How to Design for Power Integrity: Selecting a VRM
by Picotest’s Steven Sandler, YouTube, May 05 2016
Focus:
In this 11-min. video, the term VRM is used broadly. Here it refers not only to the dedicated
voltage regulators used to power microprocessors, but any point-of-load regulator (POL) used to
power any board-level circuitry in electronic systems where the regulators, loads, caps and
interconnects form a power distribution network (PDN). Also, the discussion here focuses on
selection of power supply ICs that are used to implement POLs (rather than complete POL
modules), and how designers can 1) select the best ICs and 2) tune the associated POL designs
to achieve flat output impedance. Using state-space averaged models , Steve runs simulations to
demonstrate how voltage-mode control and current-mode control schemes affect output impedance
and PSRR, and how flat impedance can be obtained with these schemes. He also simulates the
effects of transconductance feedback amplifiers used with these control schemes, comparing
series feedback versus shunt feedback for their effect on flatness of the output impedance.
Ultimately, he draws conclusions about the superiority of current-mode control with series
feedback for achieving flat output impedance. The video ends by providing a link to Steve’s ADS
workspace to allow viewers to run these simulations for themselves.
What you’ll learn:
- How to select power supply ICs that are the basis for POL and VRM designs with flat output impedance
- How to design point of load regulators (generic POLs and VRMs) that achieve flat output impedance for better performing PDNs
Notes:
There’s very brief discussion on why flat output impedance is needed for POLs and VRMs, but for a
fuller explanation, see Steve Sandler’s video series, “PDN Basics for Power Designers.â€
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