Monitoring & metering
operating stably, such as in Figure 5b. Figure 6 illustrates an example of monitoring a 2.5V core voltage with ±5% tolerance specification using two window voltage supervisors with different threshold accuracies. The tolerance window used in this example may not be the actual available options but were chosen to account for the threshold accuracy. The window voltage supervisor used has a threshold accuracy of ±1.5% and ±0.3% for figures 6a and 6b, respectively. When using a ±1.5% threshold accuracy, the optimum tolerance window to avoid operating in a malfunction region shown in Figure 6a is ±3.5%. This results in a power supply operating window of 100mV. While with a ±0.3% threshold accuracy, the optimum tolerance window that maximises the power supply is ±4.7% without any malfunction risks. These values set will give a power supply operating window of 220mV. This difference in the accuracy improves the operating power supply window by more than double, maximising the power supply performance.
The above calculations were obtained using the Window Voltage Monitor Calculator, a tool that aids to easily understand and visualise the different parameters in a window voltage supervisor. This also allows users to check whether the device specifications fit the design requirements such as the power supply operating window. This tool is available for download from the following product pages: MAX16138, MAX16191, MAX16193, MAX16132/MAX16133/MAX16134/ MAX16135, MAX16137.
With continuous improvement in the architecture and performance of window voltage supervisors to address the demand of core voltages getting lower, threshold accuracies can now range from as high as ±1.5% to ±0.3%. And to enhance precision, window voltage supervisors with a factory-trimmed nominal monitored voltage and tolerance window are available. The MAX16193, a ±0.3% accuracy dual-channel supervisory circuit, is the industry’s window voltage supervisor with the highest threshold accuracy across different temperatures as of year 2024. A variety of factory-trimmed tolerance windows from ±2% to ±5% are available to accommodate different supply voltages and tolerances for industrial and automotive applications. In the typical application circuit in Figure 7, input channel 1 (IN1) monitors low core voltage rails from a 0.6V to 0.9V threshold range with ±0.3% accuracy, while input channel 2 (IN2) monitors higher system rails from a 0.9V to 3.3V threshold range with ±0.3% accuracy.
The MAX16193’s threshold accuracy specification is true for all temperatures within the operating range of -40°C to +125°C. Figures 8a and 8b show that the high threshold accuracy of the device for the two inputs IN1 and IN2 is true at different temperatures. While
Instrumentation Monthly August 2025
Figure 6. Effective operating power supply window with (a) ±1.5% threshold accuracy and (b) ±0.3%
Figure 7. Typical application circuit of
MAX16193, industry’s window supervisor with the highest threshold accuracy across temperature monitoring the core and input/output supply voltage of an MCU.
Figure 8. UV and OV threshold accuracy plots over temperature for (a) IN1 and (b) IN2.
other voltage supervisors have the optimum performance only on certain range, this device guarantees high accuracy from the minimum up to the maximum operating temperature.
CONCLUSION
To keep up with the demand in speed, power optimisation, and along with advancing process technology, core voltages of devices are getting lower, and the tolerance is getting tighter. Window voltage supervisors help prevent serious
problems in these devices. However, threshold accuracy plays a great part in operating within the device specification window. High threshold accuracy of window voltage supervisors helps maximise the power supply performance by improving the operating power supply window, thus preventing unwanted frequent resets and system oscillation.
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