AN2507 Datasheet, PDF (10/31 Pages) STMicroelectronics – This application note explains the design of a FLASH LED driver using the STCF03 device

PCB design
3
PCB design
AN2507
3.1
PCB design rules
STCF03 is a powerful switching device where the PCB must be designed in line with
switched supplies design rules. The power tracks (or wires in demo-board) must be as short
as possible and wide enough, because of the high currents involved. It is recommended to
use a 4 layers PCB to get the best performance. All external components must be placed as
close as possible to STCF03. All high-energy switched loops should be as small as possible
to reduce EMI. Most of LEDs need efficient cooling, which could be done by using a
dedicated copper area on the PCB. Please refer to the selected LED's reference guide to
design the heatsink. Place the R_FL resistor as close as possible to the PGND pins and the
ground pin of the COUT capacitor. In case a modification of any PCB layer is required, it is
highly recommended to use enough vias. Place the NTC resistor as close as possible to the
LED for good temperature sensing. Direct connection between GND and PGND is
necessary in order to achieve correct output current value. No LED current should flow
through this track! Voltage sensing on the R_FL resistor must to done on a track from ball FB2
and directly connected to the R_FL resistor. Again, no current should flow through this track.
Pin FB2S must be connected to the R_FL resistor pin. Vias connecting the STCF03 pins to
the copper tracks (if used) must be 0.1 mm in diameter for BGA version. It is recommended
to use the filled vias.
3.2
3.2.1
PCB layout
A four-layer PCB with application area 45.1 mm² for BGA package,
version B
(for version C is layout exactly same except the NTC connection, see Figure 1)
Figure 3. Top layer
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