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TPS22975: Upper limit of CT capacitance

Part Number: TPS22975

Hi Team,

Since the rise time can be controlled with the CT of TPS22975, we are considering a rise time of about 10 seconds. Vin is 5V.
However according to the "Table 1. Rise Time tR vs CT Capacitor" on datasheet, the max rise time listed is just 16980µs.
Is there an upper limit for the capacitance of CT that determines the rise time of the TPS22975? What capacitance shoud be used if Rise Time is 10S. I was thinking about 1uF but I do not know whether it is good or bad because it is not on the table.

Beat Regards,
Tom Liu

  • Hi Liu,

    You can use the Equation 1 on the TPS22975 datasheet to calculate the slew rate for a capacitance. I believe a 5V rail over 10s would require a large capacitance like 4.5uF. This is a very slow turn on phase.

    There is no upper limit for the capacitance used but the inrush current that is meant to be reduced during this phase is another factor to consider.

    For example, if the load capacitance was so large that 1A of current would flow through for 10s during turn on, the thermals of the system have to be compatible. During turn on, the resistance of the FET is slowly decreased to make sure that the inrush is clamped.