PM6686 STMicroelectronics, PM6686 Datasheet - Page 45

• Manufacturer Part Number: PM6686
• Description: Dual Step-down Controller With Adjustable Voltages, Adjustable Ldo And Auxiliary Charge Pump Controller For Notebook
• Manufacturer: STMicroelectronics

PM6686
12
PCB design guidelines
The layout is very important in terms of efficiency, stability and noise of the system. It is
possible to refer to the PM6686 demonstration board for a complete layout example.
For good PC board layout follows these guidelines:
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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 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 references, 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 vias connection is preferable to a 0 Ω 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
As general rule, make the high-side and low-side drivers traces wide and short.
The high-side driver is powered by the bootstrap circuit. It’s very important to place
capacitor CBOOT as near as possible to the BOOT pin (for example on the layer
opposite to the device). Route HGATE and PHASE traces as near as possible in order
to minimize the area between them.
The low-side gate driver is powered by PVCC pin. Placing PGND and LGATE pins near
the low-side MOSFETs reduces the length of the traces and the crosstalk noise
between the two sections.
The linear regulator outputs are referred to SGND as long as the reference voltages
VREF2 and VREF3. Place their output filtering capacitors as near as possible to the
device.
Place input filtering capacitors near PVCC, VCC and VIN pins.
Doc ID 15281 Rev 4
Figure 58
). The first priority is to minimize
Figure 58
PCB design guidelines
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