Application details

L6726A

20/24

8.5

Embedding L6726A-based VRs…

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

VR 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 MBs have become faster and more

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

produced by the VR can affect data integrity if additional layout guidelines are not followed.

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):

When reproducing high current path on internal layers, keep all layers the same size in order

to avoid "surrounding" effects that increase noise coupling.

Keep safe guard distance between high current switching VR traces and data busses,

especially if high-speed data busses, 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 VR.

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

and Input voltage path (from input bulk capacitors and HS drain). Also GND connection

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

carefully kept far away from noise-sensitive data busses.

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

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

in addition to the previous guidelines, to reduce the current slope and thus 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.