www.analog.com POWER SUPPLY DESIGN 15 www.power-mag.com Issue 1 2024 Power Electronics Europe 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. Rest and debounce The reset timeout period, threshold overdrive versus duration, and the threshold hysteresis 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 the mechanical contacts such as switches, the manual reset setup period and the debounce time alleviate the possible effects of the voltage transients and glitches. The manual reset setup period (tMR) is the time required for the manual reset to hold and complete before it triggers a reset output. Some supervisors are made to have a long manual reset setup period to add protection to the system. These are common on consumer products on which the button needs to be held for several seconds to reset the system. This method avoids accidental and unintended reset, thus adding protection and reliability. With the manual reset setup period, all the short-duration transients and glitches when pushing on the switch are ignored, as shown in Figure 7a, thus helping the system to be glitch immune. The same concept applies to the debounce time. Like the setup period, debounce time (tDB) ignores the high frequency periodic voltage transients when pushing on or off a switch. These high frequency transients are considered invalid and do not trigger a reset as shown in Figure 7b. When the signal exceeds the debounce time, that is the time it will be considered a valid input signal from a switch or a push button. Conclusion Without voltage supervisors, systems are at risk of brownout conditions and malfunction during voltage transients and glitches. Voltage supervisors solve this by putting processors into reset mode during such scenarios, All the parameters discussed here, including reset timeout period, threshold hysteresis, threshold overdrive, manual reset setup period and debounce time, improve the reliability of voltage supervisors in monitoring power supply voltages by making them immune to glitches and transients. This gives stability and reliability to overall system performance. Figure 7: The manual reset setup period and debounce time diagram of a supervisor with a long manual reset setup period (MAX6444). The manual reset setup period (tMR) needs to be completed first before a reset signal asserts (a) and debounce time (tDB) is required (b) to be considered as a valid input signal. Figure 6: Asserting of the reset signal will depend on the magnitude of the overdrive and its duration. Figure 5: A glitch with a less magnitude but occurs in a longer duration will trigger a reset signal as opposed to a short-duration glitch with greater magnitude.
RkJQdWJsaXNoZXIy MjQ0NzM=