Power Supply Rejection Ratio (PSRR) for LDOs is a measure of how well a small-signal ripple on the input is attenuated at the output. To learn more about PSRR and how to take a PSRR measurement, please see LDO PSRR Measurement Simplified.

In the following section, we review two PSRR measurement setup conditions taken with the TPS793 device, shown throughFigure 4-3. Condition one, shown with the red trace, shows a PSRR measurement taken with significantly longer cabling, while condition two, shown with the green trace, shows a PSRR measurement taken with significantly shorter cabling. When parasitics are introduced in a PSRR measurement, as shown with red trace, the PSRR measurement data collected at higher frequencies seems to be lower. At higher frequency measurements, especially for PSRR, the output capacitor characteristics significantly affects the measurement. With more parasitics tied to the output capacitor, the data collected at high frequencies shows the capacitor characteristics with those parasitics introduced.