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LM34 output flaky

Alvin P. Schmitt
Intellectual 940 points
Other Parts Discussed in Thread: LM34

When reading a lm34 from a microchip PIC16F1825 10 bit atod the readings were flaky - all over the place. I will ask microchip about this but does the analog output of the lm34 require a 0.1uf capacitor to keep the output stable? This is used to readout temperature in a hot/cold box for thermal stressing products. Had a 0.1uf from vdd to gnd for the lm34.

  • 0
    TI__Expert 7220 points
    Hi Alvin,

    How flaky is the output of the LM34 and what is your accuracy requirement? There is usually a bulk/filter capacitor between the output of an analog temperature sensor and the input of the ADC. This capacitor is used to dump charge directly into the internal sample capacitor in the ADC instead of relying on the output drive of the LM34. The size of this capacitor depends on a variety of factors such as sampling rate and the internal structure of the ADC. Is there a large capacitive load at the output of the LM34?

    -Michael Wong
  • 0 in reply to Michael Wong
    Intellectual 940 points

    There is a 0.1uf from vdd of the LM34 to gnd but no capacitor from Vout of the LM34 to gnd. Taking sample at one a second. No Cap load on Vout except for ADC input. Do I need a cap at Vout and what size?

  • 0 in reply to Alvin P. Schmitt
    TI__Expert 7220 points
    Hi Alvin,

    You can try adding a capacitor at the output, start with small sizes such as a 0.1nF. If you see reduced flakiness then a capacitor would be required .

    -Michael Wong