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MAX1450

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

Maxim Integrated 

Low-Cost, 1%-Accurate Signal Conditioner

for Piezoresistive Sensors

sure sensor evaluation. Note that the resistor values

and PGA gain obtained from this evaluation will repre-

sent a starting point. The final compensated transducer

will likely use slightly different values. The required sen-

sor 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

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

ature 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:

R STC

≈

RISRC x 500ppm/°C

TCR − TCS

≈

65kΩ x 500ppm/°C

= 65kΩ

2600ppm/ oC − − 2100ppm/ oC

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 addition-

al external circuitry.

4.5

FULL-SPAN OUTPUT (FSO)

0.5

OFFSET

FULL-SCALE (FS)

PMIN

PMAX

PRESSURE

Figure 3. Typical Pressure-Sensor Output

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 x VBDRIVE x ∆P

= 1.5mV/V psi x 2.5V x 10 psi

= 0.0375V

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

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

maximum pressure differential.

Table 1. Sensor Information

PARAMETER

SENSOR

DESCRIPTION

TYPICAL

VALUE

Rb(T)

Input/Output Impedance 5kΩ at +25°C

TCR

Input/Output Impedance

Tempco

2600ppm/°C

S(T)

Sensitivity

1.5mV/V psi at

+25°C

TCS

Sensitivity Tempco

-2100ppm/°C

O(T)

Offset

12mV/V at

+25°C

OTC

S(p)

Offset Tempco

-1030 ppm-

FSO/°C

Sensitivity Linearity Error as

% FSO BSLF (Best Straight-

Line Fit)

0.1% FSO

BSLF

PMIN

Minimum Input Pressure

0 PSI

PMAX

Maximum Input Pressure 10 PSI

Table 2. Compensation Components/Values

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)

6 _______________________________________________________________________________________

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