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I am utilizing the Microchip TC1046VNBTR on my PCB to measure ambient temperature of the board. I am trying to get a reasonably accurate reading (2-3 °C accuracy). I am using a basic setup based on my past experience with temperature sensors, so I am using the following circuit, except with NO 2.2 kΩ resistor.

When I do, I get a 1 ms oscillation output on the IC with a 283 mV peak-to-peak ripple, which is MASSIVE for a temperature sensor. See below for the oscilloscope of the output (VOUT - Pin 3).

I am trying to figure out how to resolve this. 1ms time period on the ripple is quite large and 10 uF for an output capacitor is also quite significant for this application.

Does anyone know what causes this and what can be done to resolve it?

I verified that this ripple does NOT exist on the 3.3 V supply.

extract of schematic

photo of oscilloscope screen showing trace with oscillation

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  • \$\begingroup\$ 'Output Source and Sink Current' is limited to 100µA; could C85 have this much in leakage current? Lift C85 and replace with a smaller-value but higher-quality cap, like a C0G if possible. \$\endgroup\$
    – rdtsc
    Sep 20 at 20:12
  • \$\begingroup\$ 10 uF seems very high for a (I assume) smoothing capacitor, especially when the datasheet for the TC1046 doesn't specify any. Have you tried removing the capacitor entirely? Whatever smoothing you need can very likely be done in firmware. Is the ADC connected during your measurements? \$\endgroup\$
    – vir
    Sep 20 at 20:19

1 Answer 1

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Remove the cap on the output or add an R between the cap and the sensor.

When you add C to an amplifier output you can make it oscillate.

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