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BQ76952: Readout cell voltage is under UV threshold but protection not work

Aska Tseng
Prodigy 20 points
Part Number: BQ76952

Tool/software:

Hi,
The VU protection not work follow the below steps. UV protection is activated. (Settings / Protection / Enabled Protection A / Bit 2 Enable)

1.Power supply set 16 cells voltage to 2380mV.
2.Modify cell 2 voltage gain from 12122 to 11000, let read out voltage become 2143mV.
3.UV threshold is 44*50.6 = 2226.4mV
4.Min cell voltage is 2143mV which under threshold of UV but UV portection flag not acitve.

It seems that the condition for triggering UV is not based on the value read back.
What is the UV protection trigger conditions?

best regards,

Aska

  • 0
    TI__Intellectual 1140 points

    Hello,

    1. Delay on the device

    The device must go over the voltage threshold for at least the time of the delay in order for the protection flag to be triggered. For example, if the delay is 2 seconds, then the measured voltage must be above the threshold for 2 seconds to be triggered. Make sure the delay is not too long as that could be a reason as to why you are not seeing any flag being triggered. You can adjust this by going to Protections:CUV:DELAY.

    2. Hysteresis on the device

    The device utilizes the CUV threshold + CUV Hysteresis to recover from a fault. If the hysteresis is too small of a value, the device can easily recover from the fault and you may never see the fault be triggered due to this.

    For more information/details on the Cell Undervoltage Protection trigger conditions, take a look at section 5.2.5 in the TRM.

    Regards,
    Rohin N.

  • 0 in reply to Rohin Nair
    Prodigy 20 points

    Hi Rohin N.,

    Thanks for your reply,

    After modifying the cell voltage gain, CUV protection can work, but the conditions changed,
    must all voltages meet the CUV conditions, not the minimum cell volage. and recovery conditions are minimum voltage greater than CUV threshold + CUV Hysteresis.

    My question is, after modifying the cell voltage gain, the CUV protection conditions does not refer the reported minimum voltage of cell, how does it work? 

    It could be reproduced by the demo board.

    best regards,

    Aska

  • +1 in reply to Aska Tseng
    TI__Intellectual 1140 points

    Hello Aska,

    The conditions for the CUV protection are not modified when altering cell voltage gain.

    However, just to clarify, CUV protection uses a hardware comparator to monitor the voltage of each cell. The cell voltage measurement comes from the ADC reading, which is also where your cell voltage gain is seen. The hardware comparator (CUV protection) does not use that same cell voltage reading. You may need to calibrate your comparator for this CUV protection.

    Table 7.26 in the datasheet will detail the detection range, threshold accuracy, and delay for the comparator. There are also details for comparator calibration here.

    Please let me know if you have any more questions or anything is unclear.

    Regards,
    Rohin Nair

  • 0 in reply to Rohin Nair
    Prodigy 20 points

    Hi Rohin Nair,
    1.The CUV protection is active by hardware comparator and threshold is controlled by register CUV threshold.
    2.The cell voltage measurement comes from the ADC reading, which is relate setting of cell voltage gain. 
    3.Cell voltage measurement only reports the cell voltage, not involved in the protection function.

    Is my understanding wrong? if so, please correct me. thank you so much.

    best regards,

    Aska

  • 0 in reply to Aska Tseng
    TI__Intellectual 1140 points

    Hello Aska,

    Your understanding is correct!

    Regards,

    Rohin Nair