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

2.3 Separating Differential Sense Lines From Power Planes

The most frequently encountered issue in layout is the incorrect routing of differential sense signals from the sense resistor to TI’s LM5177 integrated circuit (IC) pins (the CSA-CSB pair).

Use Kelvin connections to RSENSE (R3, R4, R5) for the current sense signals CSA and CSB and run the lines in parallel from the RSENSE terminals to the IC pins. Avoid crossing noisy areas such as SW1 and SW2 nodes or high-side and low-side gate drive traces. Place the filter capacitor for the current sense signal as close to the IC pins as possible.

In the case of LM5177, one of the sense nodes CSA is electrically the same as SW1. SW1 needs to use a separate routing to avoid noise getting picked up, as this is the return path of the buck high side switch.