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TLV9002: NTC temperature sensor using TLV9002

Maheswari Arumugam
Prodigy 45 points
Part Number: TLV9002

Tool/software:

I am using a NTC in the range of 10ohm to 50K..I am expecting my output voltage in the range of 100mV to 3V. In a linear way 10 ohm means minimum 100mV and 50K should be limited to 3V. I tried with the below circuit design. But my output range is exceeding 3V and 10ohm is not 100mA. What changes I should to do limit it within 100mV for 10 ohm and  3V for 50K.  Help me with correcting my circuit. 

Resistive Sense 10 to 50K.TSC

  • 0
    TI__Genius 9655 points

    Hi Maheswari,

    What is the design goal here? I'm unsure what you mean by the 100mA being the output range. Do you want to map the NTC thermistor change from 10Ω to 50kΩ to an output voltage of 100mV to 3V at U1?

    I can readily see that U1 is used as a non-inverting amplifier, but what is the purpose behind U2's configuration? Why does U2 have positive feedback?

  • 0 in reply to HO SIU
    Prodigy 45 points

    Yes I want to map the NTC thermistor change from 10Ω to 50kΩ to an output voltage of 100mV to 3V at U1.

    I want constant current source for NTC . That is why I used U2. You can suggest a  changes in the circuit as per the goal. 

  • 0 in reply to Maheswari Arumugam
    TI__Genius 9655 points

    Hi Maheswari,

    Thanks for the clarification! I didn't catch that it was an Improved Howland Current Pump. The current was varying quite a bit, so I didn't immediately make the connection.

    I did a couple of changes:

    1. I increased the output impedance of the constant current source through increasing the resistance of the feedback paths so that the currents don't vary as much with the wide range of NTC magnitudes.

    2. I changed up the gain and introduced a DC offset to the non-inverting amplifier in order to change the output voltage to be within your range.

    Please let me know what you think.

    Resistive Sense 10 to 50K(3).TSC