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
SOLUTION
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.
DVDD
+
AVDD
+
7
6
10
14
DVDD
DGND
AVDD
C1
C2
VREFP
C3
C4
C5
9
AGND
DGND
13
VREFN
AGND
12
VMI
+
C8
C9
AGND
Notes:
1. AGND and DGND should be connected as close to the IC as possible.
2. C, C3, C4 and C should be 0.1µF multi-layer ceramics, positioned as close to the IC as possible.
2
8
3. Capacitor types for C , C , C should be carefully chosen. 10µF capacitors with low ESR are
1
5
9
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:
apps@wolfsonmicro.com
+44 (0)131 272 7070
+44 (0)131 272 7001
Mail:
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
January 2003, Rev 1.0
w
2
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
