CS43L36 datasheet(26/89 Pages) CIRRUS

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DS1081F3

CS43L36

4.3 Class H Amplifier

Figure 4-7. VCP_FILT Hysteresis—Headphone Output

4.3.3

Efficiency

As discussed in previous sections, amplifiers internal to the CS43L36 operate from one of four sets of rail voltages, based

on the needs of the signal being amplified. Fig. 4-8 and Fig. 4-9 show power curves for all modes of operation and provides

details regarding the power supplied to 15- and 30-

stereo loads versus the power drawn from the supply for each

Class H mode.

If rail voltages are set to ±2.5 V, the amplifiers operate in their least efficient mode for low-level signals. If they are held at

±VCP, ±VCP/2, or ±VCP/3, amplifiers operate more efficiently, but are clipped if required to amplify a full-scale signal.

The adapt-to-signal trace shows the benefit of four-mode Class H operation. At lower output levels, amplifier output is

represented by the ±VCP/3 or ±VCP/2 curve, depending on the signal level. At higher output levels, amplifier output is

represented by the ±VCP or ±2.5-V curve. The duration for which the amplifiers operate within any of the four curves

(±VCP/3, ±VCP/2, ±VCP, or ±2.5 V) depends on both the content and the output level of the material being amplified. The

highest efficiency operation results from maintaining an output level that is close to, without exceeding, the clip threshold

of the particular supply curve.

Note that the Adapt-to-Signal Mode trace in Fig. 4-8 shows that it never transitions to Mode 0, because FULL_SCALE_

VOL = 1 (–6 dB) due to a 15-

 stereo load.

Output Level

–14 dB

+VCP

5.5 s

Amplifier Rail

Voltage

Time

+VCP

5.5 s

–VCP

–10 dB

5.5 s

–4 dB

+2.5 V

–2.5 V

–4.5 dB

–10.5 dB

–14.5 dB

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