WM9093ECSSLASHR datasheet(80/84 Pages) WOLFSON

80 / 84 page

WM9093

Production Data

PD, March 2012, Rev 4.2

For filterless Class D operation, it is important to ensure that a speaker with suitable inductance is

chosen. For example, if we know the speaker impedance is 8Ω and the desired cut-off frequency is

20kHz, then the optimum speaker inductance may be calculated as:

 loudspeakers typically have an inductance in the range 20H to 100H, however, it should be

noted that a loudspeaker inductance will not be constant across the relevant frequencies for Class D

operation (up to and beyond the Class D switching frequency). Care should be taken to ensure that

the cut-off frequency of the loudspeaker’s filtering is low enough to suppress the high frequency

energy of the Class D switching and, in so doing, to prevent speaker damage. The Class D outputs of

the WM9093 operate at much higher frequencies than is recommended for most speakers and it must

be ensured that the cut-off frequency is low enough to protect the speaker.

RECOMMENDED EXTERNAL COMPONENTS DIAGRAM

Figure 20 below provides a summary of recommended external components for WM9093. Note that

the diagram does not include any components that are specific to the end application e.g. they do not

include filtering on the speaker outputs (assume filterless class D operation), RF decoupling, or RF

filtering for pins which connect to the external world i.e. headphone or speaker outputs.

Figure 20 Recommended External Components

WM9093ECS/R データシート(PDF) 80 Page - Wolfson Microelectronics plc