L3380

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

6 of 9

www.unisonic.com.tw

QW-R502-099,A

APPLICATION CIRCUIT INFORMATION

The following equations show the relation of the basic design parameters.

1. Refer to the application circuit, the increasing inductor current when the switch is turn on is given by the following

equation

11

()

LL ON

IN

S

d

iU T

U

U

LL

f

+

∆=

=

−

(

IN

S

The decreasing inductor current when the switch is turn off can derive by the equation below

11

1

()

LL OFF

O

D

IN

d

iU T

U

U

U

LL

f

−

−

∆=

= −

+

−

（

D

according to

0

LL

ii

+−

∆+ ∆

OD

IN

OD

S

UU

U

d

UU

U

+−

=

+−

2. The average current flowing through the inductor is

1

O

L

I

I

d

=

−

3. We note that

(1

)

OL

I

dI

=−

then we can write:

(1

)

L

OL

L

I

I

di

i

=−

• ∆

∆

substituting

1

LL OFF

iU T

L

∆=

L

i

11

(1

)

OL OFF

I

dU T

ICR L

=−

•

•

(

L

L

i

I

∆

)

11

1

(1

)

(

)

OD

IN

d

Id

Uo U

U

ICR L

f

−

=−

•

•

+

−

derive that

L =

(1– d)

ICR

4. The peak current of the inductor is given by

1

2

PKL

L

I

Ii

=+ ∆

1

2

L

PKL

L

L

i

I

II

I

∆

=+

•

according to

L

L

i

I

∆

derive that

1

2

PKL

L

I

IICR I

=+

•

Then derive the following equation for peak current of inductor

1

(1

)

2

PK

L

I

IICR

=+