AN2507 datasheet(10/31 Pages) STMICROELECTRONICS

10 / 31 page

PCB design

AN2507

10/31

PCB design

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 RFL 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 RFL resistor must to done on a track from ball FB2

and directly connected to the RFL resistor. Again, no current should flow through this track.

Pin FB2S must be connected to the RFL 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

PCB layout

3.2.1

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

AN2507 Datasheet(PDF) 10 Page - STMicroelectronics