CS47L35 datasheet(145/300 Pages) CIRRUS

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DS1085F3

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CS47L35

4.11 Output Signal Path

The speaker driver signal paths incorporate a boost function that shifts the signal levels between the AVDD and SPKVDD

voltage domains. The boost is preconfigured (+12 dB) for the recommended AVDD and SPKVDD operating voltages (see

Table 3-3).

Ultralow leakage and high PSRR allow the speaker supply SPKVDD to be connected directly to a lithium battery.

Note that SYSCLK must be present and enabled when using the Class D speaker output; see Section 4.16 for details of

SYSCLK and the associated control fields.

The OUT4L output signal path is associated with the analog outputs SPKOUTP and SPKOUTN.

The Class D speaker output is a pulse-width modulated signal, and requires external filtering in order to recreate the audio

signal. With a suitable choice of external speakers, the speakers themselves can provide the necessary filtering. See

Section 5 for further information on Class D speaker connections.

The external speaker connection is shown in Fig. 4-51, assuming a suitable speaker is chosen to provide the PWM

filtering.

Figure 4-51. Speaker Connection

The speaker output path is designed to support monitoring of external loudspeakers, giving real-time feedback for

algorithms such as Cirrus Logic’s speaker protection software. Specific external connections are necessary when using

this feature, as detailed below.

The Speaker Protection software, implemented on one of the integrated DSP cores, enables loudspeakers to be protected

from excessive signal levels and other electro-mechanical constraints. The monitoring circuit enables the operational limits

to be continually optimized for the particular loudspeaker and the prevailing conditions. Factors such as cone excursion,

resonance, and thermal behavior of the loudspeaker are modeled in the Speaker Protection software. As a result, the

maximum audio output can be achieved, while ensuring the loudspeakers are also fully protected from damage.

Separate P/N ground connections are provided for the speaker driver; these pins relate to the positive/negative output

transistors respectively, to allow comprehensive current monitoring in the output paths, as an input to the speaker

protection algorithms.

The external speaker connections, incorporating the output current monitoring requirements, are shown in Fig. 4-52. Note

that, if output current monitoring is not required, these connections should be tied directly to ground on the PCB.

SPKOUTP

SPKOUTN

CS47L35

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