AK8996 Datasheet, PDF (39/74 Pages) Asahi Kasei Microsystems – Pressure Sensor Interface IC

[AK8996/W]
12. Output Span Voltage Fine Adjustment
Adjusts the error caused when the sensitivity temperature drift is compensated for. The output span
voltage is adjusted using the output span voltage adjustment register (Address: 02h data ESC[8],
address: 03h data ESC[7:0]).
2) Finding the VO Pin External Capacitance (Cap)
This section explains how the VO pin external capacitance is defined. The requirements for
determining the VO pin external capacitance value are, the stabilization time of the VOUT pin output
voltage on power-up and after exiting the standby mode (STBYN pin "L" to "H") and SINAD
(Signal/[Noise + Distortion]).
1. VOUT Pin Output Voltage Stabilization Time
Note that depending on the VO pin external capacitance values, the measurement values (VOUT pin
voltage) may contain errors upon power-up or after exiting STBYN. Stabilization time is not dependent
on the sampling clock.
Here is an example with the aid of a diagram and tables. "99.5% Settling time ( + in the figure)" in
the table below represents the time required for the voltage to settle to the output reference voltage X
(0.5*VDD in this case) during the period in the figure and the voltage to settle down to 99.5% of the
output voltage Y (0.1*VDD in this case) according to the pressure applied during the period ( + in
the figure). ^Note)
Under the conditions where the VO pin has an external capacitance of 3µF (sampling frequency
100Hz), the VOUT pin voltage will settle down to 16.4% (0.0815*VDD with respect to the expected
0.5*VDD value) of the output reference voltage during the period in the figure. The period in the
figure is fixed to 0.3 msec.
Settling factor A=(1-e^(-0.3[msec]/(560[Ω]*3[µF]))*100=16.4[%]
Subsequently, the output voltage will settle to 99.5% according to the pressure during period in the
figure. During period in the figure below, the output will settle down to from 0.0815*VDD to 99.5% of
0.1*VDD in 345.2 msec.
Settling factor B=(0.995*0.1*VDD-0.164*0.5*VDD)/(0.1*VDD-0.164*0.5*VDD)*100=97.2[%]
Settling time D (period in the figure) =-32[kΩ]*3[µF]*ln(1-B/100)=345.2 [msec]
Therefore, the settling time up to 99.5% (period + in the figure) will be as follows:
99.5% settling time (period + in the figure) = 0.3 [msec] + D = 345.5 [msec]
MS1055-E-02
39
2011/12