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TMP422: Compared with TMP421

ArTzy
Genius 17525 points
Part Number: TMP422
Other Parts Discussed in Thread: TMP421, TMP441, DXP

Hi Experts,

Good day!

A client is requesting TMP421 orderable device and turns out to be out of stock as of this writing. We've found TMP422 device. Can this temperature sensor device would work same to the former (given with the same pinouts/packaging; thus, no SW/HW changes?

I could see that they have different numbers of remote channels and address.

Thanks for your guidance.

Regards,
Archie A.

  • 0
    TI__Mastermind 43805 points

    Hi Archie,

    No, TMP422 is not a drop-in replacement for TMP421. The A1 and A0 pins on TMP421 become DX3 and DX4 on TMP422. The datasheet states either DX3 or DX4 must be tied to GND while the other floats for reliable address detection on TMP422. If by some miracle the customer had left one A# at GND and the other floating (one of several options, and not the first I would pick,) the TMP422 would still not be software compatible because it would choose a different I2C address than what TMP421 would choose in the same PCB. 

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    TI__Genius 17525 points

    Hi Ren,

    Thanks for your response. How about the TMP441? Would it be a drop-in replacement for TMP421? If not, may I know also the reason?

    They have the same number of remote channels and addresses. Thus expecting it to be a good drop-in.

    Thank you

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 43805 points

    Archie,

    TMP441 is a suitable replacement, but it would not be 100% software compatible due to the Device ID.

    • The Device ID register 0xFF reads 0x21 on TMP421 and 0x41 on TMP441.
    • TMP421 does not have Beta Compensation feature or Beta Compensation register at address 0x0C. The TMP441 will power-on in the Auto Beta Compensation mode, which may select a low beta range and N-Factor of 1.000 if the connected junction is a 3 terminal PNP (DXP:Emitter, DXN:Base and collector current returned to GND via 3 separate paths.) If this happens, the reported temperature will be different than what TMP421 would report due to change in N. The intention is for Beta Compensation to automatically enhance accuracy; I’m just pointing out that customer could observe a different result than they’re used to.
    • If they are using N-Correction register 0x21, the behavior of this register may be changed slightly by Beta Compensation as noted above. When Auto Beta Compensation detects a PNP transistor, it will use N = 1.000. If it detects anything else, it will use N=1.008 the same as TMP421. The encoding/scaling of the N-Correction registers moves with this 1.000/1.008 change.

    thanks,

    ren