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WAN-0129

Decoupling and Layout Methodology for Wolfson DACs, ADCs and CODECs

Wolfson Microelectronics plc 

WAN_0129

ANALOGUE SUPPLY

Analogue supply pins must be connected to a low-noise analogue supply rail, which ideally comes

from a low-noise linear regulator. We name these pins like this: AVDD, HPVDD, SPKVDD. Be sure

to place a 0.1µF multi-layer ceramic capacitor close to each of these pins (within 3mm) to decouple it

properly to AGND. If there is no large-value capacitor within 50mm, then also add one 10µF low-

ESR capacitor per rail. This can be multi-layer ceramic, low-ESR tantalum or low-ESR organic

semiconductor electrolytic type. Check the datasheet shows the part has less than 200mΩ ESR for

best performance.

On some of our devices there are internal supplies or references which require external decoupling.

We names these pins like: VMID, VREF, VREFOUT, CAP2. The pins connect just to a capacitor,

not to an external supply. Be sure to place a 0.1µF multi-layer ceramic capacitor close to each of

these pins (within 3mm) to decouple it properly to AGND. Also add one 10µF low-ESR capacitor per

pin. This can be multi-layer ceramic, low-ESR tantalum or low-ESR organic semiconductor

electrolytic type. Check the datasheet shows the part has less than 200mΩ ESR for best

performance.

SUPPLY LAYOUT

Ideally the supply connections will be made with planes on a multi-layer circuit board. If these planes

are on adjacent layers, the parasitic capacitance of these layers will further improve high-frequency

decoupling. Where this is not possible, use tracks much wider than the current rating requires.

SOLUTION

DVDD

+

C1

C2

DGND

7 DVDD

6 DGND

AVDD 10

AVDD

VREFP 14

+

C3

C4

C5

AGND 9

VREFN 13

AGND

VMI 12

C8

+

C9

AGND

Notes:

1. AGND and DGND should be connected as close to the IC as possible.

2. C2, C3, C4 and C8 should be 0.1µF multi-layer ceramics, positioned as close to the IC as possible.

3. Capacitor types for C1, C5, C9 should be carefully chosen. 10µF capacitors with low ESR are

recommended for optimum performance.

Figure 2 Decoupling Example

CONCLUSION

With careful consideration of layout and provision of low-noise supplies, the performance specified in

our datasheets should be achieved.

APPLICATION SUPPORT

If you require more information or require technical support please contact Wolfson Microelectronics

Applications group through the following channels:

Email:

Telephone:

Fax:

Mail:

apps@wolfsonmicro.com

+44 (0)131 272 7070

+44 (0)131 272 7001

Applications at the address on last page.

or contact your local Wolfson representative.

Additional information may be made available from time to time on our web site at

http://www.wolfsonmicro.com

w

January 2003, Rev 1.0

2

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