2003 Mar 20
7
Philips Semiconductors
Objective specification
2
×
25 W class-D power amplifier
TDA8922
8
FUNCTIONAL DESCRIPTION
8.1
General
The TDA8922 is a two channel audio power amplifier using
class-D technology. A detailed application reference
design is shown in Fig.10. Typical application schematics
are shown in Figs 37 and 38.
The audio input signal is converted into a digital Pulse
Width Modulated (PWM) signal via an analog input stage
and PWM modulator. To enable the output power
transistors to be driven, this digital PWM signal is applied
to a control and handshake block and driver circuits for
both the high side and low side. In this way a level shift is
performed from the low power digital PWM signal
(at logic levels) to a high power PWM signal which
switches between the main supply lines.
A 2nd-order low-pass filter converts the PWM signal to an
analog audio signal across the loudspeakers.
The TDA8922 one-chip class-D amplifier contains high
power D-MOS switches, drivers, timing and handshaking
between the power switches and some control logic. For
protection a temperature sensor and a maximum current
detector are built-in.
The two audio channels of the TDA8922 contain two
PWMs, two analog feedback loops and two differential
input stages. It also contains circuits common to both
channels such as the oscillator, all reference sources, the
mode functionality and a digital timing manager.
The TDA8922 contains two independent amplifier
channels with high output power, high efficiency (90%),
low distortion and a low quiescent current. The amplifier
channels can be connected in the following configurations:
•
Mono Bridge-Tied Load (BTL) amplifier
•
Stereo Single-Ended (SE) amplifiers.
The amplifier system can be switched in three operating
modes with pin MODE:
•
Standby mode; with a very low supply current
•
Mute mode; the amplifiers are operational, but the audio
signal at the output is suppressed
•
Operating mode; the amplifiers fully are operational with
output signal.
An example of a switching circuit for driving pin MODE is
illustrated in Fig.4.
For suppressing plop noise, the amplifier will remain
automatically in the mute mode for approximately 150 ms
before switching to the operating mode (see Fig.5).
During this time, the coupling capacitors at the input are
fully charged.
handbook, halfpage
standby/
mute
R
R
mute/on
MODE pin
SGND
MBL463
+
5 V
Fig.4 Example of mode selection circuit.
