AK8996 Datasheet, PDF (42/74 Pages) Asahi Kasei Microsystems – Pressure Sensor Interface IC

[AK8996/W]
3) Pressure Detection & Determination Circuit Operation at Power-Up and Standby Exit (STBYN pin
"L" to "H")
Use caution when operating the pressure detection and pressure determination circuits on power-up
and after exiting the standby mode (STBYN pin "L" to "H").
1. Pressure detection circuit operation
For proper operation of the pressure detection circuit, it is necessary to settle the VOUT pin output
voltage to within ±0.5% of the output reference voltage configured in the "Settling time for stable
analog operation" (See "Operation Sequence" Section).
The VOUT pin output voltage settles in the time constant determined by the 32kΩ internal resistance
and VO pin external capacitance. To understand settling time, see 2) Finding the VO pin external
capacitance (Cap). If the Cap value is 0.1µF or less, the VOUT pin output voltage settles to within
±0.5% of the output reference voltage, while with the use of capacitance greater than 0.1µF, errors
may be detected because it does not settle to within ±0.5%.
In order to avoid this problem, the pressure detector should be left disabled for a short time at
power-up and at exiting the STBYN mode. Calculate the disable time based on 2) Finding the VO pin
external capacitance (Cap). There is a simplified equation to determine the worst-case value:
Disable time = -39400[Ω] * 1.1*C[F] |* ln (1-0.995)
2. Pressure Detection Circuit Disable Time
Pressure detection circuit Disable time is the time from exit of the settling time for stable analog
operation to the pressure detection output. Pressure detection circuit Disable time with
pressure detection valid and both pressure detection and self-diagnosis valid is shown below.
2.1 Pressure detection valid (EINT1[1:0]=1h)
EAS[2: 0]
Dec Hex Bin
0 0 000
1 1 001
2 2 010
3 3 011
4 4 100
5 5 101
6 6 110
7 7 111
Pressure Detector Disable Time (msec)
fs: 100Hz fs: 1kHz fs: 2kHz fs: 10kHz
10
1.0
0.5
0.1
10
1.0
0.5
0.2
20
2.0
1.0
0.4
60
6.0
3.0
0.8
140
14.0
7.0
1.6
300
30.0
15.0
3.1
620
62.0
31.0
6.3
1260
126.0
63.0
12.5
Comments
Default
VDD
Settling time for
stable analog operation
DET pin output
MS1055-E-02
Pressure detector disable time
42
2011/12