L6711 datasheet(47/50 Pages) STMICROELECTRONICS

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L6711

Embedding L6711-based VRDs...

47/50

Embedding L6711-based VRDs...

When embedding the VRD into the application, additional care must be taken since the

whole VRD is a switching DC/DC regulator and the most common system in which it has to

work is a digital system such as MB or similar. In fact, latest MB has become faster and

powerful: high speed data bus are more and more common and switching-induced noise

produced by the VRD can affect data integrity if not following additional layout guidelines.

Few easy points must be considered mainly when routing traces in which switching high

currents flow (switching high currents cause voltage spikes across the stray inductance of

the traces causing noise that can affect the near traces):

Keep safe guarding distance between high current switching VRD traces and data buses,

especially if high-speed data bus to minimize noise coupling.

Keep safe guard distance or filter properly when routing bias traces for I/O sub-systems that

must walk near the VRD.

Possible causes of noise can be located in the PHASE connections, Mosfet gate drive and

Input voltage path (from input bulk capacitors and HS drain). Also PGND connections must

be considered if not insisting on a power ground plane. These connections must be carefully

kept far away from noise-sensitive data bus.

Since the generated noise is mainly due to the switching activity of the VRM, noise

emissions depend on how fast the current switch. To reduce noise emission levels, it is also

possible, in addition to the previous guidelines, to reduce the current slope and then to

increase the switching times: this will cause, as a consequence of the higher switching time,

an increase in switching losses that must be considered in the thermal design of the system.

L6711 Datasheet(PDF) 47 Page - STMicroelectronics