# HLVD Start-Up Time

If the HLVD or other circuits using the internal voltage reference are disabled to lower the device’s current consumption, 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, TFVRST, is an interval that is independent of device clock speed. It is specified in the “Electrical Specifications” chapter of the device specific data sheet.

The HLVD interrupt flag is not enabled until TFVRST has expired and a stable reference voltage is reached. For this reason, brief excursions beyond the set point may not be detected during this interval (see the figures below).

Figure 1. Low-Voltage Detect Operation (INTL = 1)
Figure 2. High-Voltage Detect Operation (INTH = 1)