Issue link: https://resources.mouser.com/i/1527303
Threshold Hysteresis (V TH+ ) There are two main benefits of having threshold hysteresis. First, it provides certainty that your monitored voltage has overcome the threshold level with enough margin before deasserting a reset. Second, it gives room for the power supply to stabilize first before deasserting a reset. There is a tendency for the reset output to produce multiple transitions when processing signals with superimposed noise, as the power supply bounces and recrosses the threshold region (Figure 4). 3 In applications such as industrial environments, noisy signals and voltage fluctuations can occur anytime. Without hysteresis, the reset output will continuously toggle assert and deassert until the power supply stabilizes. It will also put the system into oscillation. Threshold hysteresis cures the oscillation by putting the system hold on reset to prevent the system from unwanted behavior, shown in the blue-shaded area in Figure 4. This helps the supervisor in protecting the system from false resets. Reset Threshold Overdrive vs. Duration Voltage glitches from external factors can occur in any system for either short or long periods. They can also have different magnitudes of voltage dip. Reset threshold overdrive versus transient duration has something to do with the magnitude and duration of the voltage glitch or overdrive. A short-duration glitch with a greater magnitude will not trigger a reset signal to assert, while a less-magnitude overdrive with a longer duration will trigger a reset, as shown in Figure 5. Voltage transients in the monitored supply are ignored depending on their duration. Disregarding these transients will protect your system from nuisance resets such as those caused by short-duration glitches. These glitches can falsely trigger system resets, causing undesirable system behavior. In the product data sheet, the reset threshold overdrive versus duration is often illustrated in one of the typical performance characteristics plots, such as in Figure 6. Any values above the curve will trigger a reset output, while values within the curve will be ignored to prevent the system from false resets. Manual Reset Setup Period (t MR ) and Debounce Time (t DB ) The reset timeout period, threshold overdrive versus duration, and threshold hysteresis all address voltage glitches and transients associated with the monitored voltage, which is usually the power supply of the system microcontroller. For the glitches brought by mechanical contacts such as switches, the manual reset setup period and the debounce time alleviate the possible effects of the voltage transients and glitches. Figure 4: RESET output response without and with threshold hysteresis (reset timeout period not shown to focus on the effect of hysteresis). (Source: Analog Devices) Figure 5: A glitch with a lesser magnitude but occurs in a longer duration will trigger a reset signal as opposed to a short-duration glitch with greater magnitude. (Source: Analog Devices) Figure 6: Asserting of the reset signal will depend on the magnitude of the overdrive and its duration. (Source: Analog Devices) 20 ADI | Powering the Future