or manufacturing defects that may put a voltage on this pin?

Sincerely,

Wyatt Keller

Hello Darren,

Since this looks like it's following the hardware, I think the best next step would be to do an ABA swap for a good and bad part to see if it's following the actual gauge or the PCB. Once we can confirm this, we may need to try to do some Failure Analysis on the part which we can take offline with your FAE.

Sincerely,

Wyatt Keller

Hello Wyatt, while I have been studying this issue I have noticed that performing a software Reset does not clear the FUSE bit, but doing a Power On reset (i.e. while attaching cells) does clear the FUSE bit. This has resulted in my "bad" sample now being good.  So as far as the ABA swap, I feel like I'd be swapping a working chip (which was bad) with a good chip. I'm happy to do it if you think it will shed some light on what's going on.  Do you still want to do the ABA swap?

Also I have been contact the our sales rep Mr. Tuna he is steering us towards you as the person we might have a quick conference call with.  Is that possible?

Hello Darren,

From previous testing you saw the uploading the SREC from a "bad: device to a "good" device you saw the FUSE bit stay high? But when you power cycle the gauge it goes away?

There is no need to do an ABA swap if a power cycle resolves the issue, if all the firmware configurations to enable the fuse are disabled, then the only other way I can think of is there is some voltage on the FUSE pin making the gauge think a secondary protector has triggered the fuse.

We can work through Jon if necessary to clarify anything further. It looks like the issue may be resolved, are you able to recreate the issue after clearing FUSE with a POR?

Sincerely,

Wyatt Keller

Hello Wyatt, No we are not able to recreate the FUSE issue after it's been cleared with a POR.

However we do have a question re the Reset method.  The staff is asking; what's the difference between a POR and a BQ studio Reset command?

Hello Darren,

Let me check with my team an the exact differences, I will try to get back to you later today.

Sincerely,

Wyatt Keller

Given that the Gauge is not enabled to blow the fuse (see GG file I sent) and the FUSE pin is grounded to VSS of the Gauge, what could cause the FUSE bit to set in the first place?

Understood, thanks Wyatt.

Staff is asking; "is there any way to reset that bit once cells are attached?"  As it happens our process involves attaching the cells via welding to the PCA, so removing and re-attaching is not an option.  Do you know if there is any pin on the Gauge which could trigger a POR?

Wyatt, let me first apologize for basically asking the same question many different ways. I am very sorry about this.  It's been pointed out  that your response indicates there is no way to cause a POR event via the software.  I'm being asked to find out if there is a pin we can short on the Gauge to cause a POR event.   (We think we know the answer, but in an effort to avoid scrapping product, we need to ask).

Again, I appreciate your patience!