BQ29209: Overvoltage Hysteresis is not compliant with data sheet

Hello Stefano,

I've tested on our board before (When I confirmed that OVP disabled cell balancing) and found the OV hysteresis was accurate to the datasheet spec (~300-mV). I would trigger OVP at ~4.3-V and it recovered (OUT low) at ~4.0-V.

Do you see this on a different part? Are you measuring directly at the input pins?

Best Regards,

Luis Hernandez Salomon

Hi Luis,

 I read on the top of the component:

209
TI 191
A6DP

Then I suppose that the component is right and the measure is directly on the input pin

I've check also on the other PCBA and the result is the same

BR

Stefano

Hello Stefano,

Have you tried using other ICs to see if it's the same?

Could you also describe what is the Q5/Q4 circuit? Can this be affecting the voltage reading somehow?

Best Regards,

Luis Hernandez Salomon

Hello Luis,

Luis H. S. said:

Could you also describe what is the Q5/Q4 circuit?

Are the external mos for increasing balance current,R4 is not mounted 

Luis H. S. said:

Have you tried using other ICs to see if it's the same?

Stefano Sivera said:

I've check also on the other PCBA and the result is the same

Luis H. S. said:

Can this be affecting the voltage reading somehow?

The second PCBA checked is without external mos.

Best Regards

Stefan o 

Hello Stefano,

I understand the circuit now. I see you tested in another PCB, but did you test using multiple ICs? It would be good to confirm also if they have different markings.

Could you also describe you're exact testing sequence and how it was measured/tested? I want to try it from my side with our part.

Best Regards,

Luis Hernandez Salomon

Hello Luis,

 the other IC is marked:
209
TI 191
A5DP

About the sequence:

- using 2 batteries with 3650mV and 4250mV 
- connect the charger that start in CC at 100mA
- when the higher battery reach 4295mV OUT go high 
- connect a load directly to the battery with a 50/100mA CC
- the battery voltage decrease
- when it reach 4230mV OUT go low

More simple sequence.

Best Regards

Stefano Sivera

Hello Stefano,

Thank you for the sequence!

I will be checking it out tomorrow and tell you if I see anything different. I apologize for the wait, today I unfortunately did not have time to go through it.

Meanwhile could you test with a power supply just to make sure all is okay?

Best Regards,

Luis Hernandez Salomon

Hello Luis,

Luis H. S. said:

Meanwhile could you test with a power supply just to make sure all is okay?

I don't understand what do you mean.

Stefano 

Hello Stefano,

I meant that if you could test on your board using power supplies for the cell inputs instead of using real batteries. Then change the power supply voltage to OVP and down to see when it recovers.

Do this test on the board without the external FETs just to confirm and cell balancing disabled so it does not affect anything.

I recreated your test sequence in our board with two power supplies and two resistors. I connected 1-kOhm across each cell input, from VC2 to VC1 and VC1 to Vss, and I put a power supply for each in order to adjust their individual voltages. I performed the test in the following ways:

• Cell balancing ENABLED:
  • VC2 = ~4.235-V, VC1 = ~3.65-V
    • Ramped up VC2 until OVP triggers (~4.3-V). OUT goes HIGH.
    • Lowered VC2 voltage until device recovers (~4.0-V). OUT goes LOW.
  • VC2 = ~3.6-V, VC1 = ~4.235-V.
    • Ramped up VC1 until OVP triggers (~4.3-V). OUT goes HIGH.
    • Lowered VC1 voltage until device recovers (~4.0-V). OUT goes LOW.
• Cell Balancing DISABLED:
  • VC2 = ~4.235-V, VC1 = ~3.65-V
    • Ramped up VC2 until OVP triggers (~4.3-V). OUT goes HIGH.
    • Lowered VC2 voltage until device recovers (~4.0-V). OUT goes LOW.
  • VC2 = ~3.6-V, VC1 = ~4.235-V.
    • Ramped up VC1 until OVP triggers (~4.3-V). OUT goes HIGH.
    • Lowered VC1 voltage until device recovers (~4.0-V). OUT goes LOW.

In all cases I saw the hysteresis working as intended.

Best Regards,

Luis Hernandez Salomon

Hello Luis, understood about power supply, I doing the test and effectively in this way the hyst. is 300mV. I fon't understand what changes with the battery, I have also verify with the scope  and there is not transition voltage on the real battery.

Best Regards

Stefano 

Hello Stefano,

Could you try adding large capacitors across the battery cells and charge/discharge the battery? It could be that when you apply a load the voltage of the cell is dipping enough to get out of OVP.

Best Regards,

Luis Hernandez Salomon