BQ27520-G4: Compatibility with LiFePO4 Cells

Antonio Fadhel

Part Number: BQ27520-G4
Other Parts Discussed in Thread: BQ27Z561-R2, BQ34Z100-G1, BQ27742-G1, BQ34110, BQ27220

Hi,

I am looking for a system-side gauge for single cell LiFePO4. The BQ27520-G4 seems like it would work since it is flash-based with programmable ChemID, but the parametrics table does not list it as LiFePO4 compatible. The supply voltage range (2.45V min with no flash writes) seems adequate.

Is there a reason why it wouldn't be compatible?

Thanks,

Antonio

over 3 years ago

0 Wyatt Keller over 3 years ago

TI__Guru** 102955 points

Hello Antonio,

We have specific algorithms in the bq40z40-r3 and bq27z561-r2, for examples, that support LiFePO4 chemistries. If you take a look at the gauges I mentioned they have LFPrelax in the TRM, this algorithm helps with the Qmax updates and OCV measurements for the LiFePO4 characteristics.

Sincerely,

Wyatt Keller

0 Antonio Fadhel over 3 years ago in reply to Wyatt Keller

TI__Genius 9410 points

Hi Wyatt,

The issue with those two devices is that they are pack-side gauges. I am looking for system (host) side, and the BQ27520-G4 seems to be the only one that would work aside from a multicell gauge such as BQ34Z100-G1 which would be overkill.

Can you confirm if there would be any issues with BQ27520-G4?

Thanks,

Antonio

0 Nick Brylski over 3 years ago in reply to Antonio Fadhel

TI__Mastermind 19195 points

Hi Antonio,

For LiFePO4 bq27520-g4 is not a good fit.. It does not have the LFP_relax function.

Bq27z561-r2 or bq27742-G1 are the best options for 1s lifepo4.

0 Antonio Fadhel over 3 years ago in reply to Nick Brylski

TI__Genius 9410 points

Hi Nick,

Per my message above, I am looking for a system-side gauge. These are listed as pack-side gauges, i.e. gauges that require the same cell to be tied to the gauge. Pack side gauges do not allow for user replaceable cells.

What would be the impact of using a gauge with a LiFePO4 ChemID but without the LFP_relax feature?

Thanks,

Antonio

0 Nick Brylski over 3 years ago in reply to Antonio Fadhel

TI__Mastermind 19195 points

Hi Antonio,

The gauge could take OCV measurements when the voltage profile is very flat causing massive error in DOD, basically shifting the OCV and Resistance curves

Please cosnider bq34110 or bq34z100-g1

Thanks,

0 Antonio Fadhel over 3 years ago in reply to Nick Brylski

TI__Genius 9410 points

Thanks, Nick. I will look into bq34z100-G1 for now. If adding the LFP_relax feature to the BQ27520-G4 would be just a FW update, it would make sense to look into it so that we have a dedicated single-cell system-side gauge for these applications.

Regards,

Antonio

0 Nick Brylski over 3 years ago in reply to Antonio Fadhel

TI__Mastermind 19195 points

Hi Antonio,

The bq27220 CEDV gauge can support LiFePO4 and is system side. The LFP_relax feature is needed for impedance track gauge supporting LiFePO4 chemistry.

Some more discussion here: e2e.ti.com/.../606287

Best regards,

Power management

Power management forum

BQ27520-G4: Compatibility with LiFePO4 Cells