The 3.3V power system on AM261x ZFG devices are explored using the AM261x LaunchPad EVM (LP-AM261), from the 3.3V buck output of the PMIC (TPS650366) through the board power planes and ending in at the BGA bulk and per pin decoupling capacitor array. The PMIC 3.3V buck output supplies power for all of the AM261x digital I/O, analog I/O, and the rest of the LaunchPad loads. This is common in most designs where all 3.3V digital level I/O share a common power supply. Additional filtering for the local AM261x 3.3V analog power net is done through the LC filter of ferrite-bead FB2 and associated capacitors. This is used to create a low-IR drop low-pass filter that attenuates the higher frequency switching harmonics of the PMIC buck output.

• Wide 10 mil traces need to be used for all power and ground return via fan-out.
• 3.3V I/O power tends to be shared across multiple devices in the system, recommend routing with very wide power planes across the PCB to minimize IR drops to all components (including AM261x SoC).
• A tightly coupled, adjacent ground return reference plane needs to be used for best transient performance and EMI coupling.
• A wide power plane entry that covers the BGA 3.3V power pin areas need to be used for minimal IR drop and best transient performance.
• Larger packaged, lower-frequency, bulk capacitance needs to be placed adjacent to MCU BGA with vias directly to power plane paths.
• Smaller packaged, higher-frequency decoupling capacitance needs to be placed directly on BGA fan-out vias with as small of a dog-bone to power and ground return vias as possible.

A 1.2V core digital power flow for a 4-layer PCB is under study and can be included in a future revision of this document.