Datasheet

LTC1966
31
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The calculations of the error terms for a 200mV full-scale
case are:
Gain =
Reading at 200mV – Reading at 20mV
180mV
Output Offset =
Reading at 20mV
Gain
–20mV
DC, 2 Point
DC based calibration is preferable in many cases because a
DC voltage of known, good accuracy is easier to generate
than such an AC calibration voltage. The only down side
is that the LTC1966 input offset voltage plays a role. It is
therefore suggested that a DC based calibration scheme
check at least two points: ±full-scale. Applying the –full-
scale input can be done by physically inverting the voltage
or by applying the same +full-scale input to the opposite
LTC1966 input.
For an otherwise AC-coupled application, only the gain
term may be worth correcting for, but for DC-coupled ap-
plications, the input offset voltage can also be calculated
and corrected for.
The calculations of the error terms for a 200mV full-scale
case are:
Gain =
Reading at 200mV +Reading at – 200mV
400mV
Input Offset =
Reading at – 200mV – Reading at 200mV
2•Gain
applicaTions inForMaTion
Note: Calculation of and correction for input offset voltage
are the only way in which the two LTC1966 inputs (IN1,
IN2) are distinguishable from each other. The calculation
above assumes the standard definition of offset; that a
positive offset is the case of a positive voltage error inside
the device that must be corrected by applying a like nega-
tive voltage outside. The offset is referred to whichever
pin is driven positive for the +full-scale reading.
DC, 3 Point
One more point is needed with a DC calibration scheme
to determine output offset voltage: +10% of full scale.
The calculation of the input offset is the same as for the
2-point calibration above, while the gain and output offset
are calculated for a 200mV full-scale case as:
Gain =
Reading at 200mV – Reading at 20mV
180mV
Output Offset =
Reading at 200mV +Reading at – 200mV – 400mV • Gain
2