Cirrus-logic CS42L73 Manuale Utente Scaricare il pdf (Pagina 49)

DS882F1 49

CS42L73

4.5.3 Efficiency

As discussed in previous sections, the HPOUTx and LINEOUTx amplifiers may operate from one of three

pairs of rail voltages based on the amplitude of the output signal or the relevant volume settings in the

signal path. Figure 21 shows total power drawn by the device vs. power delivered to two headphone loads

when the rails are held constant at each of the three available settings, or when the Class H controller is

set to Adapt-to-Volume mode.

Note: Test Conditions: VCP = VL = VA = 1.8 V, VP = 5 V; MCLK = 6 MHz, LRCK = 44.118 kHz; full-scale

input signal applied through HPOUTA and HPOUTB.

If rail voltages are set to ±VCP Mode, the output amplifiers operate in their least-efficient mode for low-lev-

el signals. When rail voltages are held at ±VCP/2 or ±VCP/3, the amplifiers operate in a more efficient

mode, but clip when amplifying a full-scale signal.

The blue trace in Figure 21 shows the benefit of the Tri-Modal Class H design. At lower output levels, the

output of the amplifiers is represented by the ±VCP/3 or ±VCP/2 curves, depending on the signal level.

At higher output levels, the output is represented by the ±VCP curve. The duration in which the amplifiers

operate within any of the three rail pairs (±VCP/3, ±VCP/2, or ±VCP) depends on both the content and

the output level of the program material being amplified. The highest efficiency results from maintaining

an output level that is close to, but does not exceed, the clip threshold of a particular supply curve.

4.6 DAC Limiter

When enabled, the limiter monitors the digital input signal before the DAC modulators, detects when levels

exceed the maximum threshold settings and lowers the volume at a programmable attack rate below the

0.001 0.01 0.1 1 10

Power Delivered to Two 30



Loads (mW)

Power Taken From All Supplies (mW)



VCP/3 Mode



VCP/2 Mode



VCP Mode

Class H Enabled

Figure 21. Input Power vs. Output Power

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Cirrus-logic CS42L73 Manuale Utente Pagina 49