STLDC08

Application information

Doc ID 18476 Rev 1

19/29

Equation 11

Equation 12

Equation 13

following procedure must be performed to choose the Power MOSFET. During ON time, the

SENSE comparator limits the voltage across the Power MOSFET to a nominal 100 mV. In

that case, the maximum inductor current is given by the following relationships:

Equation 14

Equation 15

Equation 16

8.5

Power MOSFET selection

A key parameter to take into account in the selection of the N-MOSFET is the maximum

continuous drain current. As a safety design, it is important to choose a maximum

continuous drain current equal to twice the maximum input current.

)

PK

(

L

)

MAX

(

IN

I

2

I

×

=

2

I

D

1

I

I

L

MAX

LED

)

PK

(

L

Δ

+

−

=

)

PK

(

L

SENSE

I

2

1

.

0

R

×

=

)

ON

(

DS

)

ON

(

DS

SENSE

)

MAX

(

L

R

mV

100

R

V

I

=

=

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

Δ

+

×

−

×

=

×

=

2

I

1

D

1

I

2

I

2

I

L

MAX

LED

)

PK

(

L

)

MAX

(

L

⎟

⎠

⎞

⎜

⎝

⎛

Δ

+

×

×

−

×

<

2

I

1

I

2

D

1

1

.

0

R

L

LED

MAX

)

ON

(

DS