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XRP7714-slide11

Moving into a GM amplifier, the output of the amplifier feeds the ADC. The reason it goes through the error amplifier first is that it makes the range required for the ADC constant for every single output voltage. If it had to support the output voltage directly into the ADC then it would have to support a much larger range and a much larger number of bits on the ADC. The error amplifier feeds into the 7-bit ADC which outputs into the digital PID compensator. The picture above shows the linearity of the error ADC. The accuracy of the system specified in the datasheets is tested by placing a accurate voltage at the feedback, or VOUT, pin and then reading the output of the error ADC. As a result, the 20mV over temp accuracy includes the entire feedback system. In an analog controller in many cases, it only includes just the error amplifier itself. In this case it includes the DAC, the reference, the error amplifier and all the offsets. The slide above shows the linearity of the error ADC.

PTM Published on: 2013-09-19