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BQ78350-R1: CTOS flag

vinay kambappa
Prodigy 160 points
Part Number: BQ78350-R1

When I turn on the FET by using FET_EN it doesn't turn on the FETs (erratic behavior). But if I use DSG_FET_toggle and CHG_FET_Toggle it turns on. Also while charging the pack at 3A after few minutes the Fets turn off with CTOS flag set.The CTO threshold is 2500mA, I wanted to know if this value needs to be set more than the charging max current? But I had not experienced the same behavior earlier without making any changes to CTO parameters.

This is the wave form across gate and source of discharge FET,when enabled using FET_enable.The only difference between FET_enable and DSG_Toggle is that in FET_EN enables both CHG_FET and DSG_FET are turned on simultaneously.

\

This is when DSG_Toggle was used.

  • 0
    TI__Guru* 81034 points

    Hi Vinay,

    I do not recommend using the FET Test commands like CHG_FET_TOGGLE and DSG_FET_TOGGLE. These are intended for testing the FETs during manufacturing but not for operation in the application. The FET_EN bit is the correct way to enable the FETs.

    The FETs will be disabled if there is a protection that triggers them to turn off. You might want to collect a log file of this behavior that includes all of the Safety Alert and Safety Status registers. The CTOS threshold might be okay, but what is the CTOS duration time set to? This protection is to prevent charging longer than a set amount of time.

    Best regards,

    Matt