www.ti.com

Peak Current Rating of Inductor

I

V

OUT

C

OUT

T

SS

(9)

L

1

2

I

I

CHARGE

(10)

Input Capacitor Selection (C1 & C2)

C

I

LOAD

V

OUT

V

RIPPLE(cap)

V

IN

F

SW

(11)

ESR

V

RIPPLE(ESR)

I

LOAD

1

2

I

(12)

I

I

I

1

12

I

RIPPLE

V

OUT

V

IN

V

OUT

I

OUT

V

IN

(13)

TPS40040, TPS40041

SLUS700B – MARCH 2006 – REVISED MARCH 2006

With output capacitance known, it is now possible to calculate the charging current during start-up and determine

the minimum saturation current rating for the inductor. The start-up charging current is approximated by:

mA. The peak current rating of the inductor is now found by:

The inductor requirements are summarized in the table below.

Inductor Requirements

PARAMETER

SYMBOL

VALUE

UNITS

Inductance

L

1.0

µH

RMS current (thermal rating)

6.15

A

Peak current (saturation rating)

7.08

A PG0083.102, 1.0

µH is selected for its small size, low DCR and high current handling capability.

ceramic capacitors with about 5-m

Ω ESR and a 2-A RMS current rating are selected. It is important to check the

dc bias voltage derating curves to ensure the capacitors provide sufficient capacitance at the working voltage.

21