MAX1450 查看數據表（PDF） - Maxim Integrated
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MAX1450 Datasheet PDF : 12 Pages
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MAX1450
Low-Cost, 1%-Accurate Signal Conditioner
for Piezoresistive Sensors
Table 3. PGA Gain Settings
PGA GAIN (V/V) PGA VALUE A2 A1 A0
39
0
0
0
0
65
1
0
0
1
91
2
0
1
0
117
3
0
1
1
Select the Offset TC resistor divider (ROTCA and ROTCB,
Figure 4) using the following equation:
OTC Correction =
R OTCA
R OTCA + R OTCB
0.17 =
R OTCA
R OTCA + R OTCB
143
4
1
0
0
where 500kΩ ≥ (ROTCA + ROTCB) ≥ 100kΩ. Choose
169
5
1
0
1
ROTCB = 100kΩ and ROTCA = 20kΩ.
195
6
1
1
0
221
7
1
1
1
A PGA
≈
OUTFSO
SensorFSO
≈ 4V = 106V/V
0.0375V
where OUTFSO is the desired calibrated transducer full-
span output voltage, and SensorFSO is the sensor full-
span output voltage at T1.
Determining OFFTC Initial Value
Generally, the OFFTC coefficient can be set to 0V, since
the offset TC errors will be compensated in a later step.
However, sensors with large offset TC errors may require
an initial coarse offset TC adjustment to prevent the PGA
from saturating as the temperature increases during
the compensation procedure. An initial coarse offset TC
adjustment would be required if the magnitude of the sen-
sor offset TC error is more than about 10% of the FSO.
If a coarse offset TC adjustment is required, use the fol-
lowing equation:
OTC Correction =
∆VOUT(T)
∆VBDRIVE(T) × 1.15
Transfer Function
The following transfer function (linearity correction not
included) is useful for data modeling or for developing
compensative algorithms:
= VOUT VBDRIVE ×
VS
×
PGA
+
1.15
×
V OFFTC
VDD
+
1.15 x
VOFFSET
VDD + VDD
where VBDRIVE =
RISRC
1
R STC
+1
AA x Rb(T) R STC
(AA = current source gain)
FSO Calibration
Perform FSO calibration at room temperature with a fulls-
cale sensor excitation.
1) At +25°C (or T1), set VFSOTRIM to 2.5V. Adjust RISRC
until VBBUF = 2.5V.
2) Adjust VOFFSET until the room temperature offset volt-
age is 0.5V (see OFFSET Calibration section).
3) Measure the full-span output (measuredVFSO).
4) Calculate VBIDEAL(25°C) using the following equation:
whichOcTaCnCboerraepcptiroonxim≈≈aT−te1C0dS3b0×OypV:TpBCmD×/RF°ICVSEO××4x1V(.1∆= 5T)×0(.6∆8T) VVFBSIDOETARLI(M251C+)
=
desiredVmFSeaOsu−remdVeaFsSuOredVFSO
−2100 × 2.5V ×1.15
where OTC is the sensor offset TC error in ppm of FSO,
ΔT is the operating temperature range in °C, and OTC
Correction is the offset TC resistor-divider ratio. For posi-
Note: If VBIDEAL(25°C) is outside the allowable bridge volt-
age swing of (VSS + 1.3V) to (VDD - 1.3V), readjust the
PGA gain setting. If VBIDEAL(25°C) is too low, decrease
the PGA gain setting by one step and return to Step 1. If
tive values of OTC correction, connect SOTC to VDD; for
negative values, connect SOTC to VSS.
VBIDEAL(25°C) is too high, increase the PGA gain setting
by one step and return to Step 1.
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