WM8994 datasheet(138/359 Pages) WOLFSON

138 / 359 page

WM8994

Production Data

PD, April 2012, Rev 4.4

138

Eight levels of AC signal boost are provided in order to deliver maximum output power for many

commonly-used SPKVDD/AVDD1 combinations. (Note that SPKVDD1 powers the Left Speaker

driver, and SPKVDD2 powers the Right Speaker driver; it is assumed that SPKVDD1 = SPKVDD2 =

SPKVDD.)

The signal boost options are available in both Class AB and Class D modes. The AC boost levels

from 0dB to +12dB are selected using register bits SPKOUTL_BOOST and SPKOUTR_BOOST. To

prevent pop noise, SPKOUTL_BOOST and SPKOUTR_BOOST should not be modified while the

speaker outputs are enabled. Figure 35 illustrates the speaker outputs and the mixing and gain/boost

options available.

Ultra-low leakage and high PSRR allow the speaker supply SPKVDD to be directly connected to a

lithium battery. Note that an appropriate SPKVDD supply voltage must be provided to prevent

waveform clipping when speaker boost is used.

DC gain is applied automatically in both class AB and class D modes with a shift from VMID to

SPKVDD/2. This provides optimum signal swing for maximum output power. In class AB mode, an

ultra-high PSRR mode is available, in which the DC reference for the speaker driver is fixed at VMID.

This mode is selected by enabling the SPKAB_REF_SEL bit (see Table 74). In this mode, the output

power is limited but the driver will still be capable of driving more than 500mW in 8

 while maintaining

excellent suppression of noise on SPKVDD (for example, TDMA noise in a GSM phone application).

The AC and DC gain functions are illustrated in Figure 35.

Figure 35 Speaker Output Configuration and AC Boost Operation

WM8994 Datasheet(PDF) 138 Page - Wolfson Microelectronics plc