• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 871 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ20Z95 EMI (Radiated Susceptibility EN55024 and EN55022) Issues with AFE, Request for all EMI Suggestions

jonathan digiacomandrea
Prodigy 190 points

Community,

 

I have a newly designed battery pack (4S2P 18650 3.0-4.2V cells) with an integrated charger. This pack has recently undergone testing to the EN55024 and EN55022 standards and has failed while in charge mode. The issue is that the pack apparently "shutdown" while in charge mode as soon as the test house applied a 3V/m ~80Mhz signal to the chamber. As the test house was not able to send the entire pack back I had them send the PCBA back and I have done a preliminary failure analysis. I have found that the pack went into a permanent failure mode with this written to the "PF Flags 1" field: 0100. This seems to translate to a AFE_C error. I also have some seriously wacky measurements for cell voltages, temperatures etc. It looks to me that some RF got on the cell voltage lines (the low pass filters are too far away from the IC, this is being corrected) Also the Thermistor is on a wire harness, with little to no filtering, this is also being corrected. The real question is why did a communication error arise? Is this a problem on the Die of the IC?

 

If anyone has any experience with EMI susceptibility and the BQ20Z95 I am all ears. I am inexperienced in EMI design, throw all suggestions my way please!

[Device Status Data(PF Status)]

PF Flags 1 = 0100

Fuse Flag = 00

PF Voltage = 25080

PF C4 Voltage = 6338

PF C3 Voltage = 6252

PF C2 Voltage = 6221

PF C1 Voltage = 6270

PF Current = 891

PF Temperature = 400.1

PF Batt Stat = 5890

PF RC-mAh = 65

PF RC-10mWh = 790

PF Chg Status = 0048

PF Safety Status = 4140

PF Flags 2 = 0100

[AFE Regs(PF Status)]

AFE Status = 00

AFE Output = 08

AFE State = 00

AFE Function = 00

AFE Cell Select = 00

AFE OLV = 12

AFE OLT = 0F

AFE SCC = 00

AFE SCD = 77

Thanks so much, E2E is great.

JD

  • 0
    TI__Expert 6470 points

    Johnathan,

    Sorry about your experience. Once you determine the root cause, or find a good fix it would great if you could share it here. I agree with your approach, but would add the following things to consider:

    1. AFE_C means the gauge was having alot of trouble communicating with the AFE die inside the package. Those I2C and other connections are super short, so its very unlikely that they could have any susceptibility to a wave as long as 80 Mhz.

    2. Sometimes AFE_C can be caused by excessive resets. You can query the number of resets that the gauge experienced using a special command as mentioned in the Tech. Ref. Manual. If they are excessive, then the cause of the resets should be determined and fixed. As you probably know, any semiconductor junction can rectify RF, and then you have a DC current to deal with which when strong enough can cause all kinds of issues. If resets are occuring, you can use them as a debug tool to try to figure out which pin is the source of the noise. For example, lift each pin that can be lifted and look for improvement. Pins that can't be lifted can be shunted to IC ground with a 100 pf cap with very short leads. Also, insure that the reset trace between pins 30 and 35 is not excessively long.

    3. Even if resets are not occuring, I think a good general troubleshooting procedure is lifting pins and shunting to ground with a small cap while applying the stimulus that causes the failure. Once the offending pin is found, you can look at shielding the trace with ground underneath it and on both sides, making it shorter, or both.

    4. Since 80 Mhz produces a relatively long wave of several meters, only the longest traces in your system are likely to be effective antennas. So, again I agree with your approach to suspect the battery connections and thermistor connection.

    5. Insure that the main 2.5V 1uf decoupling cap on pin 32 is close to the IC and returns to pin 31 & 34 with a short trace. 

    Rgds,

    Doug

  • 0 in reply to Doug Williams4811
    Prodigy 190 points

    Doug,

    Thank you so much for your input! I didn't even know about the excessive resets causing a PF. I will be doing some additional troubleshooting this weekend. I will take a good look at the layout with the pins you mentioned. I really appreciate your input, this rf stuff is quite new to me and I am learning very quickly, but there is so much to it!

     

    Thanks again and I will surely post what I learn,

    JD

  • 0 in reply to jonathan digiacomandrea
    Prodigy 190 points

    I read the resets and the WD resets, got 0904 from Reset Data and 0001 from WD Resets. AFE Fail limit is set to 10, does this show a error? or is 9 one short?

  • 0 in reply to jonathan digiacomandrea
    Prodigy 190 points

    We have finally concluded testing on this product and passed all EMI/EMC requirements. We have found that decoupling capacitors as close as possible to the Chip are the best help for preventing noise from working its way onto the chip.