MAX1450 データシートの表示（PDF） - Maxim Integrated

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MAX1450

Low-Cost, 1%-Accurate Signal Conditioner for Piezoresistive Sensors

Maxim Integrated 

MAX1450

Low-Cost, 1%-Accurate Signal Conditioner

for Piezoresistive Sensors

sensor evaluation. Note that the resistor values and PGA

gain obtained from this evaluation will represent a start-

ing point. The final compensated transducer will likely use

slightly different values. The required sensor information

is shown in Table 1, and can be used to obtain the values

for the parameters shown in Table 2.

Selecting RISRC

RISRC programs the nominal sensor excitation current

and is placed between ISRC and VSS. Use a variable

resistor with a nominal starting value of:

RISRC ≈ 13 x Rb(T1)

≈ 13(5kΩ)= 65kΩ

Selecting PGA Gain Setting

Calculate the ideal gain using the following formula, and

select the nearest gain setting from Table 3.

SensorFSO can be derived as follows:

SensorFSO= S × VBDRIVE × ∆P

= 1.5mV/V psi × 2.5V × 10 psi

= 0.0375V

where S is the sensor sensitivity at T1, VBDRIVE is the

sensor excitation voltage (initially 2.5V), and ΔP is the

maximum pressure differential.

where Rb(T1) is the sensor input impedance at tempera-

ture T1 (usually +25°C).

Selecting RSTC

RSTC compensates the FSO TC errors and is placed

between BBUF and ISRC. Use a variable resistor with a

nominal starting value of the following:

Table 1. Sensor Information

PARAMETER

Rb(T)

TCR

SENSOR DESCRIPTION

Input/Output Impedance

Input/Output Impedance

Tempco

TYPICAL

VALUE

5kΩ at +25°C

2600ppm/°C

R STC

≈

RISRC × 500ppm/°C

TCR − TCS

S(T)

≈

65kΩ × 500ppm/°C

TCS

= 65k Ω

2600ppm/ C − − 2100ppm/ C

O(T)

Sensitivity

Sensitivity Tempco

Offset

1.5mV/V psi at

+25°C

-2100ppm/°C

12mV/V at

+25°C

This approximation works best for bulk, micromachined,

silicon piezoresistive sensors (PRTs). Negative values

for RSTC indicate unexpected sensor behavior that can-

not be compensated by the MAX1450 without additional

external circuitry.

4.5

OTC

S(p)

PMIN

PMAX

Offset Tempco

Sensitivity Linearity Error

as % FSO BSLF (Best

Straight-Line Fit)

Minimum Input Pressure

Maximum Input Pressure

-1030 ppm-

FSO/°C

0.1% FSO

BSLF

0 PSI

10 PSI

Table 2.Compensation Components/Values

FULL-SPAN OUTPUT (FSO)

0.5

OFFSET

FULL-SCALE (FS)

PMIN

PMAX

PRESSURE

Figure 3. Typical Pressure-Sensor Output

PARAMETER

DESCRIPTION

RISRC

RSTC

APGA

OFFTC

RLIN

Resistor that programs the nominal sensor

excitation current

Resistor that compensates FSO TC errors

Programmable-gain amplifier gain

Offset TC correction voltage, including its

respective sign bit

Resistor that corrects FSO linearity errors

(optional)

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