BQ76930: Sampling accuracy change.

Hi User,

1. This is unusual, at room temp 25C the error is typically within 10 mV as shown on the data sheet.  Assembly stress is known to be able to cause shift of one or both cell groups.  Reflow of the solder without board stress has normally fixed this.

2. Again 15 mV is a little large, what did you do to reduce the error from (1)?

3. Drift of the part with a large magnitude is not expected.  

Suggestions: Check the voltage across the input filter resistors to see if there is current going into the VCn and power nodes.  When the part is in shutdown these are quieter, with the part operating they can be more jumpy as the part samples cells and thermistors.  Currents are small as shown in the data sheet so the voltage readings should be small.  If you see a sizable value it could be leakage current into the capacitor, the board, contamination or board coatings, or the IC.  With a positive voltage on one VCn and a negative on the next, look for leakage of the related capacitor or something between the pins.  The IC could be damaged but it seems unusual to drift with time. Customers have experienced both board and capacitor leakages which varied with time. You might try warming the board to drive off any moisture.  Separating leakage of the board, cap and IC can be difficult since heating to unsolder the IC heats all 3.  You might be able to remove a capacitor with hot tweezers without significantly heating other components or areas.  In some cases you may need to manually cut the traces or IC pins to isolate the source, it is obviously destructive testing.  

Please let us know what you find.

Dear WM5295

       You said it is  board stress,but I had take the device away from the board, then solder the device on the board again, but the phenomenon is the same. I had try five unusual boards, the phenomenon are same, can not be resolved.

       So I don't think it because board stess.

Hi User,

I agree, if you have reflowed or reworked the part I would expect the board has taken its shape from the initial processing and the part should now be free from board stress unless it is bent by installation in a housing.  I doubt you have that since you are working to understand the cause. 

Have you tried to put the part from an unusual board onto a good board and does the problem follow the part or the board? 

Dear WM5295

     I had tried to put the part from an unusual board onto a good board, the problem follow the device, not board, I had tried three devices, are all the same.

Hi User,

That does seem odd.  If I understand, the part would have the large error on board 1, recover when heated, be heated twice for removal from board 1 & installation on board 2. On board 2 it shows a large error, when heated the error would decrease.

Please see the customer return process http://www.ti.com/support-quality/additional-information/customer-returns.html If submitting a return be sure to include good details of the problem encountered, processes, times, voltages or other relevant information.

Shipping typically takes a few days, so if it is an issue which occurred over time it may show up when tested although shipping is not a controlled temperature.  If it must be biased for some days for the error to show up that is an important detail to include.

Dear  sir,

would you please  comment how to deal with these return IC  for your double check?  you address/name?

Also you can send a mail to  jack-li@ti.com for your information.

Regards,

Jack

Hi Jack,

Please follow the instructions in the customer returns page http://www.ti.com/support-quality/additional-information/customer-returns.html 

To summarize: If you purchased from a distributor please contact the distributor and work with them for the return.  If you purchased directly from TI please fill out the page linked from the customer returns page.

Dear WM5295

      I had submitted customer returns, CPR201036183

      But I don't know send to who, Please give me your consignee information, Thanks a lot.

Dear WM5295      

       I had submitted the customer returns, CPR201036183        

       Please give me your consignee information.

Hi User,

You should have some communication back from that system which gave you the CPR number.  If you ordered directly from TI be sure to enter your sales order information.  If you ordered through a distributor please contact the distributor.

Please work with the contacts in customer return system.  E2E is for technical support rather than returns.