AK8996 Datasheet, PDF (7/74 Pages) Asahi Kasei Microsystems – Pressure Sensor Interface IC

[AK8996/W]
Block
S/H1&
Level shift
S/H2
Buffer
Timing
Logic
Regulator
Pressure
Detector
Functions
Doubles the LPF output for the sample and hold. It also modifies the output
reference voltage.
Output ref. voltage adj. Resolution: Rough: 5-bits; Fine: 6-bits
Adj. step: 0.0005*VDD (0.0785*VDD – 0.9215*VDD)
Description is with reference to VO pin.
Note) If the output reference voltage is half of VDD, output reference voltage adjustment is
unnecessary.
Sample-and-hold circuit.
A 32kΩ resistor is connected to the output stage. The combination with an external
capacitor creates the LPF characteristics.
Change the external capacitance value according to the desired signal band for
detection using the following equation:
fc=1/(2*π*32kΩ*C) (Hz)
If the application does not require a low-impedance output, the VO pin output can
be used as an alternative. In this case, set the EEPROM data to disable the buffer.
Disabling the buffer allows for lower power dissipation. However, since the VO pin
has a 32kΩ output impedance, connecting a resistive load will cause output
voltage inaccuracies. Note also that the gain retained in the buffer cannot be
achieved.
Buffer to produce a band-limited output with low impedance. Typically provides a
fourfold output (2x to 4x, in 0.5 steps).
Reprogramming the EEPROM allows the buffer to be disabled for low power
dissipation. (See S/H2.)
Generates timing sync signals for internal operation and sampling frequencies for
sensor output signals. Sampling frequencies can be selected from the EEPROM.
Sampling frequency (fs): 100Hz (default); 1 kHz; 2kHz; 10.24kHz
Constant voltage generator circuit to drive the sensor. The drive voltage can be
selected from the EEPROM depending on the supply voltage being used.
Drive voltage: 4.0V @VDD: 5V±10% (default); 2.0V @VDD: 2.2 to 3.6V
Pressure detection circuit and self-diagnosis circuit.
The pressure range can be selected depending on the EEPROM data for the pressure
detector.
• Pressure above a certain value is detected (determined by threshold).
• Pressure below a certain value is detected (determined by inverted threshold).
• Pressure above or below a certain value is detected (determined both by a
threshold and an inverted threshold).
The DET pin goes high when the detected pressure exceeds the threshold. The
detection threshold value can be set by entering it via the PTH pin or using the EEPROM
data in the AK8996. Note that upon powering up and exiting standby (STBYN pin from
low to high) the precise pressure cannot be determined until the VOUT pin output settles,
depending on the setup and external capacitance value of the VO pin.
The self-diagnostic circuit ensures that the output (VOUT pin) produces a given value by
fixing the VP and VN pins at half of VDD upon power-up, or only at initial operation
immediately after exiting the standby mode. In the event of any anomalies, signals go
high at the DET pin. To reset the self-diagnostic circuit, set the STBYN low or recycle the
power. Bear in mind that the self-diagnostic circuit does not detect all of the failure
modes of the AK8996.
MS1055-E-02
7
2011/12