Output noise voltage is the RMS output noise voltage over a given range of frequencies, typically 10HZ to 100kHz. Noise is measured under the conditions with constant output current and a ripple-free input voltage. To learn more about output noise voltage and how to take an LDO noise measurement, please see How to Measure LDO Noise.

The following sections reviews two noise measurement setup conditions. Conditions were tested on the TPS793 device. Figure 4-4 shows a noise measurement taken with significantly longer cabling, while Figure 4-5 shows a noise measurement taken with significantly shorter cabling. When more cabling is introduced in a noise measurement as seen with Figure 4-4, parasitics are introduced, which means more noise is present in the measurement, which corresponds to the resulting data collection. With parasitics the noise collected in Figure 4-4 was found to be 69.9uVrms, while Figure 4-5, which has minimal parasitics shows data to be 68.9uVrms. Although for this specific application, the noise did not seems to change significantly, only 1uVrms, but with lower noise applications 1uVrms can have a significant impact on how the device can perform.