AK8998 Datasheet, PDF (7/59 Pages) Asahi Kasei Microsystems – Preliminary

[AK8998/W/D]
Description of Blocks
[Gain Amplifier Block, LPF, S/H&SCF& Level shifter, Buffer&SMF]
The set of these blocks amplifies, compensates and outputs the pressure sensor level
This set of blocks intermittently amplifies, compensates, samples and holds the pressure sensor
output. The output stage, with an internal resistor of 146kΩ, is band-limited with a combination of
external capacitors, providing a low impedance output. SCF and SMF are available for output,
eliminating the need for the external capacitors. A percentage designator is used, benchmarked
with 4800mVdc output at 100%, reflecting the 60x increase in differential input from 80mVdc.
Block
Functions
Gain Amp.1 is a low-noise high-gain amplifier at the front end. The differential
signal is amplified by a factor of 10x typ. (5x to 70x).
Gain Amp.2 converts the G1 differential output to single-ended with reference to
Gain Amp.
1/2/3
Gain
(G1/2/3)
AGND and amplifies by a factor of 1.5x typ. (1.5x or 3.0x) or 1.176x typ. (1.176x or
2.352x).
Gain Amp.3 amplifies by a factor of 1.8x typ. (1.1x to 1.8x) or 2.3x typ. (1.4x to
2.3x).
G2 gain and G3 gain are changed automatically by sensitivity temperature drift
adjustment range change setup (ESTC [0]).
Span voltage is adjusted with G1/2/3 Gain (G1/2: rough adjustment, G3: fine
adjustment).
The preloaded compensation data in the EEPROM enables the pressure sensor
Offset_Temp. offset voltage and offset temperature drift to be compensated. The following
Offset
adjustment value is AK8998 input conversion @5.0V.
Offset Temp. Offset adj.Adj. range Rough ±13 to ±373mV / Fine ±1 to ±34mV
track
Adj. step Rough 2 to 53mV /step / Fine 0.01 to 0.27mV /step
(G2)
Offset temp. drift. adj. Adj. range ±0.04 to ±1.23mV/ ºC
Adj. step 0.2 to 4.8µV/ºC step
Supply voltage and sensitivity temperature variation compensation circuit.
Monitors the AGND voltage to calculate the magnitude of supply voltage variation;
STV
VDD track
Gain_Temp.
(STV)
the pressure sensor sensitivity temperature drift is calculated for entry into G3
using the temperature sensor output voltage and preloaded compensation data
(EEPROM data). The sensitivity temperature drift adjustment range can be
changed by EEPROM data (ESTC[0]).
Sensitivity temp. drift. adj. Adj. range -4000ppm/ ºC to +2500ppm/ ºC
or -2500ppm/ ºC to +1000ppm/ ºC
Adj. step 18ppm/ ºC step
Anti-aliasing filter to eliminate the fold-back noise generated in the
LPF
sample-and-hold circuit (S/H) in the later stage. The cutoff frequency is fc=60kHz.
S/H &
Level Shift
& SCF
Buffer
& SMF
S/H doubles the LPF output and samples and holds it. The output reference voltage
can be changed.
Output reference voltage adj. Adj. range 0.02*VDD to 0.98*VD
Adj. step 0.002*VDD /step
SCF is a low-pass filter used for internal band limiting without using the external
capacitors. The cutoff frequency (fc: 1kHz /500Hz /250Hz) of the filter can be set by
EEPROM.
Buffer to produce a band-limited output with low impedance. Provides 1.111x
output. 146kΩ internal resistance and an external capacitor (C) make the LPF
characteristics. Change the external capacitance value according to the desired
signal band for detection using the following equation:
fc=1/(2*π* 146kΩ*C) (Hz)
SMF is a low-pass filter (fc=10kHz) used for eliminating the clock noise produced
by the SCF in the previous stage. SMF is switched on or off in combination with the
previous-stage SCF using the EEPROM data.
MSxxxxx-E-00
-7-
2012/11