TIDA-00792: BQ76930, BQ78350 and BQ76200 8S BMS Design Short Circuit Problem

Hi Hasan,

Do you mean shorting PACK+ and PACK-? BATT+ and BATT- are not meant to be shorted at any point.

Regards,

Max Verboncoeur

Hi Maxwell, 

I meant to be shorted Pack+ and Pack-. 

Regards,

Hi Hasan,

Could you observe the voltage at the VC5x and BAT pins of the device? Are you using real cells?

It sounds like what could be happening is that the short circuit is pulling the battery voltage down to the point that the device loses power and resets.

Regards,

Max Verboncoeur

Hİ Maxwell, 

Yes we are using the real cells. we observed the voltage drop how can we prevent this ? do you have any recommendations? 

Regards, 

Hasan BİLİR

Hi Hasan,

Referring to TIDA-00792's schematic. D22, D23, and D24 are meant to prevent the supply pins from being pulled down by the short circuit. Do you have these on your design and are they the correct rating?

Ideally when the short circuit occurs, these diodes allow the device to stay powered long enough to trigger the protection and the battery voltage will recover after the FETs are turned off.

Regards,

Max Verboncoeur

Hi Maxwell, 

I compared with the theTIDA-00792's schematic with our schematic.we use the same diodes for D22, D23 and D24. dou you want to check our schematic ? 

Regards, 

Hasan BİLİR 

Hi Hasan,

You could send the schematic for me to check.

Is the device triggering the SCD protection correctly? It is supposed to turn the FETs off before the device loses power. If the FETs aren't being turned off correctly then the device will lose power eventually.

Regards,

Max Verboncoeur

Hİ Max, 

here is schematic link "https://drive.google.com/file/d/1VMJ7oWCZEelSQdDFXXfA6gS6UkCVghI2/view?usp=drive_link" , The  device sometimes couldn't trigger SCD protection and losses power. 

Regards, 

Hasan BİLİR

Hi Hasan,

We're not able to open Google Drive links, or most other file sharing services for security purposes. You can directly upload the schematic to E2E as a pdf for me to look over.

If SCD is failing to trigger sometimes, you may want to observe the voltage between the SRP and SRN pins to make sure that the device is reading the SCD correctly. You may also want to consider changing your threshold or delay settings in the case that they are not properly set for your system.

Regards,

Max Verboncoeur

Hİ Maxwell, 

Is sent you a private message on E2E. also here is my GG file.1_DENEME.gg.csv

Hello Hasan,

Max is out during this week. So responses may be delayed. If you want, you could send me the schematic/info on a private message as well and I can review things. But responses may be delayed somewhat.

Best Regards,

Luis Hernandez Salomon

Hi Luis, 

i sent you a private message on E2E, Please could you review schematic. we couldn't find any reason. also our mosfets burn. 

Best Regards, 

Hasan BİLİR

Hello Hasan,

Do you have waveforms of the VC5x and BAT pins? How much do they drop in voltage?

Usually the D9/D10 diodes would be enough to ensure the voltage on the pins are stable while the protections are being triggered.

I did not really notice anything wrong on the schematic at first glance.

What are the voltages of DSG/CHG during the short-circuit test?

Best Regards,

Luis Hernandez Salomon

Hi Luis, 

we saw the value zero on the VC5x and Bat Pins. also we cannot measure the DSG/CHG pins during the short circuit. 

Best Regards, 

Hasan BİLİR

Hello Hasan,

I understand. Yeah, we have to understand what could be pulling these pins down. Do you have any waveforms of these two pins with respect to the short-circuit?

You could increasing the capacitance on the BAT pin, for example make it 10-uF and see if there's an improvement there.

Looking a bit deeper into the schematic, I do see a point where it is possible that VC5x could be pulled down. I see VC5x connects to Cell 4 through R112, this could potentially bring VC5x down. So you could try removing this resistor or increasing its resistance and see if there's an improvement during the short-circuit

Best Regards,

Luis Hernandez Salomon