Application information

AN1518

18/30

High impedance paths (in particular the feedback connections) are susceptible to

interference, so they should be as far as possible from the high current paths. An layout

example is provided in Figure 13 below.

The input and output loops are minimized to avoid radiation and high frequency resonance

problems. The feedback pin connections to the external divider are very close to the device

to avoid pick-up noise. Another important issue is the groundplane of the board. Since the

package has an exposed pad, it is very important to connect it to an extended groundplane

in order to reduce the thermal resistance junction-to-ambient.

Figure 13.

Layout example

9.3

Thermal considerations

The dissipated power of the device is tied to three different sources:

●

Equation 22

Where D is the duty cycle of the application. Note that the duty cycle is theoretically given by

compensate for the losses in the overall application. For this reason, the switching losses

●

Switching losses due to turning ON and OFF. These are derived using the following

equation:

Equation 23

L5973D

Cin

D

Cout

L

Inhibit signal

to output voltage

Vin

Vout

Gnd

R1

R2

1

4

5

8

VERY SMALL HIGH CURRENT

CIRCULATING PATH TO MINIMIZE

RADIATION AND HIGH FREQUENCY

RESONANCE PROBLEMS

OUTPUT CAPACITOR

DIRECTLY

CONNECTED TO

HEAVY GROUND

COMPENSATION NETWORK FAR

FROM HIGH CURRENT PATHS

MINIMUN SIZE OF FEEDBACK

PIN CONNECTIONS TO AVOID

PICKUP

CONNECTION TO

GROUNDPLANE

THROUGH VIAS

EXTENDED GROUNDPLANE

ON THE BOTTOM SIDE

P

ON

R

DSON

I

OUT

()

•

2

D

•

=

P

SW

V

IN

I

OUT

T

ON

T

OFF

+

()

2

------------------------------------

•

•

F

SW

V

IN

=

•

I

OUT

T

SW

•

F

SW

•

•

=