SLVAFJ3 september   2023 LM5177 , LM51772

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Importance of DC-DC Power Supply Layout
  5. 2Steps for a Good Layout
    1. 2.1 Identifying Critical Circuit Paths
    2. 2.2 Optimizing Hot Loops in the Power Stage
    3. 2.3 Separating Differential Sense Lines From Power Planes
      1. 2.3.1 Using Net Ties to Separate Routing
    4. 2.4 Routing Gate-Drive and Return Paths
    5. 2.5 Controller Layout
    6. 2.6 Separate AGND and PGND
    7. 2.7 Thermal Vias
  6. 3Tips for Layout Optimization
  7. 4Layout Example
  8. 5Summary
  9. 6References

2.6 Separate AGND and PGND

In power supply layout, separating the signal system is important, such as the feedback path which is susceptible to noise and the switching nodes that switch large current. The same hold good for the ground wiring too which requires special considerations.

  • AGND: a quiet ground reference for control signals (analog ground)
  • PGND: a noisy ground reference for power signals (power ground)

AGND is used for the ground lines that are susceptible to noise such as feedback pins and PGND is used as return path for large current signals.

Though the DC ground potential is the same, measure must be taken to separate these AGND and PGND planes to make sure noise arising from digital or high-power signals is not conducted between them to interfere with analog signals. AGND is used for control signals and should be closer to the IC and should have its own polygon. It is also important to make sure AGND and PGND are on the same potential and ultimately should be connected together at one point.

Also, it is recommended having two ground signs in your schematic already as it becomes difficult to visualize sensitive and noisy potentials on the layout if the same GND sign is used on the schematic. Hence, it is better to start with split GND in the schematic level and connect them with a net tie.