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Are We Focused On The Wrong Reference Parameters?

by Steve Sandler, Picotest, Power Electronics Technology, Jan 31 2012

Focus:
Parameters such as dc initial accuracy, temperature coefficient, thermal hysteresis, output noise, reverse current (headroom) and output impedance are usually regarded as the figures of merit (FOMs) for a precision voltage reference. But in this article the author makes the case that these may not be the best FOMs for your particular application. The article identifies the various (and probably lesser known) factors that contribute to voltage reference error and then explores the issues of dynamic and ac performance and control loop stability. Impedance, PSRR, and transient response measurements are performed on an Analog Devices reference. From these measurements, the author concludes that the data sheet does not adequately characterize the ac or transient performance of the reference, and for designers to be able to predict the performance of references in their applications, the voltage reference manufacturers need to specify output impedance (either effective output inductance or ohms/Hz) and PSRR in dB-MHz.

What you’ll learn:

How to understand the importance of ac and transient performance when evaluating voltage references for your application
How to recognize shortcomings in voltage reference data sheets and obtain the specifications you need to properly evaluate these devices

Notes:
Also see "A Simple Method to Determine ESR Requirements for Stable Regulators."

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