38.5 Applications
In many applications, it is desirable to detect a drop below, or rise above, a particular voltage threshold. For example, the HLVD module can 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 indicates a High-Voltage Detect from, for example, 3.3V to 5V (the voltage on USB) and vice versa for a detach. This feature can save a design a few extra components and an attach signal (input pin).
For general battery applications, the figure below 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. The interrupt can cause the execution of an Interrupt Service Routine (ISR), which will allow the application to perform “housekeeping tasks” and a controlled shutdown before the device voltage exits the valid operating range at TB. This will give the application a time window, represented by the difference between TA and TB, to safely exit.
