Philips Semiconductors
Controller class-D audio amplifier
Preliminary specification
TDA8929T
15 TEST AND APPLICATION INFORMATION
15.1 Test circuit
The test diagram in Fig.10 can be used for stand alone
testing of the controller. Audio and mode input pins are
configured as in the application. For the simulation of a
switching output power stage a simple level shifter can be
used. It converts the digital PWM signal from the controller
(switching between VSS and VSS + 12 V level) to a
PWM signal switching between VDD and VSS.
A proposal for a simple level shifting circuit is given
in Fig.9.
The low-pass filter performs the demodulation, so that the
audio signal can be measured with an audio analyzer. For
measuring low distortion values, the speed of the level
shifter is important. Special care has to be taken at a
sufficient supply decoupling and output waveforms without
ringing.
The handshake with the power stage is simulated by a
direct connection of the release inputs (REL1 and REL2)
with the switch outputs (SW1 and SW2) of the controller.
The enable outputs (EN1 and EN2) for waking-up the
power stage are not used here, only the output level and
timing are measured.
handbook, full pagewidth
switch
0/12 V
VSS
2 kΩ
+5 V
20 kΩ
10 kΩ
BST82
1.33 kΩ
74LV14
10 Ω
PHC2300
10 nF
10 Ω
33 Ω
42 Ω
VDD
PWM
MGW154
VSS
Fig.9 Level shifter.
2001 Dec 11
17