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TMP275: Temperature reading sensitivity to power supply noise

Yuval Yunger
Prodigy 10 points
Part Number: TMP275
Other Parts Discussed in Thread: TPS82130

We have a few TMP275 sensors spread around in a system, connected by wires, and powered by a 5v TPS82130 (powering also some other relatively light loads).

What should be the 5v PS specifications (noise/ripple), to get reliable repeatable measurements ? 

The reason for asking:

  • On all systems, when changing system modes, we have significant temperature reading jump (often 1-1.5 degrees, sometimes more).
  • On some systems we encounter sensors providing noisy readings.

The source for (at least the jumps):

  • Reading jumps come from the 5v supply (can be improved or eliminated by manipulations of the 5v supply (e.g. connecting another PS, filtering, loading).
  • Probing the 5v we see some ripple/noise which is originally about 150 mv (and may very slightly change for different system modes) .

DS does say accuracy is 1.5 degrees for 3.3 - 5.5v supply, but also specify repeatability of 0.06 degrees. there is no PSRR data in the DS.

  • 0
    TI__Mastermind 40875 points

    Hi Yuval,

    The Temperature Error vs Supply (PSR) spec for TMP275 should be 0.2C/V typical. I'm not sure why it was omitted from the datasheet. 

    However, this spec is for DC voltage change. It does not account for noise which has a voltage change-in-time (AC) component. We don't have a noise test or spec on other temperature sensors. I would point out that any IC should have a typical 0.1uF or 0.01uF bypass capacitor near its supply pins. There is a bypass capacitor shown in our TMP275 datasheet Figure 16. If this capacitor is not able to prevent the the supply voltage from sagging below the minimum operating voltage of 2.7V for a microsecond, there is a risk of corrupting the operation of TMP275.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 10 points

    Thanks Ren!

    There is 0.1uF capacitor near each sensor and the noise level is less than 0.2v (so for 5v, PS is far above 2.7v min requirement), still we see the reading jumps, so seem the AC noise effect is much more than the DC figure of 0.2C/V.

    Does the TMP275 internal design suggest perhaps high sensitivity to specific noise frequencies ?

    Thanks,

    Yuval

  • 0 in reply to Yuval Yunger
    TI__Mastermind 40875 points

    We measure temperature error at min supply then temperature at max supply. 0.2C/V is calculated from that: (Tmax - Tmin) / (Vmax - Vmin)

    TMP275 continuously makes temperature measurements. These measurements take 27.5ms to 220ms depending on resolution configuration. I don't have any further information to share about the internal operation of TMP275. 

    thanks,

    ren