UCC28950_13 Datasheet, PDF (1/11 Pages) Texas Instruments – Frequency Dithering With the UCC28950 and TLV3201

Application Report
SLUA646 – May 2012
Frequency Dithering With the UCC28950 and TLV3201
John Stevens
High Performance Isolated Power
ABSTRACT
For some power-supplies, even after careful considerations throughout the design cycle
the issue of Electro-Magnetic Compatibility (EMC) still remains. One final tool available to
power designers is the use of Frequency Dithering to pass EMC compliance testing. This
paper demonstrates a simple circuit that could be used when such a need arises.
Contents
Abstract....................................................................................................................................................1
Introduction .............................................................................................................................................2
Background .............................................................................................................................................2
Example Using a small UCC28950 Control Card .................................................................................3
Original Circuit...................................................................................................................................3
Calculations.......................................................................................................................................4
Dither Circuit Simulation....................................................................................................................5
Dither Circuit Hardware .....................................................................................................................6
Conclusions.............................................................................................................................................9
Appendix..................................................................................................................................................9
References.............................................................................................................................................10
Figures
Figure 1. Typical Dither Application Circuit with UCC28950 and TLV3201...................................2
Figure 2. Two Output Signals of the UCC28950 without dithering added ....................................3
Figure 3. TLV3201 Comparator Frequency-Dither Circuit in SPICE simulator .............................5
Figure 4. Performance of Comparator Circuit in Simulation..........................................................6
Figure 5. Hardware-tested output of Comparator Board ................................................................7
Figure 6. Two Output Signals of the UCC28950 with dithering added ..........................................7
Figure 7. Two Output Signals of the UCC28950 with dithering added (single capture =
122kHz) ................................................................................................................................8
Figure 8. Two Output Signals of the UCC28950 with dithering added (single capture =
144kHz) ................................................................................................................................8
Figure App 1. UCC28950 Small Control Card Schematic ................................................................9
Figure App 2. UCC28950 Small Control Card Layout and Assembly .............................................9
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