Obsolete

Product(s)

- Obsolete

Product(s)

AN1645 - APPLICATION NOTE

19/22

12. BOARD LAYOUT

Any Switch Mode Power Supply requires a good PCB (Printed Circuit Board) design layout in order to

achieve maximum performance in terms of system functionality and emitted radiations. Components

placing, traces routing and width are the major issues.

Some fundamental rules will be given so that the PCB designer can produce a good layout.

All traces carrying current should be drawn on the PCB as short and thick as possible. This should be done

to minimize resistive and inductive parasitic effects, gaining in system efficiency and radiated emissions.

Current return routing is another crucial issue. Signal ground (SGLGND) and power ground (PWRGND)

must be routed separately and connected to a single ground point.

The INHIBIT pin, due to the -25mV comparator could be sensitive to layout, so make the INHIBIT

connection as short as possible.

As a rule of thumb, traces carrying signal currents should be placed far from traces carrying pulsed

currents or quickly swinging voltages avoiding any coupling effect between them.

Figure 21a: Board Layout - Top Components

Pow e r Se ction

Q1- Q5- Q4

For wa rd S y nc hrono us M osfets

Q2- Q3- Q6

Free wh eeli ng S y nc hron ous M osfet

R2, R 3

Gate pull do wn res is tors

D1

A Schottky Rectifier in parallel to fr ee wh eeling m os fet can increase con ve rter

efficienc y

C1, R 1

A s nubbe r re duces fre ew he eling tu rn- o ff s pik e