Pls give examples on how to apply V-uS stated in datasheet

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powersys

Joined: 29 Nov 2005
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02 Nov 2006 11:27 Pls give examples on how to apply V-uS stated in datasheet

In the datasheets of some inductors, V-uS of the inductor is given. Pls give examples on how to apply the V-uS value in the design of a switching power supplies. Thanks.

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VVV

Joined: 26 Nov 2004
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03 Nov 2006 18:26 Re: Pls give examples on how to apply V-uS stated in datashe

Assume you have to design a buck regulator. You have established the frequency (or it's fixed, such as for some integrated regulators).
Then you need to select an inductor. You find the right inductance, but how do you know if it will not saturate when driven?
In other words, how do you know the inductor can store the required energy, which really means that the core is sufficiently large?

You calculate the actual V*us for the worst case, which is the highest input voltage, zero output voltage (at startup or under short-circuit conditions) and the maximum allowable duty-cycle.
Then you compare that value to the V*us rating in the datasheet.

This should not be taken as literally as aove, because most chips actually have current limit circuitry that will limit the duty-cycle when the current reaches a certain level, so you will not actually get into that worst-case situation (that means the duty-cycle will not be at its maximum).

For more info, see appnote AN-1197 from National.