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TMP61-Q1: what does Vsns mean?

Elec Cheng
Expert 7055 points
Part Number: TMP61-Q1
Other Parts Discussed in Thread: TMP61

Hi Expert,

Our customer uses TMP61with current bias. They find some confusion in datasheet. As you can see below, the Vsns is recommended to work at 5.5V max. From my understanding, Vsns means the voltage between Thermistor (–) and (+) terminals. But also in datasheet, we see the test curve, when Ibias is 400uA and at 140C, res is about 20k, so the total voltage on TMP61 will be about 8V, which exceeds 5.5V as recommended. So I want to know if I understand correctly since it's very weird. Please help clarify. Thanks.

BR,

Elec Cheng

  • 0
    TI__Genius 9675 points

    Hi Elec,

    The TMP61 is intended to be used with a current source. It is a current-mode device. The resistance table is an "effective resistance" to help as customers are used to working with NTC thermistors.

    The key parameter when using a current source implementation will be ISNS  . The max recommended spec for this is 400 µA. As long as this spec is met the device will operate as expected.

    Thanks,

    Jalen

  • 0 in reply to Jalen Tate89
    TI__Expert 7055 points

    Hi Jalen,

    Jalen Tate89 said:
    The key parameter when using a current source implementation will be ISNS  . The max recommended spec for this is 400 µA. As long as this spec is met the device will operate as expected.

    So do you mean, under current bias mode, the voltage between TMP61 can exceed 5.5V? From my understanding, the recommenced table limit all the parameter the device  need to follow while working. Am I wrong? Thanks.

    BR,

    Elec Cheng

  • 0 in reply to Elec Cheng
    TI__Genius 9675 points

    Elec,

    I will need to correct myself here. Both recommended operating requirements will need to be met in order for the TMP61 to operate without damage. The voltage between TMP61 can not exceed 5.5V. 

    This means, if your customer is using a 400 µA current source the operating temperature range will be limited from -40°C to ~80°C. If a larger operating temperature range is needed, I recommend using a 200 or 300µA current source instead.

    Sorry for the confusion,

    Jalen

  • 0 in reply to Jalen Tate89
    TI__Expert 7055 points

    Hi Jalen,

    But the figure9-7 shown in datasheet covers 150C with 400uA. Is it not so correct? Seems this part will cause some confusion. May you help double confirm? Thanks.

    BR,

    Elec Cheng

  • 0 in reply to Elec Cheng
    TI__Genius 9675 points

    Elec,

    I agree that it may cause some confusion. We will work to correct this, so thank you for bringing it to our attention.

    There should be a limit to the temperature covered, limited by the 5.5 operating max voltage, indicated on the chart somewhat similar to the yellow dash line I have added.

    Jalen