AN726 データシートの表示（PDF） - Silicon Laboratories

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AN726

UTILITY CLASS-D TOOLSTICK USER’S GUIDE

Silicon Laboratories 

AN726

5.3. EPCA0 Class-D Output

In all modes, the EPCA0 module runs in center-aligned PWM mode with an upper limit of 256. This means that the

channels operate in the range of 0–511, since the channels count in half clocks. When the positive channel is on

longer than the negative channel, the resulting equivalent energy is positive (above zero). When the negative

channel is on longer than the positive channel, the resulting equivalent energy is negative (below zero). Combined

with the components on the output, this PWM scheme generates the output waveform on the speaker as shown in

Figure 9.

PB4.0 (R+)

FB

L

Cg

C

PB4.1 (R-)

FB

L

Cg

CH0 (R+)

CH1 (R-)

Differential

Figure 9. Class-D Output Example

Note: The output network configuration in Figure 9 is the configuration in Revision 1.0 of the hardware. An alternate output net-

work discussed in 6. "Tuning the Class-D Output Network‚" on page 18 may provide better performance than the original

configuration.

5.4. Volume Control

The volume control on the Class-D ToolStick board uses the current-limiting feature of the high drive I/O to adjust

the output power. This has the additional benefit of allowing the PWM to always operate at full range, even at lower

volumes, which reduces firmware size and improves sound quality.

Rev. 0.1

11

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