Design Information

T: Temperature
V_out(T): Output voltage as a function of temperature
V_PTC(T): Voltage divider output voltage as a function of temperature. The voltage range of V_PTC(T) should not violate the input common mode range of the amplifier
R_PTC(T): Resistance of the PTC as a function of temperature
V_bias: Voltage source connected to PTC.

Equation 1.

V_{o u t} (T) = V_{P T C} (T) \times (1 + R 4 \times (\frac{R 3 + R 5}{R 3 \times R 5})) - V_{b i a s} \times (\frac{R 4}{R 5})

Note: For this example the TMP61 10-kΩ Linear Thermistor is utilized.

Equation 1.

V_{P T C} (T) = V_{b i a s} \times (\frac{R_{P T C} (T)}{R_{P T C} (T) + R 1})

Equation 1.

R_{P T C} (T) = A_{4} (T^{4}) + A_{3} (T^{3}) + A_{2} (T^{2}) + A_{1} (T) + A_{0}

The constants A₄–A₀ can be derived from the TMP61 design tools for voltage dividers using a given V_bias and R_bias. More information is found in the Thermistor Design Tool (SBOC595).