BQ25750: Battery charge completion issue

Jeevabharathi R

Part Number: BQ25750
Other Parts Discussed in Thread: BQ40Z50

Hi Team,

We are currently using the BQ25750RRVR battery charge controller IC to charge a 4S1P LiFePO4 battery (6000Ah capacity).

We’re encountering an issue where the charge completion status is not being properly indicated.

Observations:

Signals:

Yellow trace: Battery voltage
Blue trace: Battery current

STAT1 / STAT2 pins are toggling continuously.
Battery terminal voltage fluctuates between 13.3V and 15.2V in a repeating cycle.
Battery Open circuit volatge measured during this time is 13.7V.
EN_PFM is set to 0.
Charging current is set to 1.8A (0.3C)

We have previously discussed this issue related to the BQ25750 in the following thread:.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1552579/bq25750evm-the-charging-issue-with-the-bq25750

Note: We have BQ40Z50 Battery Pack Manager in our battery back.

Please help us solving this issue.

Thanks,

Jeevabharathi

5 months ago

0 Jeevabharathi R 5 months ago

Prodigy 160 points

Hi Team,

Please find the attached register value for two consequtive read for this BQ25750 IC during the above mentioned issue.

Note: REG0x21 Register switch between 0x0F and 0x0C

Thanks

Jeevabharathi

0 Ethan Galloway 5 months ago in reply to Jeevabharathi R

TI__Mastermind 35676 points

Hello Jeevabharathi,

In the system, did the battery pack close its charge FETs?

This would mean that the BQ25750 is charging an open circuit.

Can you read the registers of the BQ40Z50?

Best Regards,
Ethan Galloway

0 Jeevabharathi R 5 months ago in reply to Ethan Galloway

Prodigy 160 points

Hi Ethan,

Thanks for your reply,

We were unable to probe the BQ40Z50 FET gate as it is located within the sealed battery pack.

Please find the register value of BQ40Z50.

Kindly review them and assist us in identifying the issue.

0 Ethan Galloway 5 months ago in reply to Jeevabharathi R

TI__Mastermind 35676 points

Hello Jeevabharthi,

Thanks for the new information. I'm looping in the battery gauge experts to analyze the registers.

Best Regards,
Ethan Galloway

0 Miguel Castro Gonzalez 5 months ago in reply to Ethan Galloway

TI__Expert 7904 points

Hello Jeevabharthi,

Based on your screenshot, the CHG FET turned off because safety triggered (SS = 1). I see COV triggered. Please check your COV thresholds.

-Miguel

0 Jeevabharathi R 5 months ago in reply to Miguel Castro Gonzalez

Prodigy 160 points

Hi Miguel

We are not fully familiar with all the resistor-related settings in the BQ40Z50; these values were configured by the battery pack manufacturer.

I have attached the register settings for COV. Could you please confirm if these settings might be causing the issue?

Fig: 1

Additionally, for your reference, sometimes the battery terminates properly without any problems, but at other times we encounter this issue. We are unsure why this inconsistency occurs.

Thanks,

Jeeva

0 Miguel Castro Gonzalez 5 months ago in reply to Jeevabharathi R

TI__Expert 7904 points

You battery COV threshold is too low (3.7V). However, when I see the charger voltage of 15.2V, that would be 3.8V per cell. That means your COV will trigger when charging the battery. What is your expected charger voltage?

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BQ25750: Battery charge completion issue

Observations:

Signals: