AN1330

Application information

19/31

5.2

Layout considerations

The layout of switching DC-DC converters is very important to minimize noise and

interference. Power-generating portions of the layout are the main cause of noise and so

high switching current loop areas should be kept as small as possible and lead lengths as

short as possible.

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. A 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. Moreover the GND pin of the device is connected to the ground plane

directly with VIA on the bottom side of the PCB.

Figure 13.

Layout example

Coiltronics

UP1B

22 to 33

1 to 1.2

UP2B

33 to 47

1.7 to 2

BI

HM76-2

22 to 33

1 to 1.2

HM76-3

33 to 47

2 to 2.5

Murata

LQN6C

22 to 33

0.9 to 1.2

Panasonic

ELLATV

22 to 47

1.4 to 2.05

Sumida

CR75

22 to 33

1.2 to 1.5

Epcos

B82476

33 to 47

1.6 to 2

Wurth Elektronik

744561

33 to 47

1.6 to 2

Table 4.

Inductor selection (continued)

Manufacturer

Series

Inductor value (

µH)

Saturation current (A)

L5970

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 VIA

AM00012v1