Application information

A6727

22/29

DocID025003 Rev 1

10

Application information

10.1

Output inductor

The inductor value is defined by a compromise among the dynamic response, ripple,

efficiency, cost and size. Usually, the inductance is calculated to maintain the inductor ripple

current (

Equation 8

Figure 12 shows the ripple current vs. the output voltage for different inductance, with

Increasing the value of the inductance, the inductor ripple current (and output voltage ripple

accordingly) reduces but, at the same time, the converter response time to load transients

increases. Higher inductance means that the inductor needs more time to change its current

from initial to final value. Until the inductor has finished its charging, the additional output

current is supplied by the output capacitors. Minimizing the response time, the required

output capacitance can be minimized. If the compensation network is designed with high

bandwidth, during a load transient the device can saturate duty cycle (0% or 80%). When

this condition is reached, the response time is limited only by the time required to charge the

inductor.

Figure 12. Inductor current ripple vs. output voltage

L

V

IN

V

OUT

–

F

SW

ΔI

L

⋅

------------------------------

V

OUT

V

IN

--------------

⋅

=

0

2

4

6

8

10

012345

Output voltage [V]

Vin=12 V, L=1 uH

Vin=12 V, L=2 uH

Vin=5 V, L=500 nH

Vin=5 V, L=1.5 uH

AM16776v1