voltage, and the voltage differential. Output noise The noise from the LDO itself must also be considered in filter design. Like other electronic devices, LDOs are affected by thermal noise, bipolar shot noise, and flicker noise. Each of these phenomena contribute noise to the output voltage, mostly concentrated over the lower end of the frequency spectrum. In order to properly filter AC frequencies, an LDO must both reject ripple at the input while introducing minimal noise at the output. Efforts to attenuate ripple from the input voltage could be in vain if a noisy LDO just adds that noise back again at the output. Load regulation Load regulation is a measure of the circuit’s ability to maintain the specified output voltage under varying load conditions. Load regulation is defined as: The worst case of the output voltage variations occurs as the load current transitions from zero to its maximum rated value or vice versa. Line regulation Line regulation is a measure of the circuit’s ability to maintain the specified output voltage with varying input voltage. Line regulation is defined as: Like load regulation, line regulation is a steady state parameter—all frequency components are neglected. Increasing DC open-loop current gain improves the line regulation. Transient response The transient response is the maximum allowable output voltage variation for a load current step change. The transient response is a function of the output capacitor value (), the equivalent series resistance (ESR) of the output capacitor, the bypass capacitor () that is usually added to the output capacitor to improve the load transient response, and the maximum load-current (). The maximum transient voltage variation is defined as follows: Where corresponds to the closed-loop bandwidth of an LDO regulator. is the voltage variation resulting from the presence of the ESR () of the output capacitor. The application determines how low this value should be. Evolution and the future A competitor to the LDO, the IVR (integrated voltage regulator) appears to offer solutions to many of the issues with efficiency and performance that LDO regulators suffer. IVRs combine a switching voltage regulator with all necessary control circuitry into a single device which results in a 10x size reduction and 10-50% energy savings. See also Linear regulator Low-voltage detect (sometimes confused with LDO regulator} Voltage regulator Switched-mode power supply List of linear integrated circuits LM7805 References External links Understanding Low Dropout Regulators - Basics Understanding LDO Regulators