BQ35100: Operation Mode Suggestion for Frequent Capacity Measurement

Hi,

Can you not leave the device on the entire time? 

How many times do you expect to call a gauge stop cmd in 1 battery discharge?

Regards,

Evan

Can you not leave the device on the entire time? 

Unfortunately no. The above behavior is a simplification of the system, by default the device will sleep most of the time but depends on some external trigger it could wake up every 2 minutes for it's entire lifetime.

How many times do you expect to call a gauge stop cmd in 1 battery discharge?

It only calls gauge stop 1 time every sleep cycle. So, that means gauge stop will be called every 2 mins

Hi,

Sorry for the confusion I meant is it possible to leave the gauge on the entire time?

Ok so the device flash is rated for 200,000 writes, every 2 minutes is 720 writes a day, meaning the device flash will wear out in about 277 days. Do you expect the non-rechargeable battery life to exceed 277 days? 

Is it necessary to send a gauge start/stop cmd every 2 minutes?

Also, when GE is low the device is not active.

Regards,

Evan

Sorry for the confusion I meant is it possible to leave the gauge on the entire time?

Unfortunately no, leaving it on the entire time will significantly reduce the battery-life

 Do you expect the non-rechargeable battery life to exceed 277 days? 

Yes. Also, based on this thread it seems the flash is rated 20,000 writes

Is it necessary to send a gauge start/stop cmd every 2 minutes?

I only want to measure the used capacity at high-power pulse which could happens every 2 minute. and If I understand it correctly I need to do gauge start before the pulse, and gauge stop after the pulse to get the measurement.

Hi,

Yes this is correct.

Regards,

Evan

Going back to my question, Can I disable flash update when I call GaugeStop()?

Hi,

Unfortunately, there is no way to disable flash updates when a cmd GaugeStop() is called.

Regards,

Evan

I see, since I only interested in the used capacity between wake-up, do I need to care about flash wearing-out? What's the behavior of the AccumulatedCapacity() when the flash wears out?

Hi,

If you wear out the data flash, you will not be able to write values to data flash.

I have never tested a device with DFW but I would assume AccumulatedCapacity() will be incorrect since the accumulated capacity is loaded from DF.

Regards,

Evan

Got it thanks for the info!
Last question from me, can I set GE to low and NOT call GaugeStop(), so that it will not write to flash? Will this cause other issues?

Hi,

No problem!

I have never seen this before, but I would think if you don't update the value in flash with a gaugestop() cmd then it will continue to use the previous saved value which would be incorrect.

Thanks,

Evan

Ohh I see, so if I understand you correctly the AccumulatedCapacity() will not be updated if we do not call GaugeStop()?

Hello,

Today's a national holiday. We will get back to you tomorrow.

Regards,

TI Apps Team

Hi Aldwin,

You are correct.

Regards,

Evan

Diego said:

I have never tested a device with DFW but I would assume AccumulatedCapacity() will be incorrect since the accumulated capacity is loaded from DF.

Let's say the DF wears-out and I managed my capacity counting externally ( for example in the cloud )

Technically, if i do the following:

1. Send GaugeStart() 
2. Read AccumulatedCapacity() ----> save this externally as capacity-at-start.
3. Start and stop high-power process
4. Read AccumulatedCapacity() ----> save this externally as capacity-at-stop.
5. Send GaugeStop()

I should still be able to calculate the used capacity at that high-power process moment, by calculating the delta between capacity at stop and start right?

Hello Aldwin, 

I do not believe this work around will work, because at this point the AccumulatedCapacity() will not get updated since the DF is worn out. I would recommend to have less frequent writes to prevent a premature DF wear out. 

Regards, 

Jonny. 

based on the SLUUBH1CTRM Section 5.1.1,

Sending the GAUGE_STOP() command prior to the GE pin being pulled low initiates the latest value of AccumulatedCapacity() to be written to data flash memory.

If I understand it correctly, AccumulatedCapacity() is incremented in-memory and only gets written to DF when GaugeStop() is called.

So, in step 4 since it hasn't been called yet there's no interaction with the DF, and I should be able to get the updated AccumulatedCapacity(). Is that correct?

Best,
Aldwin

Hi Aldwin,

Let's assume the number for accumulate capacity is 100.

When a gauge start cmd is sent it will load the value stored in df for accumulated capacity (100).

Then it will add to this value until a gauge stop cmd is sent. You can track how much is added using the accumulatedcapacity() cmd.

Once the gauge stop cmd is sent the gauge will write the new accumulated capacity into data flash. (for this example, 110 is the new value)

Let's assume that was the last write and the data flash is now worn out with an accumulated capacity number in df of 110.

From this point forward every time you send a gauge start cmd 110 will be loaded and every time a gauge stop cmd is sent the value stored in df will not update.

If you have any more doubt about how this function works I suggest purchasing an EVM and testing a work around solution for your product.

BQ35100EVM-795 Evaluation board | TI.com

Regards,

Evan

Diego said:

Then it will add to this value until a gauge stop cmd is sent. You can track how much is added using the accumulatedcapacity() cmd.

and I can call AccumulatedCapacity() cmd before sending gauge stop, right? This is what I observe in the BQStudio.

Diego said:

If you have any more doubt about how this function works I suggest purchasing an EVM and testing a work around solution for your product.

BQ35100EVM-795 Evaluation board | TI.com

Yes, I have this board and I'm able to connect to the BQStudio software.

Hi,

Yes, this value will not be written to flash until the stop cmd.

Awesome!

Regards,

Evan

Got it!

So this means, even though the flash wears-out, I can still track the current used capacity by calling AccumulatedCapacity() before gauge stop, and I can save it externally ( for example the cloud ), right?