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bq27510-g2 recommended settings

Piotr65441
Prodigy 120 points
Other Parts Discussed in Thread: BQ27510, BQEVSW, BQ27510-G2

Hi,

I've started to experiment with a newly added bq27510-g2 to our design. I'm using EV2300 and communicating with the target board. So far, so good. One minor thing, though - where can I find or how do I generate bq27510_1_23.dfi file with defaults for my gauge? This file is not included with the bqEVSW package. There is one, but for older firmware (1.21)? I would like to have this file so that I can always reset everything to defaults...

Now let me jump to the main questions regarding the recommended settings. Our design uses 6800 mAh battery. The standby current is ~5mA (GSM modem), the off current is around 0.5mA and when in active mode it uses avg 30-40mA and something around 100-200mA (average) when communicating with some current peaks usual for GSM. I'm using 10mohm sense resistor. The charger passes up to 2A current.

1. Should I leave deadband set to 5mA as this seems to be default? Does that mean that I might see the average current as 0 when it stays at lower values, for example 3-4mA? I don't have to monitor the current values but was wondering if lowering deadband value is a good thing to do?

2. How should I decide whether to use "FC Set %" with value -1 or something between 90-100%? Any advantages, disadvantages of each type of termination detection?

3. Now the hard part. What values shall I use for "Dsg Current Threshold" and "Quit Current"? The defaults (60mA and 40mA respectively) seem to be too high. Are they? Won't bq27510-g2 consider the battery to be relaxed instead of discharging most of the time, when there actually is some current consumption (and I consider the device to be in active mode), for example 30-40mA? Or is it OK to let bq27510-g2 think the battery is relaxed and with this 6800mAh battery I should even make these values higher (closer to C/20)?

I consider  "Chg Current Threshold" (75mA) to be OK for my design.

4. Shall I lower the Initial Standby Current to 5mA? Will it make any difference?

5. Can I somehow divide the learning cycle (discharge, charge, discharge) into parts? I now that discharge and charge have to be continous. But can I turn the device off (along with bq27510) and close bqEasy, for example, after charging to continue later with the final discharging?

Also, can I do the first discharge outside of the device with bq27510 and then connect everything back and just start charging?

  • 0
    TI__Intellectual 2100 points

    Piotr,

    I apologize that the default DFI was not included.  We'll get the release fixed as soon as we can.  In the meantime, here is the default DFI for the G2 firmware.

    http://e2e.ti.com/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/180/6428.bq27510_5F00_1_5F00_23.dfi

    As for your questions:

    In general, we recommend using the bqEASY wizard to go through this process, as it will ask questions and change the critical values for you to reflect your system parameters based on your responses.

    1) We generally recommend not changing the deadband.  It has additional functionality that allows us to calculate accumulated error by the coulomb counter.  The default value in this case is based on what we empirically observe to be the best value.

    2) The FC bit is a flag and does not intrinsically affect the behavior of the algorithm.  This value determines how this bit behaves and reports information to you.  If you plan on using the FC bit to trigger certain events in your system (for example, if you have set the BAT_GD pin function codes to disable the charger upon assertion of FC), then this value will determine at which measured State of Charge the FC bit will be set.  Otherwise, if you are not using FC then this setting is a 'don't care'

    3) This parameter is generally set in bqEASY based on your estimated discharge currents.  The Defaults of 40 and 60 will need to be tweaked.  Generally, you want these currents to be hysteretically distributed and less than your minimum discharge current in active mode (not in standby/off).  Also note that for battery discharge, what is important for relaxation is the C-rate as you mentioned.  In practice, generally consider current less than C/10 to be acceptable 'relaxed' currents, as the voltage drop across the internal battery impedance is basically negligible for these currents.  Therefore, for your 6800mAH battery, a current of 30-40mA is very small, and the battery would effectively be 'relaxing' during this time period.  As a result, having a threshold of 75mA is just fine.

    4) The gauge will learn the standby current of your system, but the initial standby current is just a first guess.  It won't make much of a difference as long as the guess is reasonable.

    5) We generally don't recommend resetting the gauge during the relaxation periods, as the gauge must obtain a good voltage measurement after the charge and just before the discharge.  If you know how to time it such that both measurements happen and are successful, I believe that it is possible, but we do not recommend it.

    Let me know if this helps,

    Charles

     

  • 0 in reply to Charles Herder
    Prodigy 120 points

    Charles,

    Thanks for the DFI file and the answers. 

    I am still not sure about the Dsg Current Threshold and Quit Current. As I stated earlier, my lowest possible active current is about 40 mA, whereas the standby current is about 5mA. You stated at the end: "As a result, having a threshold of 75mA is just fine". But won't having this threshold as high as 75mA cause any problems? For example, I imagine that Average Current will be zeroed every time the bq27510 considers the battery as relaxed, won't it? It isn't a big deal for me, but if possible, I would like to be able to monitor my average active mode current.

    What about setting Dsg Current Threshold to 25mA and Quit Current to 15mA? Are these values too small? Also, should I treat the value in Dsg Current Threshold as an average or temporal value?

  • 0 in reply to Piotr65441
    Prodigy 120 points

    I will just answer myself. These settings are set automatically by bqEASY, so I think I can trust it. Somehow I haven't noticed this eearlier, or somehow bqEASY didn't write these settings to Flash.