AN2620 Datasheet, PDF (16/20 Pages) STMicroelectronics – 3 A high-frequency synchronous 900 kHz

Board usage recommendation
AN2620
4.6
Layout considerations
The layout is an important step in the design for all switching power supplies.
The high-speed operation (900 kHz) of the ST1S10 device demands careful attention to the
PCB layout. Care must be taken in the board layout to obtain maximum device performance,
otherwise the regulator could show poor line and load regulation, stability issues as well as
EMI problems.
It is critical to provide a low inductance, impedance ground path. Therefore, use wide and
short traces for the main current paths.
The input capacitor must be placed as close as possible to the IC pins as well as the
inductor and output capacitor. Use a common ground node for power ground and a different
one for control ground (AGND) to minimize the effects of ground noise. Connect these
ground nodes together underneath the device and make sure that small signal components
returning to the AGND pin do not share the high current path of C_IN and C_OUT.
The feedback voltage sense line (V_FB) should be connected right to the output capacitor and
routed away from noisy components and traces (e.g., SW line). Its trace should be
minimized and shielded by a guard-ring connected to the ground.
Figure 12. PCB layout suggestion
V_FB guard-ring
Output Voltage
Enable/
Disable
Input Sync
Input capacitor C1 must be placed
as close as possible to the IC
pins as well as the inductor L1
and Output capacitor C2
Input Power Supply
Via holes from thermal pad
To bottom layer
16/20
Doc ID 13883 Rev 3