NB650/NB650H – 6A, 28V, FAST TRANSIENT SYNCHRONOUS STEP-DOWN CONVERTER

NB650/NB650H Rev. 1.1

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16

10/11/2012

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ramp is not needed. A minimum ESR value of

12mΩ is required to ensure stable operation of

the converter. For simplification, the output ripple

can be approximated as:

OUT

OUT

OUT

ESR

SW

IN

VV

V(1

) R

fL

V

Δ=

× −

×

×

(32)

Inductor

The inductor supplies constant current to the

output load while being driven by the switching

input voltage. A larger value inductor results in

less ripple current, which results in lower output

ripple voltage. However, a larger value inductor is

physically larger, has a higher series resistance,

and/or lower saturation current. To determine the

inductor value, allow the inductor peak-to-peak

ripple current to reach approximately 30% to 40%

of the maximum switch current limit. Make sure

that the peak inductor current is below the

maximum switch current limit. The inductance

value can be calculated as:

OUT

OUT

SW

L

IN

VV

L(1

)

fI

V

=× −

×Δ

(33)

rent.

Choose an inductor that will not saturate under

the maximum inductor peak current. The peak

inductor current can be calculated as:

OUT

OUT

LP

OUT

SW

IN

VV

II

(1

)

2f

L

V

=+

× −

×

(34)