Question We want to use the internal reference of the AD7856. We connect only one 100nF on the Refin/Refout pin (4)... We have 3.84V on this pin, I suppose to have 4.096V... Can you confirm that the reference in is normaly at 4.096V if we don't use a external reference on this pin.... Answer 1) The capacitors : The recommendation that the 470nF capacitor be an NPO type is not really required in practice. We have achieved specified performance without an NPO capacitor in place. The reason for the dual decoupling capacitors is to effectively decouple the high frequency bursts of charge which arise in the DAC. So the absolute value of the capacitor is not so important. Any 470nF ceramic capacitor with low ESR, ESL is suitable. The designation of a capacitor as NPO means that it's value does not have a significant positive or negative temperature coefficient. We originally thought that the high equivalent series resistance of high value ceramic capacitors could cause a problem but this turned out not to be the case. I'll ask if we can get the datasheet changed, since this isn't the first enquiry we have had on this point. 2) Vref voltage : Specified on page 7 of the datasheet - 4 REFIN/REFOUT Reference Input/Output. This pin is connected to the internal reference through a series resistor and is the reference source for the analog-to-digital converter. The nominal reference voltage is 4.096 V and this appears at the pin. This pin can be overdriven by an external reference or can be taken as high as AVDD. When this pin is tied to AVDD, or when an externally applied reference approaches AVDD, the CREF1 pin should also be tied to AVDD.

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AD7856 Production
The AD7856 is a high speed, low power, 14-bit Analog-to-Digital Converter (ADC) that operates from a single 5 V power supply. The ADC powers up with a...
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