AK8996 Datasheet, PDF (6/74 Pages) Asahi Kasei Microsystems – Pressure Sensor Interface IC

[AK8996/W]
Description of Blocks
Gain Amplifier Block, LPF & S/H1 & Level Shifter, S/H2 & Buffer
The set of these blocks amplifies, compensates and outputs the pressure sensor level with a
normal gain ratio of 50:1. This set of blocks intermittently amplifies, compensates, samples and
holds the pressure sensor output. The output stage, with an internal resistor of 32kΩ, is band-limited
with a combination of external capacitors, providing a low impedance output through a buffer. A
percentage designator is used, benchmarked with 4000mVdc output at 100%, reflecting the 50x increase
in differential input from 80mVdc.
Block
Gain Amp. 1
(G1)
Gain Amp. 2
Offset_Temp.
Offset
Offset Temp.
track
(G2)
Gain Amp. 3
Gain_Temp.
Gain
(G3)
STV
VDD track
Gain Temp.
track
(STV)
Pressure
Judge
LPF
Functions
A low-noise high-gain amplifier at the front end. The differential signal is increased
by a factor of 5 (typically) (with factors of 2 to 9, in single-factor steps).
The G1 differential output is converted to single-ended with reference to AGND
and typically amplified by a factor of 1 (1 or 2). The preloaded compensation data
in the EEPROM enables the pressure sensor offset voltage and offset temperature
secondary characteristics to be compensated.
Offset adj. Resolution: Rough: 4-bits; Fine: 7-bits
Adj. step: Rough: 7.5%; Fine: 0.125% @VDD: 5V
Offset temp. drift.Resolution: 1^st order coeff: 10-bits; 2^nd order coeff: 8-bits
Adj. step: 1^st order coeff: 0.196%; 2^nd order coeff: 0.787%
Amplifies the G2 output by a factor of 1.25 (typically). The preloaded compensation
data in the EEPROM enables the pressure sensor span voltage and sensitivity
temperature secondary characteristics to be compensated.
Span adj. Resolution: 9-bits
Adj. value: 100/[100+0.25*N](%) N: -256 to +255
Supply voltage and sensitivity temperature variation compensation circuit.
Monitors the AGND voltage to detect the magnitude of supply voltage variation; the
pressure sensor sensitivity temperature secondary characteristics compensation
values are calculated for entry into G3 using the temperature sensor output voltage
and preloaded compensation data (EEPROM data).
Sensitivity temperature drift
Resolution: 1^st order coeff: 10-bits; 2^nd order coeff: 8-bits
Adj. step: 1^st order coeff: 0.196%; 2^nd order coeff: 0.787%
Compares the pressure sensor VOUT pin output voltage to the threshold voltage to
define the sensitivity temperature secondary characteristics compensation
coefficient.
Pressure determination threshold adj. Resolution: 10-bits
Adj. step: 0.001*VDD (0.05*VDD – 0.95*VDD)
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 external capacitance value of the VO pin.
When the VOUT pin output voltage is more than the output reference voltage, the
positive (+) sensitivity temperature secondary characteristic compensation
coefficient is selected; but when the VOUT pin output voltage is less than the
output reference voltage, the negative (-) sensitivity temperature secondary
characteristic compensation coefficient is selected.
Note) If the output reference voltage is half of VDD, pressure threshold adjustment
is unnecessary. Even if the compensation coefficient +/- is not used,
pressure threshold adjustment is required if the output reference voltage is
set to a value other than half of VDD.
Anti-aliasing filter to eliminate the fold-back noise generated in the
sample-and-hold circuit (S/H 1&2) in the later stage. The cutoff frequency is
fc=60kHz.
MS1055-E-02
6
2011/12