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LM22670: EN pin.

Kengo.Y
Guru 10575 points
Part Number: LM22670

Hi team,

My customer added a capacitor and register to ENpin.
This is to put in an additional soft start.


Are there any concerns about this?

Sincerely.
Kengo.

  • 0
    TI__Mastermind 27030 points

    HI

    the capacitor at EN pin can help filter the noise of EN, but I don't see it help on additional soft start, and what's the value of this cap? I suggest it below 1nF.

    Thanks

  • 0 in reply to Daniel Li14
    Guru 10575 points

    Hi,

    Thank you for your reply.

    C=0.01uF
    R=750kΩ

    Is it OK if I put in resistance?

    Sincerely.
    Kengo.

  • 0 in reply to Kengo.Y
    TI__Mastermind 27030 points

    Hi Kengo:

    where you plan to put the resistance? and what's the purpose for adding filter at EN?

    Thanks

  • 0 in reply to Daniel Li14
    Guru 10575 points

    Hi Daniel,

    The resistance put in between ENpin to GND.
    Because there is chattering across to the UVLO.
    R and C have improved this.
    but despite the presence of Vin, the voltage of the EN pin decreases, and the power is turned off.

    Is it related to the pull-up resistor that is internally connected to Vin?
    How much value is the pull-up register?

    Sincerely.
    Kengo.

  • +1 in reply to Kengo.Y
    TI__Mastermind 27030 points

    HI

    the internal pull-up is a 6uA current source . with 470k resistor, the EN voltage only can hold at 2.82V, Over 2.82V, the internal current will consume by the resistor. 

    if you follow datasheet, actually 470K resistor is connect between Vin and EN to provide extra current to stabilize the UVLO voltage. 

    suggest you can use two up and down resistor connect Vin to UVLO and UVLO and GND to configure the UVLO function. following 7.3.1 Precision Enable and UVLO.

    you can add a capacitor between UVLO and GND to filter the noise, 10nF should be OK

    Thanks