AK8996 Datasheet, PDF (36/74 Pages) Asahi Kasei Microsystems – Pressure Sensor Interface IC

[AK8996/W]
Specific calculation examples are described here.
■ Offset Temperature Secondary Characteristics Calculation Example (See 5) Register Description in
"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 contents of an adjustment register corresponding to the sensor's secondary
characteristics is measured by:
Assume the secondary characteristic of the measured sensor is Vsen = 0.0003T^2 - 0.0237T+ 0.0.
If the temperature secondary characteristic of the measured AK8996's offset voltage is
Vic2=0.0016T^2 - 0.16T + 0.0 and the primary characteristic is Vic1=0.6T + 0.0, set the coefficient
so that the sensor's secondary characteristic is canceled out (i.e., AK8996's secondary
characteristic becomes Vic=-0.0003T^2 + 0.0237T - 0.0).
EOT2[7]: Second-order coefficient adjustment sign bit for the offset voltage temperature drift
To make the measured AK8996's second-order coefficient (g*a) positive, EOT[7]=0.
To make the measured AK8996's second-order coefficient (g*a) negative, EOT[7]=1.
In this example, set "1" because the second-order coefficient (g*a) is -0.0003.
EOT2[6:0]: Second-order coefficient adjustment bit for the offset voltage temperature drift
Adjust the coefficient in 0.7874% steps.
For example, set EOT2[6:0]=103dec and g*a=-0.000302 for the measured AK8996's
second-order coefficient (g*a). That is, the AK8996's secondary characteristic is
Vic2=-0.000302T^2 + 0.0302T - 0.0.
0.000302=0.0016*|1-0.7874/100*103|
0.0302=0.16*|1-0.7874/100*103|
Next, adjust the first-order coefficient so that the AK8996's first-order coefficient (g*b + d) equals
+0.0237.
EOT1[9]: First-order coefficient adjustment sign bit for the offset voltage temperature drift
Set EOT[9]=0 if the adjustment first-order coefficient d is for addition.
Set EOT[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
+0.0302 after secondary characteristic adjustment.
EOT1[8:0]: First-order coefficient adjustment bit for the offset voltage temperature drift
Since the first-order coefficient is +0.0237 (=0.0302-0.0065), set EOT1[8:0]=456dec
and d=-0.00646. That is, the AK8996's primary characteristic is Vic1=-0.00646T+0.0.
0.00646=0.6*|1-0.1957/100*456|
Now the adjustment of the second-order and first-order coefficients is completed with the
adjustment (Vic=0.0003T^2-0.0237T+0.0). The zero order coefficient is, ideally, 0.0, but it could
remain as an offset voltage. If that is the case, fine-tune according to the offset voltage fine
adjustment procedure after finishing the offset and sensitivity temperature drift adjustment.
MS1055-E-02
36
2011/12