VDD pin is monitored by the internal comparator with integrated reference to indicate when VDD falls below the fixed threshold voltage. VDD also functions as the supply for the following:

• Internal bandgap (reference voltage)
• Internal regulator
• State machine
• Buffers
• Other control logic blocks

Good design practice involves placing a 0.1µF to 1µF bypass capacitor at VDD input for noisy applications and to make sure enough charge is available for the device to power up correctly. The reset output is undefined when VDD is below V_POR.