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AS3421 AS3422

Datasheet - A p p l i c a t i o n I n f o r m a t i o n

11.3 Layout Recommendation

Whereever you have audio circuits mixed with power management layout of the blocks is a critical issue. The AS3421/22 has an integrated

charge pump which operates at a frequency of 1Mhz. If the layout of the PCB is not done properly the charge pump can directly influence the

audio performance of the device. Therefore it is very important to make sure that the layout of the charge pump is done properly.

The layout recommendation shown in Figure 43 below shows an example placement of the components of the charge pump. The reference

designators of the components used in the example refer to the schematic shown in Figure 37. It can be seen clearly that the ground pins of all

capacitors as well as the ground pin of AS3422 are placed closely. This compact placement of the components help to minimize high frequency

cross over currents all over the PCB and therefore helps to improve the audio quality. A dedicated ground plane on the top (red) layer minimizes

the resistance between the ground pads of the components. The ground plane (GND) is then connected to the analog ground (AGND) at a single

point which is indicated with three vias in the example.

Figure 43. AS3422 CP Layout Recommendation

If the physical alignment of the components allows it, it is also recommended to connect the charge pump ground plane on top layer directly to

the battery ground terminal of your device. The analogue- (AGND) and charge pump ground plane (GND) are then connected together directly at

the battery terminal. This concept is also know as star shaped ground concept shown in Figure 44 below.

Figure 44. AS3422 Star Shaped Ground Concept

IA connection to analog

round plane (AGND)

Charge pump ground (GND) and

analog ground (AGND) are

directly connected together at

negative battery terminal.

AS3422 Datasheet(PDF) 52 Page - ams AG