CS47L85 datasheet(204/370 Pages) CIRRUS

204 / 370 page

CS47L85

204

Rev 4.3

OUTPUT SIGNAL PATH

The CS47L85 provides six stereo pairs of audio output signal paths. These outputs comprise ground-referenced headphone

drivers, differential speaker drivers and digital output interfaces suitable for external speaker drivers. The output signal paths

are summarised in Table 70.

SIGNAL PATH

DESCRIPTIONS

OUTPUT PINS

OUT1L, OUT1R

Ground-referenced headphone output

HPOUT1L, HPOUT1R

OUT2L, OUT2R

Ground-referenced headphone output

HPOUT2L, HPOUT2R

OUT3L, OUT3R

Ground-referenced headphone output

HPOUT3L, HPOUT3R

OUT4L, OUT4R

Differential speaker output

SPKOUTLN, SPKOUTLP,

SPKOUTRP, SPKOUTRN

OUT5L, OUT5R

Digital speaker (PDM) output

SPKDAT1, SPKCLK1

OUT6L, OUT6R

Digital speaker (PDM) output

SPKDAT2, SPKCLK2

Table 70 Output Signal Path Summary

The analogue output paths incorporate high performance 24-bit sigma-delta DACs.

Under default conditions, the headphone drivers provide a stereo, single-ended output. A mono mode is also available on

each headphone output pair, providing a differential (BTL) configuration. The ground-referenced headphone output paths

incorporate a common mode feedback path for rejection of system-related noise. These outputs support direct connection

to headphone loads, with no requirement for AC coupling capacitors.

The speaker output paths are configured to drive a stereo pair of differential (BTL) outputs. The Class D design offers high

efficiency at large signal levels. With a suitable choice of external speaker, the Class D output can drive loudspeakers

directly, without any additional filter components.

The digital output paths provide two stereo Pulse Density Modulation (PDM) output interfaces, for connection to external

audio devices. A total of four digital output channels are provided.

Digital filters can be enabled in the output signal paths, supporting audiophile-quality DAC playback options. These Hi-Fi

filters allow user selection of the preferred characteristics, e.g., linear phase, anti-aliasing or apodizing filter responses.

Digital volume control is available on all outputs (analogue and digital), with programmable ramp control for smooth, glitch-

free operation. A configurable noise gate function is available on each of the output signal paths. Any two of the output signal

paths may be selected as input to the Acoustic Echo Cancellation (AEC) loopback paths.

The CS47L85 incorporates thermal protection functions, and provides short-circuit detection on the Class D speaker and

headphone output paths. The General Purpose Timers (see “DSP Peripheral Control”) can also be used as a Watchdog

function, to trigger a shutdown of the Class D speaker drivers.

For further details, refer to the “Thermal Shutdown and Short

Circuit Protection

” section.

The Class D speaker outputs are designed to support monitoring of external loudspeakers, giving real-time feedback for

algorithms such as Cirrus Logic

’s Speaker Protection software, running on one of the DSP cores. This enables loudspeakers

to be protected against damage from excessive signal levels and other electro-mechanical constraints. This feature requires

additional external component connections, as described later in this document.

The CS47L85 output signal paths are illustrated in Figure 60.

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