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TMP20 Questions

uMin
Intellectual 860 points
Other Parts Discussed in Thread: TMP20

Hi,

My customer has an application that requires a very low current consumption temperature switch/sensor, ideally 1uA or less,as it is powered from a coin cell battery. And it has to trigger when the temperature is above 100C.  We are considering TMP20.

 

To save power, we intend to pulse the Vcc of the temperature sensor such that it is 1msec on / 10msec off.

 

Questions:

 

  1. The datasheet has a graph (Fig2) Iq vs Temp at Vcc=5.5V, and another graph (Fig4) on Iq vs Vcc at Temp=25C.  We need to know the Iq vs Temp (25C to 150C) at Vcc=2.5V. Can we assume it is similar to !q vs Temp at Vcc=5.5V ?  Since the Iq is relatively constant from 2.5V to 5.5V at 25C.
  2. What is the response time of TMP20 ?  ie. When it is powered from 0 to 2.5V, how long will the output be valid ?
  3. In Fig 10 Thermal Settling, it indicates TMP20 takes about 6 sec to response to a temperature step from 25C to 110C.  If Vcc is pulsed with 1msec on / 10msec off, what will be the thermal step response like ?
  4. We inted to add a MOSFET to the TMP20 output to make it works like a Temp switch such that the output is active low when it is above 100C.  Any recommendation on the MOSFET or circuit ?
  5. Another "brute force" method is to use a pull up resistor ~1Mohm at the TMP20 output to make it look like an active low output.  Will it cause any harm to TMP20 ?

 

Or, is there other better solution to fulfill the low power (~1uA) temperature switch requirement, which will trigger when >100C ?  Accurarcy is not so important, but low power is the key factor.

 

Thanks,

 

CM.

 

  • 0
    TI__Expert 6930 points

    Hi ZD,

    Thank you for your question regarding TMP20 and low power consumption.  I will look into any existing data regarding duty cycle modulating the power supply and come back to you in this forum thread.

  • 0
    TI__Genius 14825 points

    CM,

    1. We do not have the data you have requested, all we can confirm is the Iq at 2.5V at room temperature matches the Iq at 5.5V at room temperature from figure 4, as you pointed out.  Also, if you want to run the device to +150C, please understand that this is the up to the absolute maximum limit and the operating range of the device is only up to +130C.  We cannot guarantee operation of the part within spec if you exceed the operating range of the device.

    2. We don’t have data on this but I hooked up a TMP20 and pulsed the power on and off a few times to see what a typical response time (power on to settled output voltage) is, and it appears to be just under 1ms.  Given that this is just one device and a few sample runs, I expect some devices may take longer than 1ms to reach a settled output voltage.

    3.     We don’t have data on this mode of operation and those conditions.  I'm not sure if this applies to your use case though, this is essentially the response for a constant powered device with a large and abrupt temperature change.  Without knowing more about your use case, I cannot say what the response time is but this should be a worst case situation for temperature measurement.

    4.     Figure 12 of the data sheet shows a suggested circuit for setting up the TMP20 as a limit switch but it doesn’t use a MOSFET.  I don’t have a MOSFET circuit beyond that to recommend.

    5.     I can’t recommend driving current into the analog output of this device, however if you keep the Iload between -600uA and 600uA per the data sheet spec, you will see a typical change of 6mV or so.


    Thank you for your interest in the TMP20, I’m glad to help as best I can if you have further questions.

    Jason Bridgmon

  • 0 in reply to Jason Bridgmon
    Intellectual 860 points

    Hi Jason,

     

    Thanks for your meausrement and reply.  Apprieciate your help.

    My customer will implement a 1Mohm pull up at the output pin to a button cell (2V to 3.6V max) on their circuit.  This will mean a max 3.5uA current of iload into the output pin.  At most of the time at room temperature, the iload should be much lower.

    Just want to confirm that this will not cause damage to the device, since iload is way below the spec of ±600uA.

     

    Thanks,

    CM.

     

  • 0 in reply to uMin
    TI__Genius 14825 points

    CM,

    That was about the current I calculated from your notes, I think it will be okay.

    Thanks again for looking into TI Products!

    Jason