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We are having some problems in the field with errors detected by the AD2S1200. In some instances we are getting lower excitation voltage than we expected (3.35V pk-pk compared to 3.6V pk-pk). Although this is within device specification, I would like to know: 1. Does the Loss of Signal feedback level for low and high received signals track the excitation output? In other words, if the excitation amplitude is at the bottom end of the range (3.34V), is the Loss of Signal threshold also at the bottom end of its range (2.9V)? Or could the Loss of Signal threshold be higher? 2. What is the maximum value for the minimum signal amplitude before a fault (LOS or LOT) occurs? Is it 3.0V? 3. What failure mechanisms operate when the received signals (Sin/Cos) have higher amplitude than expected? Is it always LOS and is the level always 3.96V pk-pk? What is the range of values for the high signal amplitude fault? 4. Is it possible to determine from the serial output word whether the fault was high amplitude signal or low amplitude signal?
Please see comments to your questions below. 1. Does the Loss of Signal feedback level for low and high received signals track the excitation output? In other words, if the excitation amplitude is at the bottom end of the range (3.34V), is the Loss of Signal threshold also at the bottom end of its range (2.9V)? Or could the Loss of Signal threshold be higher? PL: The LOS threshold is fixed, internal registers do not update. The typical value is 2.92 volts. The variation in the threshold is due to the variation in the reference voltage. The reference voltage variation also leads to a change in the excitation amplitude. 2. What is the maximum value for the minimum signal amplitude before a fault (LOS or LOT) occurs? Is it 3.0V? PL: LOT does not depend on the amplitude, Loss of tracking (LOT) is detected for three separate conditions: • When the internal error signal of the AD2S1200 has exceeded 5° • When the input signal exceeds the maximum tracking rate of 60,000 rpm (1,000 rps) • When the internal position (at the position integrator) differs from the external position (at the position register) by more than 5° The LOS is default and typically 2.92V. The range is 2.86 min to 3.0 volt max. The variation is due to part to part variation, reference part to part variation and reference drift. 3. What failure mechanisms operate when the received signals (Sin/Cos) have higher amplitude than expected? Is it always LOS and is the level always 3.96V pk-pk? What is the range of values for the high signal amplitude fault? PL: : The DOS is detected is either resolver input exceed the specified DOS Sin/Cos thresholdby comparing the monitor signal to a fixed maximum value. Again the DOS is linked to the reference. The typical value is 4.09V. The range is 4.0 volt to 4.2 volts. 4. Is it possible to determine from the serial output word whether the fault was high amplitude signal or low amplitude signal? PL: The bits in the serial output match the function of the pins. A LOS will indicate with both LOT and DOS low. DOS will indicate with DOS low and LOT high. LOT will indicate with LOT low and DOS high. The faults have a priority, LOS will take precedence over DOS so it should be possible to detect the faults separately. To summarize in general the excitation amplitude will track the input range. For parts with a higher than normal excitation amplitude these parts should have a LOS and DOS at the upper limit. For parts with a lower than normal excitation amplitude these parts should have a LOS and DOS at the lower limit. A 3.35Vp-p excitation voltage would be quite low though. Are the excitation outputs being buffered? The excitation outputs can only supply a small load and therefore should be buffered before going to the resolver. What about the reference voltage level. Is this within specification?