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How Voltage Supervisors Address Power Supply Noise and Glitches By Noel Tenorio, Product Applications Manager, Analog Devices, Inc. Introduction Applications that compute and process data requiring field programmable gate arrays (FPGAs), microprocessors, digital signal processors, and microcontrollers depend on safe and reliable operations. These devices are taxing on power supply requirements, as they are only allowed to operate at a certain range of power supply tolerance. 1 Voltage supervisors are known solutions to achieve system reliability. They can act immediately to put the system in reset mode when an unexpected failure from the power supply arises, such as undervoltage or overvoltage. However, monitoring voltages in power supply rails always comes with some nuisances that can trigger unwanted false reset outputs. These are power supply noises, voltage transients, and glitches that can come from the power supply circuit itself. This article discusses the different parameters in a voltage supervisor that address unwanted power supply noises, voltage transients, and glitches. It also discusses how these parameters improve the dependability of voltage supervisors when monitoring power supplies, increasing the system's reliability in the application. Power Supply Noise, Voltage Transients, and Glitches in a System Power supplies have inherent imperfections. There are always noise artifacts coupled on the DC that can come from the power supply circuit component itself, noise from other power supplies, and other noise generated from the system. These problems can worsen if the DC power supply is a switch-mode power supply (SMPS). SMPSs produce a switching ripple that is coherently related to the switching frequency. They also produce high-frequency switching transients that occur during switching transitions. These transitions are caused by the fast on-and-off switching of the power MOSFETs. Figure 1 shows an application circuit in which the MAX705 supervisor is used to monitor any failure in the output of the switching regulator, which is the voltage supply of the microcontroller. Aside from the steady-state operation noise artifacts, there are also scenarios in the power supply where voltage transients are more pronounced. During startup, a voltage output overshoot is usually observed related to the feedback-loop response of the power supply, followed by voltage ringing for some time until it reaches stability. This ringing can be worse if the feedback loop compensation values are not optimized. Voltage overshoot and undershoot can also be observed during transient or dynamic loading. In the applications, there are times when the load needs more current to execute complex processes, which leads to a voltage undershoot. Figure 1: The MAX705 supervisor is used to monitor a switching regulator output, which is the input voltage supply of a microcontroller. (Source: Analog Devices) Adobe Stock / luchschenF – stock.adobe.com MAX16162 nanoPower Supply Supervisor LEARN MORE 18 ADI | Powering the Future