BQ40Z50-R2: Charge Provided to the battery / Total time that battery in fast charge mode.

Hi Chandan,

No, that's not how it works. You are going to charge in CC/CV mode which means as the voltage of the cell increases, the current will start to taper off from it's nominal charging value. This is how we detect charge termination. In a bad battery with a high resistance, or with an old cell the cell terminal voltage will rise faster due to the higher resistance seen, this means your current will start tapering off early. So you can't use charging time to determine if a cell has gone bad. One way to check it is to use the state of health. Another way to determine aging is to use the Ra table. Compare how Ra4 changes. If your MCU can store the golden value from a learned new pack and use that ratio between old and new values, or compare SOH FCC against Design Capacity.

Hi Batt,

Thanks for your response.

You are right about detecting the charger termination/ full charge. We are following the same (as per TRM).

Sorry may be I was not clear. 

My Understanding:

1. Pre-charge time out error (PTO): If a battery pack / cells stays more than PTO time in precharge state (PV=1). FG detects it as fault condition and stops charging.

2. Similarly, fast charge timeout error (CTO): If battery pack is in charging mode for than CTO time, fuel gauge detects as fault and stops charging.

This timeout error is also followed in standalone battery charger ICs also. The timeout condition is detected as fault condition and stops charging.

Can you please help me to understand what is the purpose of these features ? If not a bad battery condition what fault condition are we expecting ?

If you have any application note on these please share.

Thanks,

Chandan N

1. You are right about that.

2. You are right about that as well.

The reason we have timeouts is because you cannot perpetually keep charging the battery without the terminal voltage of the battery rising. If it doesn't rise, it means either the battery has gone bad or there is something wrong with the system. For this, we use our knowledge about the rate of charge and the capacity of the battery to detemine a suitable level at which you acn declare a timeout.

We don't have app notes for these features.

If you have any questions, please post them, I'll answer them here.

Hi Batt,

Understanding:

As you mentioned to avoid keep charging the bad battery, when it is not reaching valid charge termination condition within the expected time, we can use timeout feature. This timeout delay can change based on the rate of charging current (simply charging current value). So this timeout delay represent the total charge provided to the battery during that time.

Please correct me if am wrong.

Query:

As I have mentioned in my first query, we will change the charging current based on the system load condition. Charging current can be 1A or 128mA. This is to ensure that overall system load is within the ac-dc converter specification.

If CTO delay is set to 4 Hours (example for a 3000 mAh battery) by keeping in mind the charging current of 1A, 4 hours may not represent the correct charging time for lower charging current.

So we have 2 option,

1. Keep more (as compared to 4 hours)  CTO delay to accommodate the total charging time required for lower (128 mA) charging current.

Is it okay to have higher CTO delay while charging at 1A? 

OR

2. Dynamically change the CTO delay as and when we change the charging current.

We would like to avoid this dynamic programming of the CTO by MCU, as CTO is a safety parameter.  

Is there any other way to check the total charge provided to the battery ? Instead of time, we can look into the charge data and we can stop charging?

Accumulated Charge measurement feature is present in BQ40Z50-R3.

Is there a similar method to extract the total provided charge data in BQ40Z50-R2?

Thanks,

Chandan N

Hi Batt,

Thanks for your support.

I will go through the Qmax passed charge and DOD0 passed charge parameters.

Will come back to you for queries.

Thanks,

Chandan N