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Henry Zhang, Sr Director, Applications
Engineering, Analog Devices, Inc.
Henry Zhang is senior director of
Analog Devices, Inc., Power by Linear™
applications. He received an MS and a PhD
in electrical engineering from the Center for
Power Electronics Systems at Virginia Tech
in 1998 and 2001, respectively. Henry's
work interests include power supply
and power management system design
and optimization tools, power converter
modeling and control, advanced power
topologies, integrated power solutions, and
high-frequency power techniques.
The purpose of a power distribution network (PDN) is to provide power to a system
driven by an application-specific integrated circuit (ASIC), CPU or field-programmable
gate array (FPGA) without degrading signal integrity. As power devices become
smaller while load devices need more power, power devices require greater power
density. Low-impedance PDNs usually require more decoupling capacitors with
increased board area and cost. The challenge is how to build low-impedance PDNs
that deliver more power with improved efficiency and take up less room on the
printed circuit board (PCB). Several PDN design and technology trends help address
these challenges:
• Output capacitor choices. A low-impedance PDN requires using capacitors that
minimize impedance to minimize the power supply's transient response ripple
to load changes. Larger capacitors provide the energy to handle low-frequency
transient response. Smaller capacitors with lower parasitic resistance (ESR) and
inductance (ESL) are able to lower PDN impedance at higher frequencies even
beyond the supply loop bandwidth. To meet the minimum impedance target for
a PDN, engineers place a combination of capacitor sizes in parallel, creating a
capacitor network that delivers low or flat impedance over a wide frequency range.
Higher Switching Frequency with Greater Power
Efficiency Is the Key
"The challenge is how to build low-impedance PDNs
that deliver more power with improved efficiency and
take up less room on the printed circuit board."
