AK8996 Datasheet, PDF (37/74 Pages) Asahi Kasei Microsystems – Pressure Sensor Interface IC

[AK8996/W]
■ Sensitivity Temperature Secondary Characteristics Calculation Example (See 5) Register
Description in the "Serial Interface Description" section)
Assume the AK8996's secondary characteristics (quadratic function and linear function) as:
Vic=[(g*a)T^2+(g*b)T+(g*c)]+[dT+e]=(g*a)T^2+(g*b+d)T+(g*c+e)
Quadratic function Linear function
For example, the content of the adjustment register corresponds to the sensor's secondary
characteristic in the positive pressure is measured by:
Assume the secondary characteristic of the measured sensor is Vsen = 0.00051T^2 - 0.2345T + 0.0.
If the secondary characteristic of the measured AK8996's sensitivity temperature is Vic2=0.0016T^2
- 0.16T + 0.0 and the primary characteristic is Vic1=0.32T + 0.0, set the coefficient to match the
sensor's secondary characteristic (i.e., AK8996's secondary characteristic becomes Vic=
0.00051T^2 - 0.2345T + 0.0).
ST2P[7]: Second-order coefficient adjustment sign bit for the sensitivity temperature secondary
characteristics
Set EST2P[7]=0 to make the measured AK8996's second-order coefficient (g*a)
positive.
Set EST2P[7]=1 to make the measured AK8996's second-order coefficient (g*a)
negative.
In this example, set "0" because the second-order coefficient (g*a) is 0.00051.
ST2P[6:0]: Coefficient adjustment bit for sensitivity temperature secondary characteristics
Adjust the coefficient in 0.7874% steps.
For example, set EST2P[6:0]=123dec and g*a=0.0005039 for the measured AK8996's
second-order coefficient (g*a). That is, the AK8996's secondary characteristic is Vic2
= 0.0005039T^2 - 0.05039T + 0.0.
0.0005039=0.0016*|1-0.7874/100*123|
0.05039=0.16*|1-0.7874/100*123|
Next, adjust the first-order coefficient so that the AK8996's first-order coefficient (g*b + d) equals
-0.2345.
ST1P[9]: First-order coefficient adjustment sign bit for the sensitivity temperature secondary
characteristics
Set EST1P[9]=0 if the adjustment first-order coefficient d is for addition.
Set EST1P[9]=1 if the adjustment first-order coefficient d is for subtraction.
In this example, set "1" because the first-order coefficient (g*b + d) is subtracted from
-0.05039 after secondary characteristics adjustment.
ST1P[8:0] : First-order coefficient adjustment bit for the sensitivity temperature secondary
characteristics
Since a first-order coefficient is -0.2345 (=-0.05039-0.18411), set EST1P[8:0]=354dec
and d=-0.18434. That is, the AK8996's primary characteristic is Vic1=-0.18434T+0.0.
Now the adjustment of the second-order and first-order coefficients is completed with the
adjustment (Vic=0.00051T^2-0.2345T+0.0). The zero order coefficient is, ideally, 0.0, but it could
remain as a span voltage. If that is the case, fine-tune according to the span voltage adjustment
procedure after finishing the offset and sensitivity temperature drift adjustment.
MS1055-E-02
37
2011/12