CS47L35 datasheet(232/300 Pages) CIRRUS

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232

DS1085F3

CS47L35

5.1 Recommended External Components

Figure 5-6. ESD Diode Configuration for External Output Connections

5.1.5

Speaker-Driver Output Path

The CS47L35 incorporates a Class D speaker driver, offering high amplifier efficiency at large signal levels. As the Class D

output is a pulse-width modulated signal, the choice of speakers and tracking of signals is critical for ensuring good

performance and reducing EMI in this mode.

The efficiency of the speaker driver is affected by the series resistance between the CS47L35 and the speaker (e.g., PCB

track loss and inductor ESR) as shown in Fig. 5-7. This resistance should be as low as possible to maximize efficiency.

Figure 5-7. Speaker Connection Losses

The Class D output requires external filtering to recreate the audio signal. This may be implemented using a 2nd order LC

or 1st order RC filter, or else may be achieved by using a loudspeaker whose internal inductance provides the required

filter response. An LC or RC filter should be used if the loudspeaker characteristics are unknown or unsuitable, or if the

length of the loudspeaker connection is likely to lead to EMI problems.

In applications where it is necessary to provide Class D filter components, a second-order LC filter is the recommended

solution as it provides more attenuation at higher frequencies and minimizes power dissipated in the filter when compared

to a first order RC filter (lower ESR). This maximizes both rejection of unwanted switching frequencies and overall speaker

efficiency. A suitable implementation is shown in Fig. 5-8.

HPOUTL

HPOUTR

External Headphone/Line

Output Connection

External Headphone/Line

Output Connection

ESD Protection Diodes

CS47L35

GND

Switching

Losses

Class D

output

SPKVDD

SPKVDD/2

Losses due to resistance between output driver and

speaker (e.g., inductor ESR). This resistance must be

minimised in order to maximise efficiency .

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