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TMP300: Misbehaviour / abnormal performance

Daniel Smirr
Prodigy 80 points
Part Number: TMP300

Dear Team,

I am using the TMP 300 in a very simple design to detect an overvoltage:

It works very well and as expected, but sometimes I have an abnormal behaviour. The OUT pin sometimes toggles and the voltage at the VTEMP pin (measured with a dmm) is varying very fast, although the temperature of the part is changing very slowly. 

I already tried to change the TMP300, but nothing changed. 

Did you already see a behaviour like this with the TMP300?

Many thanks in advance

Kind regards

Daniel Smirr

  • 0
    TI__Guru* 91086 points

    Daniel -

    Welcome to E2E and thanks for posting !

    Couple questions back to start with. 

    1. are you using actually using electrolytic capacitors in your design? if so, you have them backwards in your schematic.

    2. Hysteresis pin should be connected to either GND or V+,not both. Have you tried removing R4 or R3?

  • 0 in reply to Josh Wyatt
    Prodigy 80 points

    Hello Josh,

    thank you for your reply.

    I am not using electrolytic capacitors, its just the way they are shown in the schematic editor.

    I removed the 100kOhm resistor from HYST to V+ (R4). 

    But it does not resolve my issue, it seems that the Vtemp pin is very very sensistive, does it make sense to increase the value of the capacitor (C1), for example to 1nF, or to add a series resistor between Vtemp pin and C1?

    Additionaly, I ve seen another phenomenon: when I cool down my pcb, approx. -30/-40°C (maybe a little bit lower), the nOUT-pin pulls down and the voltage at VTEMP rises above 2 V. Is this behaviour normal?

    Kind regards

    Daniel

  • 0 in reply to Daniel Smirr
    TI__Mastermind 35895 points

    Hi Daniel,

    Could you take a look with an oscilloscope? The VTEMP and TSET pins are both inputs to a comparator which drives OUT. If either of these signals is noisy, it can manifest in the OUT pin. Unfortunately, the VTEMP pin is not a very strong output driver as it has 210kohm output impedance. You may need to take steps to mitigate noise coupling into one or both of these pins by changing the routing or adding bypass capacitance.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 80 points

    Dear Ren,

    thank you for your message. I increased the bypass capacitance at the VTEMP and TSET pin (routing has already been very short).

    Now the behaviour is much better.

    Thank you very much

    Daniel