Author Topic: Find max dcdc reg output current when datasheet only gives peak inductor current  (Read 397 times)

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Offline PsiTopic starter

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If I have a monolithic dcdc reg and the datasheet does not give a max output current but does have a peak inductor current limit, how can I figure out what the chips max output current is. (Assuming adequate cooling/chip temp of cause)
I assume the peak inductor current is not the same as max output current.

The chip i'm looking at has a built in max peak current limit of 4.33 A or 6.5A depending on version.
And i'm trying to figure out if it would be usable for 9-16V in  and 9-16V out at 3A  (sepic)

https://www.ti.com/lit/gpn/LM5157

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Offline bob91343

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Without knowing any details, I would assume that the peak inductor current needs to be multiplied by the duty cycle to determine steady current.  Actually, this would only be true if inductor current were square.  If inductor current is caused by a square voltage, then it's a triangle wave and its resultant dc would be less, no more than 1/3 of the peak, times the duty cycle.  All this, neglecting abberrations such as spikes.
 

Offline PsiTopic starter

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yeah, i figured there must be a way to calculate it, i just have no idea how.

But taking the duty cycle into account makes sense.
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Online David Hess

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The peak current is never less than the output current and it approaches the output current as the inductor ripple current approaches zero.  Otherwise in continuous conduction mode:

Ipeak = Iout + Dcycle(Vin-Vout)/(2LF)

Linear Technology application note 19 discusses the parameters for the various switching topologies.
 


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