ZXCD1000
Class D 25W Mono Open Loop (Bridge Tied
Load - BTL) Solution
– PCB description and Operation.
The top copper, the bottom copper and the silk screen
(top) are shown in Figures 5, 6 & 7 respectively, for the
double sided PCB implementation of the applications
circuit of Figure 4. A component listing is given in the
BOM (Bill of Materials) table. Gerber files for this
solution are available from Zetex Plc.
The board operates from a 16V (nom.) supply which
should be applied to the underside of the supply
decoupling capacitor C29. The audio input and speaker
connections should be made to the solder pads
indicated on Figure 7. The audio input should have a
maximum amplitude of approximately 1V pk-pk. For
diagnostic purposes, the speaker outputs can be
monitored single-endedly with respect to ground with
an oscilloscope (or other instrument) if desired.
However remember that the speaker is connected as a
Bridge Tied Load, therefore any results obtained in this
manner, are not valid for assessing performance. The
true performance depends upon some differential
cancellation across the speaker load. To view the
differential output across speakerA and speakerB, a
floating monitor must be used i.e. neither side of the
speaker should be grounded! For example, this can be
achieved with a two channel oscilloscope by monitoring
the speakerA and speakerB outputs, and using the invert
and add functions.
Figure 6.
Class D 25W Mono O.L. PCB Bottom Copper (Actual
Size)
The exposed pad on the underside of the ZXCD1000
eQSOP package should be soldered down to the PCB.
This in conjunction with vias and top and bottom
copper areas, functions as a heat sink.
Speaker Outputs
Audio Input
Figure 7.
Class D 25W Mono O.L. PCB
Silk Screen (Actual Size)
Plots of typical performance for the solution are
shown in the included graphs. As previously stated, a
very important feature of the Zetex solution is that the
residual distortion is almost totally free of any
crossover artifacts. This lack of crossover distortion
sets the ZXCD1000 solutions quite apart from most
other presently available low cost solutions, which in
general suffer from severe crossover distortion
problems.
Figure 5.
Class D 25W Mono O.L. PCB Top Copper (Actual Size)
ISSUE 1 - MARCH 2001
8
ETC [ ETC ]
