ST STM32373C-EVAL User Manual page 27

UM1564
The operational amplifier differential input voltage provided by the pressure sensor is given
in Equation
Equation 10
V – V
IN+ IN-
Where:
●
P = the pressure measured
m
●
K = sensitivity of the sensor (40 mV for VDD = 10 V and 1000 HPa)
The ADC output is related to the differential voltage by
Equation 11
V
=
ADC
where:
●
N is the value returned by the ADC corresponding to the pressure measured
● V
ref_ADC
●
G
ADC
So, if V
ref_ADC
Equation 12
16
⁄ (
N 2
Conclusion
1. When the ADC external reference voltage is selected and JP17 jumper is closed,
V
ref_ADC
2. The R2/R3 term in
corresponding to atmospheric pressure to be partially reduced. Consequently, the
digital gain can be increased to improve sensitivity.
Note: V may be used to compensate the temperature sensor drift by measuring the sensor
TEMP
current change with temperature.
10.
× ×
= P K VDD
m
16
× ⁄ ( )
V N 2 1
–
ref_ADC
is the ADC reference voltage (SD_VREF+ in
is the ADC digital gain
= VDD Equation 11
) [ × × (
– 1 = P K G +
m
= VDD so the pressure measurement becomes VDD independent.
Equation 11
Doc ID 023566 Rev 1
[ × × × (
P K VDD G
=
m
becomes Equation
⁄ ) R2 ⁄ ] ×
R2 R3 – R3
and Equation 12
Hardware layout and configuration
Equation 11.
⁄ ) VDD ×
R2 R3 R2
+ –
Figure 26)
12.
G
ADC
allows the offset voltage
⁄ ] ×
R3 G
ADC
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