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BQ40Z50-R2: PFStatus(TS1)

Martin R.
Intellectual 335 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQSTUDIO, BQ40Z50

Hello guys,

I use many bq40z50R2 and sometimes i get after assembling an permanent failure which disables CHG and DSG Fets.

Question:

1. At which condition the PFStatus(TS1) trips? I don't mean PFAlter(TS1)! I can't find any correlation in the TRM.

2. At different boards i get different values: Data Memory(bqStudio) > PF Status > Device Temperature Data > External 1 Temperature: For example -53.8°C or -75.9°C or -32.6°C.
When and how are this values written? Internal and External Thermistor 1 in usage.

Thanks vor help.

  • 0
    TI__Genius 12215 points

    Hi, Martin

        For such low temperature reading, typically, NTC disconnecting could be the cause for it.

        Do you assemble the NTC when the board is powered? If so, you can clear the PF and reprogram the srec file after the NTC is installed on the PCB.

  • 0 in reply to Steven Yao
    Intellectual 335 points

    Yes, thats right. The NTC will be connected after assembling the cell, but the bq40z50 is in Shutdown Mode with disabled FETs. Just at PRES = HIGH wakes up the bq40z50 and at this moment the system shows this PF TS1.

  • 0 in reply to Martin R.
    TI__Genius 12215 points

    Hi, Martin

       How do you send the device in shutdown mode?

       Do you send a shutdown command to the device? If so, before you sending the shutdown command, the extreme low temperature will be detected before sending the shutdown command.

       If you think the device is in shutdown mode before you activate the board by shorting the Pack+ and Bat+, then one thing should be noted is that there is a probability for the device to be awakened by only power up at BAT+ and BAT- w/o the activating operation, as the bypassing cap across the CHG and DSG FETs can momently short Pack+ and Bat+ at the moment when the power is applied to BAT+ and BAT- of the board, it depends on the charge on the bypassing caps which is something out of control during production.

  • 0 in reply to Steven Yao
    Intellectual 335 points

    Thank you so much, Steven.

    That's a usefull information. It seams like the capter 5.5 in the TRM i read actually. I will check it out.

  • 0 in reply to Martin R.
    Intellectual 335 points

    But I think my second question isn't answered.

    Why are the temperature values such random when gauging  the NTC with an broken connection (exatly -53.8°C or -75.9°C or -32.6°C) ? And which influences has these value  (Data Memory(bqStudio) > PF Status > Device Temperature Data)?

  • 0 in reply to Martin R.
    TI__Genius 12215 points

    Hi, Martin

        Can you measure the voltage at the TS1 pin and GND with NTC removed with oscilloscope, I think that waveform could be helpful to identify why such diversity temperatures are reported in those failed devices.

  • 0 in reply to Steven Yao
    Intellectual 335 points

    With connected NTC:

    Without NTC: (^= -53.8°C)

    Seems not very special.

  • 0 in reply to Martin R.
    TI__Genius 12215 points

    Martin

        I also made measurement to TS1 pin with oscilloscope, when the oscilloscope is attached to the pin, the reading is stable, -53.1C. I only observed -70C~75C or -5xc randomly when I remove the probe. This indicates the voltage at the input of TSx is not stable when NTC is not connected.

       Also, per datasheet, the max input for ADC is 0.8xREG, the voltage for the peak of NTC pulse I measured on the scope is 1.7v, it is already out of the input range of the ADC, the output accuracy is unspecified. So the value is not reliable.

  • 0 in reply to Steven Yao
    Intellectual 335 points

    I think this topic is resolved. We are changing some working steps to avoid any faulty messurement from the bq40z50. To begin connecting the NTC, sencond Cell assembling.

    Dear Steven,

    thanks a lot for your detailed and insightfully support. I appreciate your intensice efforts and hope you can help me next time again.

    Best regards,

    Martin

  • 0 in reply to Martin R.
    TI__Genius 12215 points

    Hi, Martin

        It is my pleasure to be able to help you! Happy work and good luck