Unexpected VC_OV Events Below Threshold during Application Timed Measurement

[MarkFan]

Hi,

I'm using the Application Timed Measurement mode with a sample rate of 24, and have set the over-voltage (OV) threshold at 4250 mV.

However, during charging when the battery reaches around 80% SoC (approximately 4077 mV), some cells occasionally trigger VC_OV events. After manual measurement, the actual cell voltages do not exceed the OV threshold.

What could cause this kind of behavior, where VC_OV events occur even though the measured voltage is clearly below the threshold?

Thanks for any help.

Mark

[MarkFan]

Hi Jozef,

   Thank you for your response.

   Apologies for not providing sufficient information earlier. 

   we using MC33774ATP1AE. and here is the part Schematic.

   Thanks for any help.

best regards,

Mark

[JozefKozon · Accepted solution]

Hi Mark,

thank you for the part number and the schematic. However in the schematic I don't see if you have used recommended components between the Cells and CTx CBx pins. For these recommended components please refer to the section 11.1.1.2 in the MC33774A full datasheet. 

JozefKozon_0-1752661083762.png

Please download the MC33774A full datasheet from the MC33774A product page, under the Secure section. 

JozefKozon_1-1752661287104.png

During fast charging, voltage transients can occur that briefly exceed the OV threshold. These spikes may not be captured by manual measurements but can be detected by the MC33774A. Please measure the voltages to individual cells triggering the OV with an oscilloscope, to check if there are any transient voltages.

Please make sure, that balancing is not on during charging/measurement. During balancing the measured voltage is not guaranteed. 

With Best Regards,

Jozef

[MarkFan]

Hi Jozef,

Thank you very much for your continued support.

The hardware design has already been reviewed and confirmed by our local FAE. Since the MC33774A is already fully integrated into the battery module, we are unfortunately not able to directly probe the individual cell voltages with an oscilloscope.

We also suspected that insufficient control of the charging current might be causing transient spikes, which in turn lead to sporadic over-voltage (OV) events. Your professional explanation has further confirmed our assumption that these events are likely caused by transient behavior.

As a follow-up, we would like to ask:
Are there any software-based methods you would recommend to help identify OV events caused specifically by transient spikes?

Thank you again for your valuable assistance.

best regards,
Mark

[JozefKozon]

Hi Mark,

please download MC33774A safety manual and please refer to the sections 10., 11. in it. There is a description of FTME (Fault Tolerant Measurement Error) for such cases as yours.

JozefKozon_0-1752726524781.png

Please download the safety manual from the MC33774A product page, under the Secure section.

JozefKozon_1-1752726656099.png

With Best Regards,

Jozef

[JozefKozon]

Hi Mark,

please share the full part number of the component you are using.

Please share your schematic with voltage levels and part values.

With Best Regards,

Jozef