Questions on BQ40Z50 based on Application Schematic

John,
The datasheet was updated in December and a lot of information from the bq40z50 Design Guide was incorporated. This information will answer some of your questions.

1) The temperature sensor interface was designed to support NTC thermistors that are typically 10 kohm.
2) The SYSPRES input can be connected to VSS directly or through a resistor.
3) Addressed in the datasheet.
4) These are spark gaps for ESD protection.
5) Provide contact information and we can connect you with Dexerials.
6) The sense resistor must be sized to keep the voltage across the current sense interface less than +/- 100mV. I would use a 1 mohm sense resistor. Note that the device supports up to 32A current measurement range, so you will have to scale the current to support 60A.
7) I have not worked with the Bluetooth devices. The bq40z50 does not provide an external voltage source.
8) Yes, exit conditions are shown on page 41 in the TRM.
9) The SMBus pull-ups must be supplied externally.

Tom

Tom,

Thanks for the quick response. The customer (and myself) really appreciated the feedback. They came back with a couple of additional questions that I hope you can help with.

1. Regarding the current sense resistor, we would like to have the option of measuring and responding to an overcurrent condition, which may be greater than 32A in some applications. That being the case, we would like to consider using a 0.5mohm shunt, unless TI sees an issue with it. We would expect that to give us a +/- 64A measurement range.

 2. We would like our battery cell team to plan for and start the characterization activity that will provide us the necessary data for optimizing the performance of the bq40z50.  What information or tools can TI suggest for undertaking this effort? From their experience with other customers, how long does that effort usually take? As you can imagine, our cell team have necessary equipment for proper testing of battery characteristics.

 3. We would like to consider using the TI technology on battery systems with 8 cells. Which device(s) do they recommend which will allow us to use the same or similar registers (with Z coefficients)?

Thanks,

John

John,
1. Reducing the value of the sense resistor just reduces the voltage between the SRN and SRP pins. The current register can only support and report +/- 32A. The current will have to be scaled to support more than 32A.

2. You can collect current, voltage and temperature data and we can use a Mathcad program to try to find a ChemID match. I attached a document to help in collecting the data. If we cannot find an acceptable match, then we will need to characterize the cell at TI and that is about a 6 week effort.

3. The only Impedance Track device that we offer that can support 8 cells if the bq34z100. It is just the gauge. We also have the bq78350, but it is a CEDV gauge.

Tom

Tom,

In regards to your above comments (1.), how do we appropriately scale when using a different sense resistor? What values must we change? Does performing voltage, current and temperature calibrations using BQStudio account for the changed sense resistor?

On the ChemID response (2.) could you attach the document on data collection? (I couldn't find it). Where can we get the appropriate Mathcad program to characterize the cells? What is the cost of having the characterization performed by TI?

Thanks,

Peter

1122.Chemistry selection.pdf

Peter

The gauge will CC Gain and Capacity Gain for the new sense resistor. Let me know what value you plan to use and I can check to see whether other parameters will need to be changed. I attached the document to help with collecting the data for the ChemID analysis. You can send the log file to me and I can check it for you. Please provide an email address and I will send information to submit a cell for characterization.

Tom

Tom,

We are trying to make a battery of around 35Ah, able to handle currents of 30A continuous and spikes to 60A. We are needing to double the measurable range, so I was planning on using a sense resistor of 0.5mOhm.
I've had a look through that document, but the link to the Mathcad program was broken. I ended up finding a Mathcad Chemistry Selection Tool (dated 16/2/15) under tools and software for the BQ20z90. Where can I download the zip of latest list of chemistries to show up in BQStudio?
Another question on chemistry matching, are we limited only to chemistry files with matching capacity? I looked through BQStudio but didn't find any files of 35Ah with the correct chemistry.
Email me on psvensdotter@daronmont.com.au with any information about cell characterization.

Peter