BQ34Z100-R2: Current shunt resistor value and SOC jump at rest

Etienne Mandeville

Part Number: BQ34Z100-R2

Tool/software:

Hello,

I’m currently working on a project that uses the BQ34Z100-R2 fuel gauge to monitor the state of charge of a 15S1P LiFePO₄ battery pack. I’ve successfully completed the learning cycle and generated the corresponding golden image file. However, I’m noticing SOC jumps of up to 10% while the system is at rest. The ChemID file was provided by the TI ChemID team.

The board is designed with a 1 mΩ shunt resistor for current measurement, and I’m beginning to suspect this may be related to the behavior I'm observing. I came across a forum post (TI E2E link) where it was mentioned that the minimum recommended shunt resistor value should be 5 mΩ. However, the reference design for the BQ34Z100-R2 uses a 1 mΩ resistor which seems to be contradicting the Technical Reference Manual.

Could you clarify what the minimum shunt resistor value should be for a system with a rest current of around 30 mA? Additionally, could the use of a 1 mΩ resistor be contributing to the SOC jumps I’m seeing during rest?

Best regards,

Etienne Mandeville

2 months ago

0 Alan Frias 2 months ago

TI__Mastermind 25225 points

Hello Etienne,

This question has been assigned and will be responded when possible.

Thank you,
Alan

0 Diego 2 months ago in reply to Alan Frias

TI__Mastermind 25655 points

Hi Etienne,

Typically, we do not recommend going below 1mohm. However, I have seen applications use 500uohm sense resistors if necessary.

With that being said typically sense resistor size is not a contributing factor to SOC jumps. There is a bit "Lock 0", enabling this will prevent soc jumps during rest.

Regards,

Diego

0 Etienne Mandeville 2 months ago in reply to Diego

Prodigy 16 points

Hi TI Team,

Thank you for your prompt response and the helpful clarification.

Currently, "Lock 0" is not enabled in my configuration. I’ll make the necessary adjustments and proceed with further testing. I'll mark this issue as resolved accordingly.

Best,
Etienne

0 Diego 2 months ago in reply to Etienne Mandeville

TI__Mastermind 25655 points

Hi Etienne,

Sounds good!

Regards,

Diego

0 Etienne Mandeville 2 months ago in reply to Diego

Prodigy 16 points

Hi Diego,

I'm still in the process of testing the "Lock_0" configuration change and expect to provide feedback early next week.

In the meantime, I wanted to confirm something with you: it appears that the shunt resistor value will be changed from 1 mΩ to 2 mΩ to address a separate issue. Could you please confirm whether it's sufficient to simply re-do the current calibration, and that a new learning cycle is not required?

Best,
Etienne

0 Diego 2 months ago in reply to Etienne Mandeville

TI__Mastermind 25655 points

Hi Etienne,

No problem, provide the data once available.

You are correct you can swap the sense resistor and recalibrate, no other changes will need to be made.

Regards,

Diego

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BQ34Z100-R2: Current shunt resistor value and SOC jump at rest