x D

13.2V - 1.2V

0.5 MHz x 1 PH

13.2V - 1.2V

500 kHz x 3A

x 0.1 = 0.8 PH

64 x 3.4 m:

500 kHz

x

12V

12V + 2

= 0.4 PH

x

LM3495

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SNVS410F – FEBRUARY 2006 – REVISED APRIL 2013

By calculating in terms of amperes, volts, and megahertz, the inductance value will come out in micro henries.

The second minimum inductance equation specific to the LM3495 is:

(17)

By calculating in terms of milliohms and kilohertz the inductance value will come out in micro henries.

For this design:

(18)

Whichever equation gives the higher value for inductance is the one which should be followed.

The second criterion for selecting an inductor is the peak current carrying capability. This is the level above

which the inductor will saturate. In saturation the inductance drops off severely, often to 20% to 30% of the rated

current. For this example:

(19)

Hence an inductor must be selected that has a peak current rating greater than 11.5A and an average current

rating greater than 10A. To ensure a robust design, the inductor selected should maintain approximately 50% of

its rated inductance during the worst-case peak current from an output short circuit. For a low-side current limit

substituting zero for output voltage in the expression for

characteristics are preferred. One inductor that meets the peak current guidelines is an off-the-shelf 1.0 µH

component that can handle a peak current of 18A and an average current of 14A. The inductor current ripple and

equation for minimum inductance:

(20)

OUTPUT CAPACITOR

The output capacitor in a switching regulator is selected on the basis of capacitance, equivalent series resistance

(ESR), size, and cost. An important specification in switching converters is the output ripple voltage,

kHz the impedance of most capacitors is very small compared to ESR, hence ESR becomes the main selection

guide. In this design the load requires a 1% ripple, which results in a

(21)

capacitors are all popular in switching converters. Generally, by the time enough capacitors have been paralleled

to obtain the desired ESR, the bulk capacitance is more than enough to supply the load current during a transient

from no-load to full load. In this example the load could transition quickly from 0A to 5A, (or from 5A to 0A), so

moderate bulk capacitance is needed. Two MLCC capacitors rated 100 µF, 6.3V each with ESR of 1.5 m

Ω will

work well.

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