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BQ78350-R2-DEVICE-FW: PCHG FET how to acivate it when CUV is reached. CHG FET stays active.

rens van bolderik
Intellectual 396 points

Part Number: BQ78350-R2-DEVICE-FW

Hello,

I have drained the battery pack below CUV and saw DSG poort switching off and the CUV flag is activated.
The CUV Threshold is set at 2300mV and Recovery is set at 2600mV.

The FET options bit PCHG is set. The PCHG Fet is not become active and the CHG FET stays active.
Altough I was expecting that the PCHG FET should be come active and CHG FET to be switched off.

I played around with several bit toggled on an off without positive effect.

pchgX125.zip

I have read the RTM but it is not clear to me how to get it operating correctly what do i miss here ?

Kind regards
Rens

  • 0
    TI__Guru* 81034 points

    Hi Rens,

    I experimented with your settings on an EVM. I can reproduce the behavior, but I think I see what is specifically going on.

    First, the CUV and PCHG features are separate and do not affect one another. So CUV will trigger at your setting or 2300mV and will recover at 2600mV (and with charging since you have the [CUV_RECOV_CHG] bit set in Protections Configuration.

    For Pre-charging and Fast charging, your settings are 2000mV for the Precharge Start Voltage and 2400mV for Charging Voltage Low.

    The Pre-charging feature works as described in the TRM when charging from all cells at a lower voltage. If all cells are lower than 2400mV, the PCHG FET is on and the CHG FET will not turn on until all cell voltage rise above 2400mV.

    However, the behavior is a little different on the way down. If one of the cells goes below 2400mV, the CHG FET remains enabled. The device does not switch into pre-charge mode until all of the cells are below 2400mV. I think this is what you are observing.

    Let me know if this makes sense.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 396 points

    Hello Matt ,

    Thanks for your swift response on this and your clear explanation. I have drained my batteries all below 2000mV.

    I did this draining wit by passing the discharge FET(for test purposes only).
    Indeed now the Prcharge FET is enabled and charge FET is switched off and it switched over from pre-charge to charge after all cells reached 2400mVolt.

     

    kind regards
    Rens