Characterizing the VRM

Eastern Time September 12, 2019 11:00 am - 11:30 am

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Steve Sandler

A high fidelity VRM model is required to properly assess system performance, and this includes power integrity (PI). This has always been my position and I have presented papers, videos and lectures on the topic. Most recently I wrote an article, published in the July 2019 Signal Integrity Journal, illustrating the interactions between the VRM and the system. This clearly shows why full VRM characterization is essential.

In this session I’ll show the test bench setup to perform the measurements needed to characterize the predominant VRM noise paths:

  1. Input self-Impedance (predominantly negative resistance for a switching regulator)
  2. Output self-impedance (Generally used for target impedance assessment)
  3. Input to output transfer (input voltage to output voltage transmission (PSRR))
  4. Output to Input or Reverse transfer (output current to input current transmission)
  5. Input noise current (predominantly switching induced)
  6. Output noise (predominantly switching induced)

These measurements provide a roadmap to optimizing the VRM from a system level perspective, ensuring power integrity, while minimizing VRM noise that degrades performance of other system circuits.