L = 82
H
m
C
= 47
F
C
m
C = 1
F
m
Rload = 32
W
Analog Audio I/O
Because the output signal is a pulse train switching between Power Supply and Ground, the efficiency of
the amplifier is greatly improved. In this mode however, for good noise performance, care should be taken
to keep the analog power supply clean.
For using the Class-D mode of operation, the following clock-divider condition should be met:
MDAC = I × 4, where I = 1, 2, ..., 32
When a direct digital pulse train is driven out as a signal, high frequencies as a function of pulse train
frequency are also present which lead to power waste. To increase the efficiency and reduce power
dissipation in the load due to these high frequencies, an LC filter should be used in series with the output
and the load. The cutoff frequency of the LC filter should be adjusted to allow audio signals below 20kHz
to pass through, but highly attenuate the high-frequency signal content.
Figure 2-5. Configuration for Using Headphone Amplifier in Class-D Mode
For using the headphones in the Class-D mode of operation, the headphones should first be powered up
in default Class-AB mode to charge the AC-coupling capacitor to the set common mode voltage. Once the
headphone amplifiers have been so powered up, the DAC should be routed to headphones and unmuted
before they can be switched to the Class-D mode. After Class D mode has been turned on, the linear,
Class AB mode amplifier must be turned off. For powering down the headphone amplifiers, the DAC
should first be muted.
See
for an example setup script enabling Class-D mode.
20
TLV320DAC3203 Application
SLAU434 – May 2012
Copyright © 2012, Texas Instruments Incorporated