ST1S40IPUR datasheet(19/30 Pages) STMICROELECTRONICS

19 / 30 page

ST1S40

Application information

Doc ID 17928 Rev 4

19/30

In order to prevent dynamic unbalance between VINSW and VINA, the trace connecting the

VINA pin to the input must be derived from VINSW.

The feedback pin (FB) connection to the external resistor divider is a high impedance node,

so the interferences can be minimized through the routing of the feedback node with a very

short trace and as far as possible from the high current paths.

A single point connection from signal ground to power ground is suggested.

Thanks to the exposed pad of the device, the ground plane helps to reduce the thermal

resistance junction to ambient; so a large ground plane, soldered to the exposed pad,

enhances the thermal performance of the converter allowing high power conversion.

Figure 8.

PCB layout guidelines

Input cap as close as possible

to VINSW pin

Star center for common ground

Short FB trace

VINA derived from Cin

To avoid dynamic voltage drop

Between VINA and VINSW

Short high switching

current loop

Via to connect the thermal pad

To bottom or inner ground plane

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