BQ77908A: Cell balancing for LiFePo4 (4s)

Lukasz Przenioslo

Part Number: BQ77908A
Other Parts Discussed in Thread: BQ34Z100-G1, BQ40Z50-R2, EV2400, BQ40Z50, BQ4050

Hello there,

We are currently looking for an autonomous (or semi-autonomous) cell balancing IC that could be used with a 4s LiFePo4 chemistry cells. We have decided to use the bq34z100-g1 for gauging and considering the bq77908A for balancing and protection. Issue is that it seems that this IC is intended for Li-Ion and Li-Polymer packs.

Question is- can the IC be used with LiFePo4 after the registers are adjusted?

If there is a better fit for this in the TI portfolio, I would appreciate the suggestion. We are considering using an MCU that would be a data collection node for the bq34z100-g1 and the cell balancing IC, before the end data is exposed to the end system (for instance the if the balancing algorithm would not be fully automated). If possible however, it would be best to not use any additional MCU's...

I would appreciate all feedback and suggestions.

over 2 years ago

0 Luis H. S. over 2 years ago

TI__Mastermind 32340 points

Hello Lukasz,

You should be able to balance LFP cells using the BQ77908A. The IC does not know type of chemistry of the battery, it will only monitor the voltage. As long as the cell balance thresholds align with what you need, it should work after adjusting the registers.

Some of our gauges may be good fit for your requirements, like the BQ40Z50-R2 (has LFP support), which offers gauging, cell balancing and protection features for up-to 4 cells. An additional MCU should not be needed.

Best Regards,

Luis Hernandez Salomon

0 Lukasz Przenioslo over 2 years ago in reply to Luis H. S.

Expert 2630 points

Hi Luis,

Thabks for the feedback, looks interesting. The SMBus seems to be a drawback- is it compatible with i2c?

0 Lukasz Przenioslo over 2 years ago in reply to Luis H. S.

Expert 2630 points

Actually already found the answer, all should be good... Do you know whether eval boards are available for purchase?

+1 Luis H. S. over 2 years ago in reply to Lukasz Przenioslo

TI__Mastermind 32340 points

Hello Lukasz,

Yes, it does seem to be in stock. See the BQ40Z50EVM page.

The EVMs for our products are usually displayed in the product page of each IC, if available. Usually found in Design & development>Hardware Development.

Best Regards,

Luis Hernandez Salomon

0 Lukasz Przenioslo over 2 years ago in reply to Luis H. S.

Expert 2630 points

Thanks for the info. Could you only confirm whether the EV2300 is suitable for communicating with the eval, or another tool is needed?

0 Luis H. S. over 2 years ago in reply to Lukasz Przenioslo

TI__Mastermind 32340 points

Lukasz,

No problem! It is recommended to use the EV2400 to communicate with the newer gauges, use this.

If using the EV2300, the gauge may not be able to communicate.

Best Regards,

Luis Hernandez Salomon

0 Lukasz Przenioslo over 2 years ago in reply to Luis H. S.

Expert 2630 points

Hi Luis,

We have now ordered the Texas Instruments BQ4050 Development Kit, which I just noticed has a slightly different part number (BQ4050 instead of the BQ40z50, i.e. this one BQ40Z50EVM-561).

Could you please let me know what is the difference between the 2 IC's (with Z and without Z inside of its ID)?

0 Luis H. S. over 2 years ago in reply to Lukasz Przenioslo

TI__Mastermind 32340 points

Hello Lukasz,

The main difference is that the BQ4050 uses CEDV gauging algorithm, while the BQ40Z50 uses the impedance tracking algorithm, which provides more accurate gauging over temperature. Most of the recent updates/features are also found in the BQ40Z50.

Best Regards,

Luis Hernandez Salomon

0 Lukasz Przenioslo over 2 years ago in reply to Luis H. S.

Expert 2630 points

Understood, thank you. So I understand that from the evaluation perspective the registers set differs?

0 Lukasz Przenioslo over 2 years ago in reply to Luis H. S.

Expert 2630 points

Also Luis, do you know whether its ok to desolder the 4050 from the 4050 eval voard and solder the 40z50 ic? Are the evals and ics identical in case of layour and connections?

0 Luis H. S. over 2 years ago in reply to Lukasz Przenioslo

TI__Mastermind 32340 points

Hello Lukasz,

I am not fully aware if there are differences, but from briefly looking at the pages for each, the layouts seem identical. So I would assume that you could simply solder the BQ40Z50 on the board. Double check with the BOM of both by looking in the EVM User Guides for each.

Best Regards,

Luis Hernandez Salomon

0 Luis H. S. over 2 years ago in reply to Luis H. S.

TI__Mastermind 32340 points

Hello Lukasz,

I forgot to answer your first question.

The registers and code for each IC probably would differ a significant amount.

Best Regards,

Luis Hernandez Salomon

0 Lukasz Przenioslo over 2 years ago in reply to Luis H. S.

Expert 2630 points

Noted, thanks Luis

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BQ77908A: Cell balancing for LiFePo4 (4s)