2 General Overview

The HLVD is a necessary power supply monitoring feature in numerous battery-powered applications, where the supply voltage of a microcontroller may fall below the specified threshold level and require battery replacement or recharging for the uninterrupted operation of the microcontroller. The HLVD feature is capable of monitoring the supply voltage of a microcontroller which is directly powered by a battery power source. The HLVD-based voltage monitoring circuitry has several advantages over an ADC-based voltage monitoring circuit, as listed below:

  1. The microcontroller PORT pins are not required to implement the supply voltage monitor.
  2. This module does not require external components, and hence no excess power consumption by the external circuitry.
  3. The HLVD module uses an internal bandgap reference and draws a typical of 22 µA when enabled. It can be disabled except when needed to reduce even this tiny current draw.
  4. It can generate an interrupt when VDD is below or above the selected trip point (depending on how it is configured).
    Note:
    1. The HLVD can only be used to measure the supply voltage of the microcontroller (i.e., VDD), so it cannot be used to monitor a battery supplying power through a voltage regulator.
    2. There are 16 steps over the measurement range with manufacturing tolerances on the bandgap reference and internal resistive voltage divider. The trip point settings shown below in Table 4-1 are available for a PIC18-Q10 family of devices. The trip point settings depend on the device used. Refer to the device data sheet for more details.