PM6681A STMicroelectronics, PM6681A Datasheet - Page 42

• Manufacturer Part Number: PM6681A
• Description: Dual synchronous step down controller with adjustable LDO
• Manufacturer: STMicroelectronics

Layout guidelines
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Layout guidelines
The layout is very important in terms of efficiency, stability and noise of the system. It is
possible to refer to the PM6681A demonstration board for a complete layout example.
For good PC board layout follows these guidelines:
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Figure 44. Current paths, ground connection and driver traces layout
Place on the top side all the power components (inductors, input and output capacitors,
MOSFETs and diodes). Refer them to a power ground plan, PGND. If possible, reserve
a layer to PGND plan. The PGND plan is the same for both the switching sections.
AC current paths layout is very critical (see
their length. Trace the LS MOSFET connection to PGND plan (with or without current
sense resistor RSENSE) as short as possible. Place the synchronous diode D near the
LS MOSFET. Connect the LS MOSFET drain to the switching node with a short trace.
Place input capacitors near HS MOSFET drain. It is recommended to use the same
input voltage plan for both the switching sections, in order to put together all input
capacitors.
Place all the sensitive analog signals (feedbacks, voltage reference and current sense
paths) on the bottom side of the board or in an inner layer. Isolate them from the power
top side with a signal ground layer, SGND. Connect the SGND and PGND plans only in
one point (a multiple via connection is preferable to a 0 ohm resistor connection) near
the PGND device pin. Place the device on the top or on the bottom size and connect
the exposed pad and the SGND pins to the SGND plan (see
Figure 44
). The first priority is to minimize
Figure 44
).
PM6681A