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TPS548D22: Enable Pin Functions Consult

Stanley Dai
Expert 5810 points
Part Number: TPS548D22
Other Parts Discussed in Thread: TPS53353, TPS53355

Hi Team,

Customer wants to add R-C network for delaying Enable signal for our TPS548D22/ TPS53353 / TPS53355. They want to know do we have any slew rate or source/sink current requirements for enable pin? or our device just monitor the threshold voltage on Enable pin here. Thanks.

Best,

Stanley

  • 0
    TI__Guru 56985 points

     

    We are not aware of a slew-rate limitation on the EN pins of the TPS548D22 / TPS53353 / TPS53355, however these devices have internal pull-up resistors from their EN pins to their internal regulators so that the EN pins will pull up and turn on the device if the EN pin is allowed to float.

    We will need to check on the exact resistance for each device.

  • 0 in reply to Peter James Miller
    TI__Expert 5810 points

    Peter,

    Pls help us check the detailed design of EN pins. Customer plans to control the slew rate of EN pin voltage by using R-C network. In this way, they can further delay device power-on. 

    The key considerations here for customer are any potential risks for this proposal? Thanks.

  • +1 in reply to Stanley Dai
    TI__Guru 56985 points

     

    Yes, I understand your use model.  The primary potential risk is that the series resistor would limit the pull-down strength and prevent proper turn-off, or that the internal pull-up would compromise the targeted delay time by over-driving the attached filter resistor.

    The most reliable delay timing method would be to add an external pull-up resistor to regulator bypass pin (BP or VREG), then use an open-drain logic signal to drive the pin voltage to ground.  On release, the external pull-up resistor and internal resistor will both pull up on EN until the voltage rises to its threshold.  An external pull-up resistor of 10-20kΩ would minimize any influence from the internal pull-up.

    If the open-drain pull-down is limited in voltage, to say, 3.3V, a second resistor to ground can limit the voltage on the pin without compromising performance.

    The EN to GND capacitor can then be selected to provide the correct delay timing.  The tolerance on the EN threshold voltage (1.45V - 1.75V) along with the capacitor tolerance will drive most of the timing error.