AK8998 Datasheet, PDF (30/59 Pages) Asahi Kasei Microsystems – Preliminary

[AK8998/W/D]
6. Offset Voltage Adjustment
The offset voltage for the pressure sensor is adjusted including the AK8998 internal error by using
the offset voltage adjustment EEPROM (address:00, 01h data:EOCR[3:0], EOCF[7:0]).
■Offset Voltage Adjustment Example (@VDD:5V)
EOCR[3]: Offset voltage rough adjustment sign bit
If unadjusted output is more than 0.5*VDD, set EOCR[3]=1h.
If unadjusted output is less than 0.5*VDD, set EOCR[3]=0h.
EOCR[2:0]: Offset voltage rough adjustment: Adjust in 1600-mV steps.
EOCF[7]: Offset voltage fine adjustment sign bit
If unadjusted output is more than 0.5*VDD, set EOCF[7]=1h.
If unadjusted output is less than 0.5*VDD, set EOCF[7]=0h.
EOCF[6:0]: Offset voltage fine adjustment: Adjust in 8-mV steps.
When the offset voltage is +360mV (0.5*VDD reference), set EOCF[7]=1h and
EOCF[6:0]=45dec.
360[mV]-(8[mV]*45[dec])=0.0[mV]
7. Input gain (G1/G2) setup
Set up G1/G2 gain so that Gain Amp.1/2 output voltages become the ranges (In the case of
VDD=5V, G1≤ 1700mV, G2≤ 1950mV). The voltage and temperature coefficient which are
used for calculation is as follows.
The offset voltage and the span voltage in 25 °C are calculated by dividing the measurement result
(VOUT pin) of the 1st offset voltage and the Span voltage by 18.35 (total gain). And for the offset
voltage temperature drift coefficient and the sensitivity temperature drift coefficient, the MIN value
(minus polarity) of the pressure sensor assumed is used.
In addition, since offset voltage and the offset voltage temperature drift coefficient are adjusted
with Gain Amp.1 output, G2 gain is calculated noting that only the Span voltage and the sensitivity
temperature drift coefficient.
Voff25: Offset voltage of the pressure sensor@25°C
Vsp25: Span voltage of the pressure sensor @25°C
Ktoff: Offset voltage temperature drift coefficient of the pressure sensor (MIN value)
Ktsp: Sensitivity temperature drift coefficient of the pressure sensor (MIN value)
■ In the case of VDD=5V and temperature=-20 to 85°C
Gain Amp.1 output
=G1*(Voff25+Vsp25+ktoff*(-20[°C]-25[°C])+Vsp25*ktsp*(-20[°C]-25[°C])) ≤ 1700mV
Gain Amp.2 output
=G1*G2*(Vsp25+Vsp25*ktsp*(-20[°C]-25[°C])) ≤ 2100mV
■ In the case of VDD=3.3V/3.0V and temperature=-20 to 85°C
Gain Amp.1 output
=G1*(Voff25+Vsp25+ktoff*(-20[°C]-25[°C])+Vsp25*ktsp*(-20[°C]-25[°C])) ≤ 800mV/800mV
Gain Amp.2 output
=G1*G2*(Vsp25+Vsp25*ktsp*(-20[°C]-25[°C])) ≤ 1250mV/1150mV
8. Offset Voltage Readjustment
The offset voltage is readjusted.
The offset voltage adjustment EEPROM is once reset to ALL"0", and the adjustment should be
done again using the offset voltage adjustment EEPROM.
MSxxxxx-E-00
- 29 -
2012/11