The internal reference voltage of the HLVD module, specified in electrical specification parameter D420, may be used by other internal circuitry, such as the Programmable Brown-out Reset. If the HLVD or other circuits using the voltage reference are disabled to lower the device’s current consumption when carry out Microcontroller SN8P2203 Heximal Extraction, the reference voltage circuit will require time to become stable before a low or high-voltage condition can be reliably detected. This start-up time, TIRVST, is an interval that is independent of device clock speed.

It is specified in electrical specification parameter 36.The HLVD interrupt flag is not enabled until TIRVST has expired and a stable reference voltage is reached.In many applications, the ability to detect a drop below or rise above a particular threshold is desirable.

For example, the HLVD module could be periodically enabled to detect Universal Serial Bus (USB) attach or detach. This assumes the device is powered by a lower voltage source than the USB when detached. An attach would indicate a high-voltage detect from, for example, 3.3V to 5V (the voltage on USB) and vice versa for a detach.

This feature could save a design a few extra components and an attach signal (input pin). For general battery applications, Figure 22-4 shows a possible voltage curve. Over time, the device voltage decreases. When the device voltage reaches voltage VA, the HLVD logic generates an interrupt at time TA before Microcontroller SN8P2203 Heximal Extraction.

The interrupt could cause the execution of an ISR, which would allow the application to perform “house-keeping tasks” and perform a controlled shutdown before the device voltage exits the valid operating range at TB. The HLVD, thus, would give the application a time window, represented by the difference between TA and TB, to safely exit.