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BQ34Z100: Golden file example, SOC accuracy and current sense input resistors questions

Part Number: BQ34Z100

My customer has the following questions:

1.      Can you provide us with an example golden file for the BQ34Z? The cell that we will be using is INR18650_F1L (Li-ion) and GP210AAHCB (NiMh), both cell data sheets are attached. Can you please check and confirm if you already have the Chem ID and the golden file for these cells?. If not, what is the process of getting the files?

2.      Does the Gauge require to do a calibration over time to main the SOC accuracy?, does it need host intervention?

3.      In the flags() status register, what action is expected from the host if the condition flag (CF) is set?

 

 

4.      The Rsense that we are currently using is 20mohm, is it OK or do we need to change it for better accuracy?

5.  We have to also consider any intrinsic safety (IS) implications for the design and as such I have the below question.

On pg. 47 of the datasheet, the schematic shows 2 low pass filters , one for each node across the sense resistor. The values are R5, R6=100ohm, C5, C6 = 0.1uF. The cut off frequency is around 16KHz.

 

We will need to increase the resistance from 100ohm to 470ohm for IS requirements and as such to maintain the cut off frequency, have to change the capacitors to 22nF. So the new values will be R5, R6 = 570ohm, C5, C6= 22nF.

 

Do you see any concern with this change, I believe both these nodes should be high impedance and changing resistance from 100ohm to 470ohm should have minimal impact?. Can you please confirm and also pose this question to the factory if this change is OK.

Thanks!

Best Regards, Mark P

  • Hi Mark,

    1. The defaults values in the SREC are for li-ion. These values will need to be modified to suit your application. To find a suitable ChemID match, please use the GPCCHEM tool found here: http://www.ti.com/tool/gpcchem

    The steps for running a chemID match are described in this document: www.ti.com/.../slva725

    2. After the gauge is initially configured, it will self calibrate without host intervention.

    3. If MaxError() exceeds Max Error Limit, then the [CF] bit in ControlStatus() will be set. It will be cleared when MaxError() returns below the value of Max Error Limit. The host does not necessarily need to act, but needs to be aware that the data may not be as accurate as a Qmax update has not occured. Allowing the conditions for the gauge to update Qmax will alleviate this condition (running an update cycle). More information on the conditions required for an OCV reading, please refer the customer to section 8.3.6.8 of the device datasheet.

    4. 20 mOhm is within the range specified in the datasheet. All other parameters being equal, this size current resistor will give better accuracy over a more limited current range than a 10 mOhm sense resistor (default value on the EVM). Please be aware that operation will be limted to 6.25 A with a current sense resistor of this size. Also, perform current calibration to set the value properly in dataflash.

    5. Impact should be minimal, but there is no replacement for empirical testing. Please let me know if any issues arise.

    Sincerely,
    Bryan Kahler

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