BQ79606A-Q1: BQ79606Q1 Report SM130 fault under low temperature.

Hello,

I apologize for the delayed response. I am working on answering your question soon as I can.

Thank you,

Zachary

Hi Zachary:

Have you got any progress on this issues?

Best Regards

Hi Zizhen,

I apologize for the delayed reply. When you test at low temperature, do you decrease the temperature of just the IC or the entire system, batteries included? Low temperature should decrease the Rdson of the CBFET, not increase, so the silicon doesn't explain why you are seeing a decrease in voltage change.

Thank you,
Zachary

Hi Zachary:

we decrease the temperature of the entire system. 

Besides, the Rdson of the CBFET would not have impact on SM130, bescasue SM130 will not control the CBFET.

As you can see in the last picture, the measured value of cell voltage increases as the temperature decreases, and the measure value when enable current sink and current source begins to oscillate as the temperature decreases, and the delta voltage decreases as the temperature decreases.

whether this could be a question of measurement accuracy. The measurement accuracy which described in the data sheet as decreasing as the temperature decreases.

Thankyou.

Zizhen

Hi Zizhen,

Are you able to cool just the IC and see if the same results are seen? Furthermore, I don't fully understand all your data. Are the battery cell voltages being monitored with an external DMM and then compared to the IC's measurements? The expected accuracy at your temperature and voltage is: –4.46 to 3.77mV, and you are saying that this is not what is being observed?

I apologize for the delayed responses, I will try to respond as promptly as I can.

Best,

Zachary

Hi Zachary:

Currently, only cooling IC at low temperature and keep it for us is too difficult.

About the data, as you can see the picture:

the temperature(signals: Meas_cb_temp_0_ST3 and Meas_cb_temp_1_ST3) decrease from 25℃ to -39℃, but the measured cell voltage(CellVolt::_0_ and CellVolt::_1_) increase from 3377mV to 3380mV. and the measure value(CellVolt_OC::_0_ and CellVolt_OC::_1_) when enable current sink and current source begins to increase and oscillate as the temperature decreases, then the delta voltage of cell1(different between CellVolt_OC::_0_ and CellVolt::_0_) is also unstable.

Best Regards

Zizhen.

Hi Zachary:

Forgot one point in the reply above.

The cell voltage is supplied by a voltage regulator, it would not change and oscillate.

Hi Zizhen,

So I believe the issue here is that when you are enabling current sinks and sources, this is causing voltage differences in the ADC readings. This is being made worse at low temperatures due to the cooling of the silicon changing both the current sources and ADC measurements. Essentially accurate cell voltage measurements cannot be made during current source/ current sinks being enabled. These two actions need to be done separately. 

Thank you,

Zachary

Hi Zachary:

Thank you for feedback. So the low temperature will make the silicon measure accuracy more worse, right?

We enable current source/current sink just want to implement SM130 diagnose according to safety manual.

Hello Zizhen,

Temperature can have a strong effect on the ADC accuracy. The big factor here is to ensure that ADC readings are made without sinks and sources being enabled. This will make sure that the readings are accurate. As you can see in the manual, there is a wait time after disabling the sinks and sources so that this doesn't have an effect on ADC readings. ADC results should be accurate following this process.

Best,

Zachary

Hi Zachary:

As you can see in the process of SM130, the result B is the measured value of cell voltage after enable current source and current sink. and the problem is the result B isn't accurate.

Best Regards

Zizhen.

Hi Zizhen,

I will talk with my colleagues about this to see if they have any opinions and will get back to you after the weekend.

Thank you,

Zachary