AN_UBA2024T_15 Datasheet, PDF (18/18 Pages) NXP Semiconductors – CFL applications

Philips Semiconductors
CFL applications with the UBA2024T
APPLICATION NOTE
APPENDIX 1 Application board layout example
The layout of the PCB on which the UBA2024T is mounted, has a considerable influence on the performance of the
IC. Issues to be taken into account are:
• Coils with open magnetic circuit should not be placed above the IC (on the other side of the PCB). If an axial
filter inductor is used for LFILT it should be placed in the same direction as the IC to minimize magnetic field
pick-up.
• All output components (CHB1, CHB2, LLA, CLA and CDV) and their interconnections should be placed at the side of
pin 1 and pin 14 of the IC.
• Oscilator pin (pin 7, “RC”) and sweep pin (pin 8, “SW”) should be shielded form output/lamp by a ground track.
Components on these pins should be placed as close to the IC as possible.
• Capacitors CVDD and CFS should be placed close to the IC.
• For effective heat transfer all SGND pins need to be soldered to a copper plane which is also beneath the IC and
extends besides the IC as much as possible. Fixing the IC to the board using thermal conductive glue also helps.
Of course, the size and shape of the PCB has to fit the lamp base. Below the layout of the demoboard, as is used for
the measurements mentioned in this application note, is shown as an example. With it’s diameter of only 35mm it’s
smaller then most currently used CFL-ballast PCBs. It’s suited for either use of the popular E16 core lamp inductor
or a radial-type I-core inductor.
Figure 7: Layout (left) and component placement (right) of application demoboard
(actual size is 35mm diameter)
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