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TPS22990: Schematic Review

Bill Kury
Prodigy 220 points
Part Number: TPS22990

Could you please review the following schematic:TPS22990 Inrush controller.docx

  • 0
    TI__Mastermind 32650 points

    Hi Bill,

    Please make sure the CT cap is rated for 25V. 

    By tying ON to VIN and VBIAS you will not get the expected timing result. This is because the startup sequence can finish before the voltage rail ramps up if the 3.3V rail ramps slowly. Timing will be affected and thus the inrush clamping will be affected as well. I would recommend you test this using our EVM to make sure the performance is acceptable.

    Finally, I would recommend using a pull down resistor on the ON pin to make sure that the rail is pulled to GND when 3.3V is turned OFF.

    Thanks,

    Shreyas

  • 0 in reply to Shreyas Dmello
    Prodigy 220 points

    This device will used as the in rush control on a plug in module.  The internal circuitry of module will not be powered at plug in.  What would be the best way to connect the on pin so that power flows through the device at plug in?  

    Bill

  • +1 in reply to Bill Kury
    TI__Mastermind 32650 points

    Hi Bill,

    It is acceptable to connect the on pin to VIN as you have but this will affect the timing of the device. Ideally, the system works with the VIN/VBIAS input being separate from a controller input to the ON pin. This is how the device has be characterized and validated from a timing perspective as the rise time is defined as the the time between the output rising from 10% to 80% of the input.

    The soft start circuitry allows for a linear rise but in your situation, the references of 10% and 80% are changing since VIN/VBIAS is ramping up. As such, you will see some timing variation from the datasheet and the calculations for CT capacitance will not be exact. Through testing you can find the right amount of CT capacitance to use for your system. My only recommendation is to add a pull down resistor to the ON pin so that it discharges the ON pin during turn off as floating voltages here could lead to undesirable behavior.

    Thanks,

    Shreyas