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Guide to DC/DC converter PCB layout (Part 2)

07 Jul 2015  | Timothy Hegarty

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The noise-sensitive small-signal components for the compensation network, feedback resistors, frequency set resistor, soft-start capacitor and current sense filter are located close to their respective pins (COMP, FB, RT, SS, CS, CSG) and have a dedicated analogue ground (AGND) plane that ties to the IC's AGND pin. Power ground (PGND) connects to the exposed pad of the IC with thermal vias to inner ground planes. PGND connects to AGND locally there as well for single-point grounding.


Summary
Reducing converter losses is an essential requirement to enable compact realisation and a flexible deployment of the converter within the intended system. Thoughtful placement and layout of the power stage components in a PCB design enable better switching performance, higher efficiency, lower operating temperatures and reduced broadband EMI for easier regulatory compliance [8].

Stay tuned for part 3 of this series, when I'll delve into the detail of routing critical traces for gate drives, output voltage feedback and current sense, and finally ground management, in tandem with a polygon plane design of the outer and inner layers of the multi-layer PCB.


References

1. T. Hegarty. "DC/DC converter PCB layout, Part 1"

2. LM5175EVM-HD 400kHz buck-boost converter design

3. T. Meade et al. "Parasitic inductance effect on switching losses for a high frequency DC/DC converter." APEC 2008, pp. 3-9

4. Bhargava et al. "DC/DC buck converter EMI reduction using PCB layout modification." IEEE Transactions on EMC, August 2011, pp. 806-813

5. Reusch et al. "Understanding the effect of PCB layout on circuit performance in a high frequency gallium nitride based point of load converter." APEC 2013, pp. 649-655

6. K.W. Kam et al. "EMC guideline for synchronous buck converter design." 2009 IEEE International Symposium on EMC, pp. 47-52

7. M. Montrose. "Printed Circuit Board Design Techniques for EMC Compliance: A Handbook for Designers," second edition. IEEE Press, 2000

8. "Low Radiated EMI Layout Made SIMPLE with LM4360x and LM4600x." TI application note (SNVA721A), September 2014

9. T. Hegarty. "Paralleling electrolytic and ceramic capacitors perks up POL transient response." How2Power, March 2011


About the author
Timothy Hegarty is a Systems and Applications Engineer in the Power Products Solutions Unit at Texas Instruments, United States. He received the bachelor's and master's degrees in Electrical Engineering from University College Cork, Ireland in 1995 and 1997, respectively. Prior to Texas Instruments, he worked for National Semiconductor, Artesyn Technologies, and Melcher. His areas of interest are high-efficiency isolated and non-isolated converters, wide input voltage range PWM regulators and controllers, resonant converters, renewable energy systems, and system-level simulation of same. He is a member of the IEEE Power Electronics Society.


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