Question
Now there is one customer would like to use AD2S80A to replace our older and high price parts RDC1740 and RDC1742. But she encountered the problemthat her input signals are 16V, which is higher than AD2S80A can tolerate. Fortunately, there is one application note AN-265 (in the attachment)described the solution in details. But the transformer 5S70 and 5S72 are obsolete now.The questions are:1. Whether we have any parts to replace 5S70 and 5S72?2. If these two parts are not available, whether we can say that the resistor attenuation can ensure the performance of AD2S80A? If can, whichkind of resistors and which tolerance should be selected?3. Whether there is the third way to do that?
Answer
Thank you for your email concerning the AD2S80A. The answers to yourquestions are as follows:1. No, we do not have any parts to replace the 5S70 and the 5S72.2. As the Apps note, AN-265, pointed out it is the matching of theresistors, R3, R4, R5 & R6, that is important and not the actual values.The tolerance should be as tight as possible. An example is given inthe Apps note which suggests that if there is a 1% error in the ratioR3/R4 : R5/R6 i.e. caused by a combination of matching and/or toleranceof the resistors this will result in a 16.7 arc min additional error through theconverter i.e. 1% = 10,000ppm, => Error = 1,000 arc seconds = 16.7 arc min.3. The only other method I can suggest may not be practical for your customer.If possible, I would recommend that they reduce the amplitude of the referencevoltage which is being applied to the resolver, which results in lower amplitudeSin and Cos outputs. The advantage of this method is that any errors introducedon the reference excitation is seen equally on both Sin and Cos signals andas a result cancelled out.However, as I mentioned, this may not be practical for your customer.
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