A power supply monitor includes a delta-sigma modulator including an input receiving a binary number and an output providing a pulse-density modulated signal, the delta-sigma modulator operable to scale the pulse-density modulated signal based on the binary number. A fast droop detector circuit includes a level shifter providing the modulated signal referenced to a clean supply voltage. A lowpass filter is coupled between the level shifter and a comparator. The comparator produces a droop detection signal at said output responsive to a monitored supply voltage dropping below a predetermined level relative to the filtered signal.