A power manager circuit is provided. The power manager circuit includes a bandgap reference circuit, first and second monitoring circuits, and a reference buffer. The bandgap reference circuit generates a first voltage, based on an external voltage that is external to the power manager circuit. The first monitoring circuit determines a logical value of a first alarm signal, based on whether a first voltage level of the first voltage is within a first range. The reference buffer generates a second voltage, based on the first voltage. The second monitoring circuit determines a logical value of a second alarm signal, based on whether a second voltage level of the second voltage is within a second range.