BQ25750EVM: 10-S Battery issues

Hello Brant,

Thanks for being patient with this.

I have a suggestion for a test to help us debug this. If you plug in the battery by itself and then VAC, can you charge the battery then?

For the boards that are not working, are the BATFETs/ACFETS still in good condition? Can you measure the resistance of R22 and R25 to see if those resistors are good?

Best Regards,
Ethan Galloway

I am hesitant to plug the battery into my one remaining board. R22 and R25 are bad on both boards, reading 1.3kΩ for R25 and about 600kΩ for R22. I replaced them both with new 10Ω resistors. I connected J1 to a 32V PSU so I could read the registers. I was still not getting a Power Good signal so VSYS is disabled. I then turned off the PSU and plugged a battery in by itself then VAC. It did not work and once again R22 and R25 are reading several kΩ. 

As an additional note: every time I plug the battery in (even on a brand new board) I get a pretty good spark so it is like there is a brief short.

Hello Brant,

Thanks for being patient with this. We are very busy right now and I'll get back to you later this week.

Best Regards,
Ethan Galloway

Hello Brant,

We are still debugging this. I have a question for this though .Can you take a look at FETs Q1-Q4 and tell me what FETs are on the EVM?

By the way, I think the spark you are seeing is from inrush current charging the capacitors.

Best Regards,
Ethan Galloway

According to the schematics SIR880BDP. On the Eval boards I have the numbers I see on the actual FETs do not bring up anything on search but they are "66920" and "GV2F23"

I did confirm that the evaluation module will operate from and charge an 8s LiPo battery pack. So the higher voltage from the 10s battery pack seems to be what is killing the eval boards even though 42V should be well within the ratings.

Hello Brant,

Thanks for being patient with this. I'm investigating this and I'll get back to you next week.

Also, do the FETs Q1-Q4 on the board broken board look good under a diode test? You can use the diode test feature on a multimeter to check the FETs.

Best Regards,
Ethan Galloway

Q1- Q4 are all good on both dead boards. Q7 and Q8 are broken on both boards. There is a short between the Gate and Source.

Hello Brant,

Thanks for measuring that. That probably means that a current surge destroyed the BATFETs. Also, if R22 and R25 are damaged on the EVM, that also means the IC is probably damaged as well.

Thanks for being patient with this. I'll get back to you on this later this week.

Best Regards,
Ethan Galloway

Good Morning Ethan,

So I just did a few more tests. I used an inrush limiter (MS35 5R025) and PSU on J3 in place of the battery. At 32V 5A and then 36V 5A on J3 the VSYS (J2) was outputting to the RIGOL DL3021 perfectly. As soon as I increased to 40V 5A the VSYS (J2) stopped outputting anything and will not turn back on. R22 and R25 are now damaged but the BATFETs are still good (the gate to source voltage never exceeded 9V).

This was my third and final eval board (of which I hope you can send replacements once this gets fixed). I hope this information was helpful.

Hello Brant,

Thanks for doing these tests. I'm sorry so many boards broke for this. I'm looking into this and I'll get back to you later on this week. Thanks for being patient with this. I am swamped at the moment.

Best Regards,
Ethan Galloway

Hello Brant,

I have a few questions about this. For your test, did you change the ACUV/ACOV resistors? What voltage did you set the "battery" on J3 too? Also, the RIGOL DL3021 was set to constant voltage mode right?

I'm still working on this I'll look into the replacements and get back to you next week.

Best Regards,
Ethan Galloway

On the first 2 boards I did set ACUV/ACOV but as it did not save the eval board I left them alone on the final test. The voltages I listed on the previous reply where for the J3 "battery". I did both constant current and voltage from the Rigol and it worked great under 36V. When the board died the load was not on. The Eval board just died as soon as I input 40V on J3

Hello Brant,

Can you clarify what you mean by "input 40V on J3"?

I think your board is dying when the charger transitions from fast charge to the constant voltage phase. I wouldn't recommend testing termination or the CV phase with a electronic load.

By the way, when using an electronic load to test, we recommend using a constant voltage supply during the precharge/fast charge phase. If you are testing the termination current, we recommend setting the electronic load to a constant current supply. I also recommend setting EN_TERM=0 during initial testing with an E-Load.

I'll get back to you tomorrow with more information.

Best Regards,
Ethan Galloway

Hi Ethan,

I used a 40V Power supply connected to J3 to simulate a 10S battery pack. I had nothing connected to J1 or J2. As soon as I turn on the power supply the evaluation board ceases to function. 

Hello Brant,

Thanks for the new information. I've never seen an EVM break by connecting a power supply to it. Can you describe how the EVM died?

Best Regards,
Ethan Galloway

It seems we are going in circles here. Could you test plugging in a 10s battery pack on J3 and verify that it is possible? If you can get it to work please tell me how.

Hello Brant,

Sorry for the miscommunication there. I have plugged in 40V to VBAT and I think I'm seeing the same problem that you are seeing.

Let me spend some time investigating this and I'll get back to you later this week.

Thanks for being patient with this.

Best Regards,
Ethan Galloway

Hello Brant,

We are still working on this issue. I will try to get back to you next week.

Best Regards,
Ethan Galloway

Hi Ethan,

Any update on this?

Hello Brant,

Thank you for being patient with this. I'm currently diagnosing the root cause on the EVM right now. I hope to update you on the root cause and the solution soon.

If you want to continue testing the EVM, I would recommend using a CV load instead of a battery.

Best Regards,
Ethan Galloway