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RF PLL+VCO Power-Up & Brown-Out Design Considerations

RF PLL+VCO Power-Up & Brown-Out Design Considerations

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.



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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.

 




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