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We all know very well that the embedded systems require highly regulated voltage supplies to function effectively. It is for a fact that, that the thresholds in a given embedded electronics design must be always taken into account, or we run the risk of signal weakening, noise, or erratic system behaviour which are all very difficult to track down. There is nothing like a perfect over design of the power supply, in order to get rid of the possible spurious behaviour of the embedded system.
Specially so, the electronic designs most prone to the noise due to power supply are the analogue to digital conversion circuits (ADC), very true also for the completely digital embedded type of ADC designs in a chip separately, or even the embedded designs present on a chip such as the ARM7 or Cortex series of microcontrollers from Atmel or Texas Instruments, with high data rates and high resolutions. Such circuits may be operating as the peak of their performance, at times almost approaching the threshold of both the embedded system's maximum signal stability rating, as well as the data transfer rating of the particular system's bus speed.
In such systems, it is generally a good idea to have a suitable and proven power supply design at hand which is also highly accurate and has optimally low temperature drift, a significant factor in the design of accurate power supplies. The temperature drift can significantly affect a good power supply design if it is not taken into account. In order to give my discussion a meaning, I have chosen an LDO (low dropout) chip from Analogue Devices, the ADP3334, from the ADP333x series. According to the datasheet, this device only has 0.9% temperature drift at room temperature, and only 1.8% under the full temperature range, from -40 to 85 degrees centigrade, which are actually quite good factors, with very few devices capable of delivering this accuracy at an affordable price and ease of use. It only requires a capacitor at its input and output for voltage regulation, and two resistors forming a resistor divider setting the output voltage, and a capacitor providing high frequency noise bypass, which is more or less what you get with all adjustable regulators. What's amazing is that the device is even adjustable, with a resistive divider setting the output voltage between 1.5 volts to 10 volts, provided the input stays at least 0.4 volts above the desired output voltage under the worst case condition and does not exceed 11 volts, the worst case being 500 mA being drawn from the device. This device only needs an input of 200 mV higher than its regulated output voltage, if the current drawn does not exceed 100 mA and the input is relatively stable.
For more information about the device pinout and setting the resistor divider values refer to the datasheet link right at the bottom of this article, which conveniently provides a table of possible resistor values, the rule being none of them fall below 50 kilo ohms and are 1% accuracy, and the output voltage is calculated as Vout=1.178*(R1/R2+1) , again very simple for this much accuracy. Needless to say the various packaging types available for the device, including the famous SOIC 8 pin, which is compatible with most of the embedded system designs.
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