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LMT70: variable offset issue

Errol Leon6
Expert 5830 points
Part Number: LMT70

Hi team,

My customer is using the LMT70 in their design.  They are seeing a variable offset that appears on the LMT70YFQT output whenever we power cycle it. The offset is random and changes even when the unit is cycled quickly. The offset seems to persist and the output does not settle to the original value. THey feed the device from a 3.3 volt power supply which is derived from a switch mode supply, but with some filtering.

Is the LMT70YFQT susceptible to power supply noise or value?

Is the output susceptible to noise pick up or is it fairly low impedance?

Should the output have any filter capacitance on it?

Thank you in advance for your support!

Errol

  • 0
    TI__Mastermind 35855 points

    Hi Errol,

    The LMT70 datasheet is pretty comprehensive regarding the output. 

    Could I please see the power supply ramp and LMT70 output on oscilloscope?

    There is an output impedance spec of 80ohms, and it's only rated to drive around 5uA. It's not possible to put a high-current output on a temperature sensor, because it will cause temperature error from self-heating. 

    Output capacitance is not required for operation, but is encouraged for applications. Please note the spec table limits output capacitance to a max of 1.1nF, but Figure 25 shows how to add resistance to support larger capacitors.

    thanks,

    ren