2003 Mar 20
10
Philips Semiconductors
Objective specification
2
×
25 W class-D power amplifier
TDA8922
8.3.4
S
UPPLY VOLTAGE ALARM
If the supply voltage drops below
±
12.5 V, the
undervoltage protection circuit is activated and the system
will shut down correctly. If the internal clock is used, this
switch-off will be silent and without plop noise. When the
supply voltage rises above the threshold level, the system
is restarted again after 100 ms. If the supply voltage
exceeds
±
32 V the overvoltage protection circuit is
activated and the power stages will shut down. They are
re-enabled as soon as the supply voltage drops below the
threshold level.
An additional balance protection circuit compares the
positive (V
DD
) and the negative (V
SS
) supply voltages and
is triggered if the voltage difference between them
exceeds a certain level. This level depends on the sum of
both supply voltages. An expression for the unbalanced
threshold level is as follows: V
th(unb)
≈
0.15
×
(V
DD
+ V
SS
).
Example: With a symmetrical supply of
±
30 V, the
protection circuit will be triggered if the unbalance exceeds
approximately 9 V; see Section 16.7.
8.4
Differential audio inputs
For a high common mode rejection ratio and a maximum
of flexibility in the application, the audio inputs are fully
differential. By connecting the inputs anti-parallel the
phase of one of the channels can be inverted, so that a
load can be connected between the two output filters.
In this case the system operates as a mono BTL amplifier
and with the same loudspeaker impedance an
approximately four times higher output power can be
obtained.
The input configuration for a mono BTL application is
illustrated in Fig.6; for more information see Chapter 16.
In the stereo single-ended configuration it is also
recommended to connect the two differential inputs in
anti-phase. This has advantages for the current handling
of the power supply at low signal frequencies.
handbook, full pagewidth
Vin
IN1
+
OUT1
power stage
MBL466
OUT2
SGND
IN1
−
IN2
+
IN2
−
Fig.6 Input configuration for mono BTL application.
