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TPS2413 noise

Timothy Starr
Expert 2445 points
Other Parts Discussed in Thread: TPS2413, TPS2412, TPS2410

In using the TPS2413 we noticed that, even when the FET should be off, the gate pin is ramping and causing glitches of current intot he system. See attached screen shot.

For scope clarification:

Yellow = Input Power (AC Coupled)

Blue = Input current

Purple = "gate" pin on TPS2413 device.

Is this normal? What can be done to have the FET fully OFF? Thanks and Best Regards,

-Tim Starr on behalf of JE@HW

  • 0
    TI__Genius 9415 points

    Please send a schematic. What is the dc loading? how much decoupling on the load?  What is the value of RSET?

  • 0 in reply to Bob Kando
    Expert 2445 points

    Hi Bob-

    Schematic is atached. DC loading is 24mA. Supply must be quiet at light loads. Rset is shorted out. Decoupling is 80uF. Thanks.

    We are considering the TPS2412 due to its linear control. Might this help?

    -Tim

    Bat_Switch.pdf
  • 0 in reply to Timothy Starr
    TI__Genius 9415 points

    The hysteresis controller, TPS2413 is usually the better choice for light loads.

    An RSET resistor may help, you can experiment here. I would start off 100K to 200K. This range is slightly negative to slightly positive shutdown voltage.

    The diodes D32 and D34 should be low leakage. The leakage can work with the 100k resistor and effect the pin C voltage.

  • 0 in reply to Bob Kando
    Expert 2445 points

    Hi again-

    We thought we had fixed this probem by setting RSET to a particular value to decrease the turn-off voltage.

    However, we just read this app note and need clarification:

     

    Although the fast turn-off threshold voltage is resistor programmable at the RSET pin, it is not

    recommended for use in the TPS2410/12. A no-connect at the RSET pin defaults the fast turn-off

    threshold of VAC to 3 mV. This small positive value assures no reverse current into a failed power supply.

    The slightly positive VAC is preferable while the MOSFET gate is in the weak pull-down region and the

    MOSFET is still conductive.

     

    The above comes from section 3.1 of the link below:

    http://www.ti.com/lit/an/slua417/slua417.pdf

    It seems to be saying that using an RSET is not recommended. Could you clarify this with regard to the problem we were having? Thanks and Best Regarrds,

    -Tim Starr on behalf of JH@HW