AK8996 Datasheet, PDF (38/74 Pages) Asahi Kasei Microsystems – Pressure Sensor Interface IC

[AK8996/W]
9. Offset Voltage Fine Adjustment
Adjusts the error caused when the offset voltage temperature drift are compensated for. Offset voltage
is adjusted using the offset voltage rough adjustment register (Address: 00h data EOC[10:7]) and
offset voltage fine adjustment register (Address: 01h data EOC[6:0]).
10. BUFF Gain Adjustment
Adjusts the output buffer gain. The output buffer gain is adjusted using the BUF gain adjustment
register (Address: 0Eh data EOG[2:0]).
11. Pressure Determination Threshold and Output Reference Voltage Adjustment
Specific adjustment procedures for the output reference voltage are shown based on this block
diagram.
S/H1 &
Level Shifter
ELV[10:6]
ELV[5:0]
S/H2
32kohm
EOG[2:0]
Buffer
EPJLV[9:0]
Pressure
judge
VO
VOUT
Adjust the pressure determination threshold values (adjust the pressure determination threshold
value first, followed by the output reference voltage). Pressure determination threshold values are
adjusted using the pressure judgment threshold adjustment registers 1 and 2 (Address: 1D, 1Eh data:
EPJLV[9:0]).
As shown in the diagram, the buffer circuit and pressure judgment circuit are tuned for the pressure
determination threshold adjustments. Thus, the VO pin voltage after the pressure determination
threshold adjustment is almost equal to 2.5V (@VDD: 5V) as a result of the offset voltage adjustment
in Section 5. So, after adjusting the pressure determination threshold, some pressure determination
threshold values may cause the VOUT pin voltage to get stuck at the supply voltage. For example, if
the pressure determination threshold is adjusted to 1.0V with a supply voltage of 5V EOG[2:0]=4hex
(set to 4x), the VOUT pin voltage is 1.0 + 4*(2.5 - 1.0) = 7.0V, stuck at the supply voltage.
Adjust the output reference voltage. The output reference voltage is adjusted using the register for the
output reference voltage’s rough and fine adjustments (Address: 1B, 1Ch data: ELV[10:0]).
First, calculate the adjustment value for the output reference voltage rough adjustment (ELV[10:6]).
Specifically, since it is known that the VO pin voltage is 2.5V (@VDD: 5V) and the buffer reference
voltage is the pressure determination threshold, calculate so that the difference between the two
values is as small as possible. Next, adjust the VOUT pin voltage to the desired output reference
voltage using the output reference voltage fine adjustment (ELV[5:0]).
MS1055-E-02
38
2011/12