Application Note AN-932
2008
Martin Murnane, Chris Augusta
Powering up a circuit on a printed circuit board is too often taken for granted and can cause damage and both destructive and nondestructive latch-up conditions. These problems may not be prominent until volume production begins when the tolerances of devices and designs are put to the test. This is dangerously late in the process and extremely expensive, with respect to time and the delivery of projects and products. Errors found at this stage result in numerous modifications, including PCB layout changes, design alterations, and extra anomalies. With the advent of incorporating many functional blocks into one integrated circuit (IC), this has resulted in supplying these blocks with multiple, sometimes equal, or in many instances, differing voltage supplies. As more and more of these systemon-a-chip (SoC) ICs proliferate the marketplace, the need for particular power supply sequencing and power management issues arises.
There is usually enough information in datasheets from Analog Devices, to guide a designer to a correct power-up sequence for an individual IC. However, some ICs specifically require a well-defined power-up sequence. This is true in the case of many of ICs from Analog Devices and is quite common in ones using multiple supplies such as converters (consisting of both analog-to-digital converters (ADCs) and digital-to-analog converters (DACs), digital signal processors (DSPs), audio/ video, radio frequency, and many other mixed signal ICs. Essentially, any IC containing some analog input/output with a digital engine falls into this category, where particular power sequencing may be required. On these ICs, there could be separate analog and digital supplies and some may even have a digital input/output supply, as detailed in specific examples discussed in the following sections.
This application note looks at some of the more subtle power supply issues that a designer must consider in new designs, especially when there are several different power supplies required for an IC. Some of the more common supplies presently are: +1.8 V, +2.0 V, +2.5 V, +3.3 V, +5 V, -5 V, +12 V, and -12 V. With over 10,000 different products worldwide from Analog Devices, the scope of this application note looks only at a few ADCs. However, these supply sequencing considerations can be applied to practically any mixed signal IC from Analog Devices.
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