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bq27500-v130 with small capacity Li-Ion single-cell batteries?

James Hillman
Expert 1436 points
Other Parts Discussed in Thread: BQ27500-V130, BQ27510-G3, BQ27500

Hi there,

I haven't used a fuel gauge IC before and I was hoping someone could just check that I am not misleading myself - I plan to purchase the EVM to de-risk. 

I am looking at the bq27500-v130 to monitor low capacity single-cell Li-Ion batteries. Capacities range from 1mAh to 200mAh, with currents of 0.5mA to 1mA. The datasheet doesn't indicate any minimum capacities or currents - though I noticed the states rely on currents < or > C/20. I figured, if the models and gold image - it can learn for any type of capacity battery. 

Does this seem correct?

Hopefully it does - this IC would be great for my application to calculate available capacity (at full charge, current state) and also to fact it considers the fact the load system might have more than one current mode - low power mode (150uA) and when its active mode (0.5 to 1mA). Seems like it could provide some excellent confidence - I am excited to test it.

  • 0
    Expert 1436 points

    Hi Gurus,

    Any chance anyone is looking at this for me? I am holding off as I still unsure. I have done some further reading and I wonder if the issue might be more to do with current sensor resistor - I was reading SLUA439 and I think my errors would be fairly large (50%) for 50mOhm resistor. How in Table 4 was the STANDBY Threshold calculated? As long as the voltage doesn't exceed the limit can I use any value i.e. to reduce this error?

    To restate my original questions:

    1) Can I configure the C/20 threshold to a different level? The datasheet says its programmable - which I assume means edit the firmware rather than the flash registers?

    2) Is the setup going to be able to measure standby at 150uA, active between 400uA and 1.5mA?

    Best Regards,

  • 0 in reply to James Hillman
    TI__Expert 4115 points

    Hello James,

    With current levels so low in your application you are going to want to rely on accurate voltage measurements because accurate current measurements are going to be difficult.  We typically consider anything below 5 mA to be in a "deadband" and do not report current below that threshold.  You can try to scale your sense resistor accordingly on an EVM and test out the results.  As long as you fall in teh +/-125 mV range you should be all right. 

    The bq27500 is an old device, I definitely do not recommend that device.  If you are looking for something in a larger QFN package teh bq27510-G3 is where you want to go.  Our most recent system side CSP gauge is the bq2750-G4.  Also, considering your application you might look into the bq2720-G1 which uses new algorithm on IT-DVC (Impedance Track Dynamic Voltage Correlation).  The '620 estimates current based on robust battery model used by the gauge.

    I hope this helps.

  • 0 in reply to Jared Casey
    Expert 1436 points

    Hi Jared,

    Thank you very much for your reply. The '620 looks interesting - does it use the same learning cycle and manufacturing steps as the 27500? i.e. software tool to find the data tables for the models? Calibration during manufacture? Anything new related to the DVC? 

    I found Yandong Zhang's slides on IT-DVC which looks impressive. 
    http://www.batterypoweronline.com/conferences/wp-content/uploads/2013/06/TI_YandongZhang__dynamic_voltage_correlation.pdf

    Also, regarding the  bq27510-G3 do you know where I could find the technical manual rather than the datasheet?

    Also, I wasn't able to find the bq2720-G1 - typo somewhere in the name?

    I'd be grateful for your final reply,

    All the best,

    James

  • 0 in reply to James Hillman
    TI__Expert 4115 points

    Hello James,

    The '620 will have the same flow for the most part as the '520 when it comes to manufacturing.  I believe that you complete 2 learning cycles because the first cycle is for current optimization.  I will need to check on that though.  Yes, the information from Yandong will be most helpful, he is the creator of this algorithm.

    So, big typo on my part...you will want the '520-G4 (NOT '520-G1...sorry! :-/).  The '510-G3 was developed from the '520-G4 so you can check out the TRM from the '520-G4 as we are still in the process of updating the information for the '510-G3.

    I hope this helps.