A device containing digital circuits needs to be properly powered up to ensure that the digital gates are initialized in a known state. This is important at initial device power-up as well as after an unscheduled power interruption or a power supply “brown-out” event.
This application note addresses the power-up management and partial loss of power events such as “brown-outs” and design considerations related to the Hittite RF PLL+VCO product lines. It should be noted that many of the concepts and recommendations in this note are applicable to all digital IC's.
It is commonly known that applying voltages to IC signal pins prior to application of power can result in a state known as „Latch-Up‟. Latch-Up injects charge into the substrate of the device and can cause the device to malfunction or create a short circuit across power supply rails through parasitic connections inside the IC. The Latch-Up state can only be cleared by first removing the offending signal voltage , then cycling power off, waiting, powering on and then applying the signal again. If left unchecked, Latch-Up can result in damage due to the excess current through the device.