AD2S1200 LOS, DOS and LOT Detection Errors limits?

Document created by analog-archivist Employee on Feb 23, 2016
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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?

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