PM6641 datasheet(40/47 Pages) STMICROELECTRONICS

40 / 47 page

Components selection

PM6641

40/47

8.5

Layout guidelines

Each signal is referred to AGND, the analog ground. In a typical 4-layers PCB one internal

layer should be dedicated to this common ground. The IC thermal pad must be connected to

AGND plane through multiple VIAs, in order to remove the IC heat and to obtain the best

performance. Furthermore, each switching regulator has a dedicated power ground

(SGND_1Sxx); all these SGNDs must be star-connected, in a single point, with AGND.

For each switching section the power componets (inductor and input/output capacitors)

must be placed near the VSW_1Sxx, VIN_1Sxx and SGND_1Sxx pins and connected with

large (at least 20mils or larger) and short PCB traces, in order to limit the path of the current

high frequency components and, consequently, to reduce the injected noise. If the power

components routing involves more than one layer, as many VIAs as possible must be

inserted to reduce the series resistance and improve the global efficiency.

The VTT external components (input and output capacitors) must be placed near the LDO

regulator input (LDOIN) and output (VTT) pins, and must be routed with large and short

traces, in order to limit the parasitic series resistance.

The feedback pins (VFB_1Sxx and VTTFB) must reach the feedback points through

dedicated PCB traces, typically 10mils width; larger feedback traces are not required.

For reference layout, refer to PM6641 Evaluation Kit document.

PM6641 数据表(PDF) 40 Page - STMicroelectronics