© 2016 Integrated Device Technology, Inc.
3.6.2.7. SOT Interpretation
SOT is a 2
nd
order term that can apply to one and only one of the following: bridge non-linearity correction, Tco
non-linearity correction, or Tcg non-linearity correction.
As it applies to bridge non-linearity correction:
Resolution: 0.25% @ Full Scale
2
nd
order correction SOT_BR is possible up to +5%/-6.2% full scale difference from the ideal fit (straight line),
because the SOT coefficient values are limited to the range of (0xC0 = -0.25
dec
) to (0x7F = 0.4960938
dec
).
(Saturation in internal arithmetic will occur at greater negative non-linearities.)
Limitation: Using any calibration method for which SOT is applied to the bridge measurement (SOT_BR), there
is a possibility of calibration math overflow. This only occurs if the sensor input exceeds 200% of the calibrated full
span, which means the highest applied sensor input should never go higher than this value.
Example: This example of the limitation when SOT is applied to the bridge reading uses a pressure sensor bridge
that outputs -10 mV at the lowest pressure of interest. That point is calibrated to read 0%. The same sensor
outputs +40 mV at the highest pressure of interest. That point is calibrated to read 100%. This sensor has a
50 mV span over the pressure range of interest. If the sensor were to experience an over-pressure event that took
the sensor output up to 90 mV (200% of span), the internal calculations could overflow. The result would be a
corrected bridge reading that would not be saturated at 100% as expected, but instead read a value lower than
100%. This problem only occurs when SOT is applied to correct the bridge reading.
As SOT applies to Tcg:
Resolution: 0.3 ppm/(
o
C)
2
Range: ±38 ppm/(
o
C)
2
As it applies to Tco:
Two settings are possible. It is possible to scale the effect of SOT by 8. If Tc_cfg[1] is set, then both, Tco and
SOT’s contribution to Tco, are multiplied by 8.
Resolution at unity scaling: 1.51 nV/V/(
o
C)
2
(input referred)
Range: ±0.192 mV/V/(
o
C)
2
(input referred)
Resolution at 8x scaling: 12.1 nV/V/(
o
C)
2
(input referred)
Range: ±1.54 mV/V/(
o
C)
2
(input referred)
Limitation: If the second order term SOT applies to Tco, the bridge gain Gain_B is limited to values equal or less
than 8 (instead of 64).
