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TMP451-Q1: What is the twisted-wire pair connection in layout guide description?

Part Number: TMP451-Q1
Other Parts Discussed in Thread: TMP451,

Hi There, 

We plan to use TMP451 to monitor near-end MCU A and a remote Transistor to monitor far-end MCU B. I think it's topical application, so it shall have no risk, is it correct?

After reading the layout guide. I have one unclear point that may need your help to clarify:

" If the connection between the remote temperature sensor and the TMP451-Q1 device is less than 8-in (20,32
cm) long, use a twisted-wire pair connection. For lengths greater than 8 in, use a twisted, shielded pair with
the shield grounded as close to the TMP451-Q1 device as possible. Leave the remote sensor connection
end of the shield wire open to avoid ground loops and 60-Hz pickup."

What is the twisted-wire pair connection mentioned here?

Usually, the twisted wire pair only exited on "cable", in terms of PCB layout, it should only route as differential pair with proper impedance control.

Could you please have a further explanation for this point?

Furthermore, is there any Max length limitation between TMP451 and remote BJT?



  • Hi Frank,

    Please see the following FAQ for your question about the max length of the TMP451 and the remote BJT. Our expert Ren will comment soon on the twisted wire pair clarification.


  • Frank, 

    You're correct that twisted pair refers to cables. It is one strategy to limit induced noise, which remote sensors are sensitive to. We recommend using copper pour in PCB to create shielding for the same reason. 

    There is not a max length, but a practical limit to length is imposed by series resistance and parasitic capacitance of the traces or wires. Note that while we automatically correct for errors due to resistance, the effective RC (normally dominated by capacitance) causes the error shown in Figure 6.