LDO PSRR Measurement Simplified

by Sanjay Pithadia and Scot Lester, Vendor website, Jul 01 2009

Focus:
A 4-page application note explains methods of measuring the power supply rejection ratio (PSRR, also known as power supply ripple rejection) of a low-dropout linear regulator (LDO). Two methods are described for injecting the input noise signal—the LC summing node and the summing amplifier. In the recommended approach, the summing amplifier is combined with a network analyzer, which generates input signals and measures input and output signals on the LDO. A diagram for a test setup is given showing details of the summing amp and analyzer. But for those without a network analyzer, a method using an oscilloscope is described. The advantages and limitations of the different methods as well tips for applying them are discussed.

What you’ll learn:

• How to measure LDO PSRR using a network analyzer or oscilloscope in combination with a summing amp or summing node
• How to understand the pros and cons of different methods of measuring LDO PSRR

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