LMT87: Converting 3-wire into 2-wire for 3m long cable transmission over twisted pair

Neet

Part Number: LMT87

Tool/software:

Hello E2E Community,

We are currently exploring LMT87 for our temperature measurement use case, where we have to measure the temperature of the bearing which is about 2-3m away from the MCU board.

We are planning to use a high gain TO-92 package sensor - LMT87 from TI's analog sensor portfolio for this use case.

Kindly guide us if we can convert the 3-wire interface of this sensor into a 2-wire configuration by connecting the voltage output at the sensor side to the Vcc via a suitable resistor?

Also can you guide us on the RC filter that we plan to install on the ADC side? Our current plan is to use a RC based LPF with R: 10kOhm & C: 0.1uF.

Reference Design for 3-Wire to 2-Wire configuration

Kindly guide.

1 month ago

0 Alex Thompson 1 month ago

TI__Expert 5670 points

Neet,

Could you please clarify why it is necessary to tie the output to the Vdd through a resistor? This is not a good idea, I don't know how you would read the output. The only way to use this device is to use it as intended and described in the datasheet, without any of its pins tied together.

Regards

-Alex Thompson

0 Neet 1 month ago in reply to Alex Thompson

Intellectual 532 points

Hello Alex Thompson,

2-wire is a more common (& often efficient) configuration for sensor data transmission over few meter long cables instead of 3-wires.

Now TI engineers have recommended ways to achieve 2-wire configurations from 3-wire Hall Effect sensors, hence I am inquiring if this is possible to execute with LMT8x series - in essence we are converting the voltage output signal into current output which is then sensed at the controller side using a sense resistor. Kindly loop in someone who is aware of this configuration if you have not come across such use cases, it might help both of us equally.

0 Alex Thompson 1 month ago in reply to Neet

TI__Expert 5670 points

Neet,

This is not a valid use case of LMT87. If you want a 2-wire temp sensor where the current varies with temp, you can look at LMT01, which has a IQ pulse count interface, or try TMP61.

Regards

-Alex Thompson

0 Neet 1 month ago in reply to Alex Thompson

Intellectual 532 points

Okay,

Yes, we are considering these all simultaneously right now before we order EVMs & before we select the final sensor for our use case.

Thank you for the clarification on this configuration, I appreciate it.

0 Alex Thompson 1 month ago in reply to Neet

TI__Expert 5670 points

Neet,

No problem, happy to help.

Thank you

-Alex Thompson

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LMT87: Converting 3-wire into 2-wire for 3m long cable transmission over twisted pair