BQ27Z561-R2: CHEMID for LTO single cell battery

Marvn Arcangel

Part Number: BQ27Z561-R2
Other Parts Discussed in Thread: GPCCHEM, BQSTUDIO

Hello,

Our customer wanted to use this device with a Lithium Titanate Oxide single-cell battery. They have followed the instructions for capturing a log file using bqStudio and have sent the log file to GPCCHEM website. However, the result of the submission was that a suitable CHEMID could not be found.

Would you kindly help on how to get a suitable CHEMID for this battery?

Please refer to the battery details and log files provided by the customer below:

The nominal voltage of the LTO is 2.4V, the full charge voltage is around 2.8V and the discharged voltage is approximately 2.2V

GPCPackaged (1).zip

Thank you.

Regards,

Marvin A.

over 3 years ago

0 Wyatt Keller over 3 years ago

TI__Guru** 105760 points

Hello Marvin,

Was the gauge being used to collect the data? It looks like this batteries capacity is very small, can you send the battery specification/datasheet?

The discharge current accuracy is not very good and the discharge current itself is very small. There may not be a good chem ID match since this is a less popular cell chemistry.

Sincerely,

Wyatt Keller

0 Sid Price over 3 years ago in reply to Wyatt Keller

Prodigy 245 points

Hello Wyatt, Marvin,

The data was logged using bqStudio and the bq27z561EVM.

The battery capacity is 100mAh and the discharge was chosen by following the guidelines in SLVA725A (C/10).

We do not have a datasheet for this battery. As Marvin noted it has a nominal voltage of 2.4V, charge cut-off of around 2.8V, and a discharge voltage of 2.2V.

I think you are correct in that none of the available Chem IDs are suitable, however, we are hoping a custom Chem ID would enable us to use this device.

Best regards,

Sid

0 Wyatt Keller over 3 years ago in reply to Sid Price

TI__Guru** 105760 points

Hello Sid,

The current accuracy should be a little better, what size sense resistor are you using? Was a calibration completed before testing?

We can do a custom chem ID if needed. I have sent you a friend request.

Sincerely,

Wyatt Keller

0 Sid Price over 3 years ago in reply to Wyatt Keller

Prodigy 245 points

The sense resistor is what is fitted to the eval module. Would need to examine the schematic.

0 Sid Price over 3 years ago in reply to Sid Price

Prodigy 245 points

Hi again, the EVM has a 0.001R sense resistor.

Calibration was not done; I am not sure what that procedure looks like.

Sid

0 Wyatt Keller over 3 years ago in reply to Sid Price

TI__Guru** 105760 points

Hello Sid,

The calibration process is outlined in the EVM users guide. I would also recommend increasing the sense resistor if you are only working with low currents, otherwise the effective resolution you will have will be very low.

Sincerely,

Wyatt Keller

0 Sid Price over 3 years ago in reply to Wyatt Keller

Prodigy 245 points

Hi Wyatt,

Sure, I can increase the sense resistor. What do you recommend? I think the maximum according to the data sheet is 0.010R?

Also, I will look at the calibration procedure.

Once those two things are done, I assume I should run the relax, discharge, relax logging again?

Sid

0 Sid Price over 3 years ago in reply to Sid Price

Prodigy 245 points

Hi Wyatt,

Looking at the datasheet it appears the maximum voltage input on the sense pins is 0.1V I think. We have an expected peak (pulsed) current of 200mA, so if I swap the sense resistor for 0.25R that would yield +/- 0.05V. Does that sound about right?

Sid

0 Wyatt Keller over 3 years ago in reply to Sid Price

TI__Guru** 105760 points

Hello Sid,

Yes after calibration and using a better matching sense resistor the data should be collected again. It still may not be good enough since 100mAh is the minimum this gauge can support.

You don't need to use the full range, it may overflow the calibration values. You can test with a 0.25Ohm sense, if the calibration fails I would recommend decreasing the size.

Sincerely,

Wyatt Keller

0 Sid Price over 3 years ago in reply to Wyatt Keller

Prodigy 245 points

Hello Wyatt,

I have ordered some 0.25R resistors and should be able to test this next week. Should I post the test results here?

Sid

0 Sid Price over 3 years ago in reply to Sid Price

Prodigy 245 points

Hello Wyatt,

I have calibrated the gauge after changing the sense resistor to 0.27R. My quest, before I run the relax, discharge, relax, test again is what load current do you suggest for the discharge cycle? The battery is a 100mAh cell.

Sid

0 Wyatt Keller over 3 years ago in reply to Sid Price

TI__Guru** 105760 points

Hello Sid,

I would apply enough current to get at least a few mV on the SRN and SRP pins. Usually we recommend 1-2A with a 1mOhm sense resistor.

You may have to reduce the sense resistor if the calibration fails since this is much larger than the expected sense resistor value.

Sincerely,

Wyatt Keller

0 Sid Price over 3 years ago in reply to Wyatt Keller

Prodigy 245 points

OK, will give that a try.

0 Wyatt Keller over 3 years ago in reply to Sid Price

TI__Guru** 105760 points

Hello Sid,

The same current should be applied for the RDR cycle, as specified in the GPCCHEM tool guide (around C/10).

Sincerely,

Wyatt Keller

0 Sid Price over 3 years ago in reply to Wyatt Keller

Prodigy 245 points

Hello Wyatt,

I completed the RDR test and submitted the logs to the ChemID site. As expected, there was no close match found. I do not appear to be able to attach the log file or the report here. How do you suggest we proceed to move forward?

Sid

0 Wyatt Keller over 3 years ago in reply to Sid Price

TI__Guru** 105760 points

Hello Sid,

Can you share the data logs you captured and the report information?

You can send me a private message to discuss the chem ID process.

Sincerely,

Wyatt Keller

0 Sid Price over 3 years ago in reply to Wyatt Keller

Prodigy 245 points

I don't see a way to upload files on this thread,

Sid

0 Wyatt Keller over 3 years ago in reply to Sid Price

TI__Guru** 105760 points

Hello Sid,

Sorry I misread your last message, you should be able to upload by going to insert>image/video/file.

We can discuss in private chat.

Sincerely,

Wyatt Keller

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BQ27Z561-R2: CHEMID for LTO single cell battery