WM8983
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SPEAKER BOOST MODE
To support speaker boost mode, AVDD2 should be at least 1.5*AVDD1. A higher AVDD2 will
improve THD performance at the expense of power consumption while lower AVDD2 will cause
clipping.
Variations in AVDD1 and AVDD2 should be taken into account when using speaker boost mode as
shown in Figure 26 and Figure 27.
Figure 26 Non-Boost Mode Output Operation
Figure 27 Boost Mode Output Operation
LOUT2 and ROUT2 outputs can be connected directly to a Lithium battery to improve THD
performance in non-boost mode.
Although direct battery connection is also possible in boost mode, the discharge characteristic of the
battery can lead to clipping after a relatively short period of time as shown in Figure 28. Reducing the
maximum permitted volume and keeping AVDD1 to a minimum will allow boost mode to operate for
longer.
Figure 28 Output Boost Mode with Direct Battery Connection
As the full scale output falls close to AVDD1, it becomes more effective to use non-boost mode to
generate a louder output, although SPKBOOST should NOT be changed while the speaker output is
driving out a signal. As a general rule:
if AVDD2 - (AVDD1 * 0.75) > AVDD1 / 2 boost mode provides more power output;
if AVDD2 - (AVDD1 * 0.75) < AVDD1 / 2 non-boost mode provides more power output.
PP Rev 1.1 August 2005
52
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
