WM8786

Production Data

w

PD Rev 4.2 February 2007

22

RECOMMENDED PCB LAYOUT

The WM8786 is sensitive to the routing of the ground return currents for VREF, VMID and AVDD and

care should be taken to ensure that these currents do not interfere.

Figure 25 below shows a

recommended PCB layout (with high frequency current paths) for the WM8786 that will demonstrate

datasheet performance:

C1

C6

C3

C5

C4

Top Layer Copper

Bottom Layer Copper

Via

To AVDD

Supply

C2

To DVDD

Supply

+

+

Figure 25 Recommended PCB Layout for VREF, VMID, AVDD and DVDD Decoupling

Notes:

1.

High frequency noise on VREF is decoupled through C5, and the return path should be directly

to VREFGND.

2.

The route from the negative terminal of C6 to C5 and then to VREFGND should be made on

the top layer only and should not connect to the ground flood on the top layer. This ensures

that the VREF return current is returned directly to VREFGND as shown by the black arrows.

3.

The negative terminal of C6 should be connected to the ground plane on the underside of the

board only.

4.

High frequency noise on VMID is decoupled through C4, and the return path should be directly

to AGND.

5.

Via to bottom layer on VMID used to connect to bottom layer route to positive terminal of C3.

6.

The route from C4 to AGND should be made on the top layer only. This ensures that the VMID

return current is returned to AGND as shown by the white arrows.

7.

AVDD is decoupled to AGND through C1. The ground return currents are not shown in this

diagram.

8.

DVDD is decoupled to DGND through C2. The ground return currents are not shown in this

diagram.

9.

DGND should not be connected directly to the ground flood on the top layer under the

WM8786. This will ensure that noise in the digital ground does not interfere with the critical

routing of VREF and VMID.

10. Bottom layer ground flood not shown for clarity.

11. See the WM8786 Evaluation Board for an example of this layout in use.