• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 333 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMP61-Q1: Criteria of the resistance tolerance

Akihiro Hirata
Expert 6200 points
Part Number: TMP61-Q1
Other Parts Discussed in Thread: TMP61

Hello team,

1. Criteria of the resistance

D/S says resistance tolerance is +/-1% and 1.5% based on the temp range.

Note (1) says "Limits defined based on 4th order equation, tolerance will change with 'Sensor Long Term Drift' specification."

So criteria is based on below equation in the thermistor design tool?

If so, the below 4th order polynomial is guaranteed equation, right?

2. If my understanding of the above question is correct... 

Below Datasheet table says minimum is 9.9kOhm and max is 10.1kOhm at 25C.

On the other hand, the resistance derived from 4th polynomial equation, it is 9959 Ohm based on the thermistor design tool.

When we look at the below table, It means 9859 Ohm is minimum and 10058 is max according to below table

.

If the resistance of 25C is 10.1kOhm, This meets R25 spec but this doesn't meet RTOL TA=25C spec.

How to think about this?

Should we think minimum is 9900Ohm and maximum is 10058Ohm to meet both spec?

3. Calibration.

Your team suggests the 1 point (room temp) calibration to enhance accuracy. 

How to achieve this? Is this calibration method covered in the thermistor design tool?

Thank you.

Regards,

Hirata

  • 0
    TI__Genius 9675 points

    Hi Hirata-san,

    The first thing to mention about the TMP61 is that it is a silicon-based thermistor. The distinction between the TMP61 and an NTC is that the TMP61 is a current mode device. The current through the device, as well as the temperature, changes the effective resistance. What this means is that depending on the bias resistor and voltage bias you have in your thermistor circuit, the nominal resistance will change slightly. The nominal resistance will also change slightly depending on the package chosen. With the understanding of this device, we can look again at your questions.

    The tolerance specified in the datasheet is for a certain configuration of 200µA bias and 3.3 Supply voltage. If you change this configuration, you will most have to adjust the nominal resistance as such. The thermistor design tool allows for the flexibility of changing the design parameters and will generate the 4th order polynomial equation for you. It is a guaranteed equation, and although it may vary slightly from the 10k @ 25°C that is shown in the datasheet, it will still meet the 1% and 1.5% tolerance. Please take a look at the thermistor design tool and use the provided 4th order polynomial from there.

    We do have information regarding the calibration with the TMP61. I can provide a presentation that covers this for you offline if that would be helpful.

    Jalen