How to Design for Power Integrity: Selecting a VRM

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.”

View the Source

Author & Publication:

Picotest’s Steven Sandler, YouTube, May 05 2016

This article summary appears
in the HOW2POWER Design Guide.

The Design Guide offers
organized access to
hundreds of articles
on dozens of power conversion
and power management topics.

The Design Guide search results
include exclusive summaries
and accurate "how to" analysis
to help you make faster,
more informed decisions.

Search
for more articles