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LMR54410: behaviour of EN

Olrik Maier
Expert 4780 points
Part Number: LMR54410
Other Parts Discussed in Thread: LM2575, LM46002

Dear Power Experts,

we are looking into the LMR54410 with my customer to build a controled DCDC which can be switched on and off. Plan for this is to use the EN pin.

In the DS I found for soft start:

Soft start is achieved by slowly ramping up the internal reference voltage when the device is first enabled or powered up. The typical soft-start time is 1.8 ms.

Does this mean that the soft start function is only at the first enable or at every enable. The part in our application is powered on and the switched on and of with the EN pin. Does the part do a softstart every time if the part is disabled and enabeled again with the EN pin ?

In the Webench simulation it looks like that the softstart occurs at every switch on with the EN pin.

What is an alternative part which has no softstart function when using EN to switch on and off.

Best wishes,

Olrik

  • 0
    TI__Guru 64085 points

    Hello

    Yes, the device will go into soft-start at every turn-on and off of EN.

    I am not sure if we have any devices without soft-start.  The 1.8ms is on the short side.

    Maybe some of our very old devices such as the LM2575 may not have soft-start.

    However, you would get a large inrush current.

    You may be able to use a device with a external soft-start pin and try to connect that

    pin to the VCC pin of the regulator.  However, that would be a highly experimental proposition.

    Thanks

  • 0 in reply to Frank De Stasi
    TI__Expert 4780 points

    HI Frank,

    do we have MV parts with seperate softstart pin ?

    Have found TPS6290x series but it's only 18Vmax input - we need higher input voltage robustness  approx 20V.

    Best wishes,

    Olrik

    -

  • 0 in reply to Olrik Maier
    TI__Guru 64085 points

    Hello

    We have HV devices with a SS pin.

    But they only allow to increase the SS.

    LM46002, etc.

    Thanks