PAM2400 datasheet(11/14 Pages) PAM

11 / 14 page

Application Information

12/2007 Rev 1.0

Power Analog Microelectronics Inc

www.poweranalog.com

Inductor Selection

Output and Input Capacitor Selection

Input Capacitor

Output Capacitor

Component Power Dissipation

PC Board Layout considerations

To select an inductor for PAM2400 applications,

it should be noted that the inductors current

saturation rating should be larger than the

possible peak inductor current to ensure proper

operation, and it should have low DCR (DC

resistance). Using an inductor with the saturation

current lower than the possible peak indicator

current can cause a dramatic drop in the

inductance and

decay the maximum

output current levels. An inductor is chosen

based on desired ripple current. Larger

inductors result in lower ripple currents, and

smaller ones higher ripple. A 100uH inductor will

be a s uitable choice f or most PAM2400

applications. The following equation can also

help to get a good approximate value for the

inductor.

L=V *D

Duty Cycle) 1 V

(Ripple Current) in the Inductor, i.e., 20% to

40% of the maximum inductor current(Ip).

F (Switching Frequency)=100K.

An input capacitor of minimum 22 F i s

recommended to reduce input ripple and

switching noise for normal operating conditions.

A larger capacitor with lower ESR (Equivalent

Series Resistance) may be needed if the

application requires very low input ripple.

Usually ceramic capacitors are a good choice for

applications. Note that the input capacitor should

be located as close as possible to the IC.

A m inimum

output

capacitor

recommended and may-be a larger one is better.

The t otal output voltage ripple has two

components, the capacitive ripple caused by the

charging and discharging on the output

capacitor, and the ohmic ripple due to the

capacitor's equivalent series resistance (ESR):

V=V

1 2LC

And V

Where Ipeak is the peak inductor current

Multilayer ceramic capacitors are a good choice

as they have extremely low ESR and are

available in small footprints. Capacitance and

ESR variation v s t emperature s hould b e

considered for best performance in applications

with wide operating temperature ranges.

Operating in discontinuous mode, power loss in

the winding resistance o f t he inductor i s

approximately equal to

PDL=2/3(T /L)*R *((V

+V )/V

)*P

The power dissipated in a switch loss is

PDsw=2/3(T /L)*R *((V

+V -V )/V

)*(P

)

The power disspated in rectifier diode(Internal

Diode) is

PDd=V *I

Where P

, R =Inductor DCR,

V =Diode drop

Careful PC board layout is important for

minimizing ground bounce and noise. Keep the

IC's GND pin and the ground leads of input and

output capacitors as close as possible. In

addition, connect L1 and SW with short and wide

connections.

severely

NOUT

RIPPLE

RIPPLE(C)

RIPPLE(ESR)

RIPPLE(C

OUT

OUT MAX

IN MIN

PEAK

OUT

RIPPLE ESR

PEAK

ESR COUT

OUT

DOUT

OUT

O UT

OUT

/(△ * )

/ *( /(

*((

))))

)

(

ΔI

)(

)

(

)

(

)

()

(

)

≈

PAM2400

3-Pin Synchronous Step-Up DC/DC Converter

PAM2400 Datasheet(PDF) 11 Page - Power Analog Micoelectronics

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