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TMP468: choosing the BJT sensors

John Chou62
Intellectual 2080 points
Part Number: TMP468


Tool/software:

hi Team,

customer studying TMP468 and according to the BJT request in the datasheet (P.32)

TI recommends using MMBT3904 (NPN) or MMBT3906 (PNP) and needs to meet the following:

they are consulting with their BJT vendors but have some questions 

  1. Does the current of “7.5uA” and “120uA” refer to IB, IC or IE?
  1. Does “Base resistance” refer to “rπ” in small-signal equivalent model (like follow figure)?

  1. “Tight control of VBE characteristics indicated by small variations in hFE (50 to 150).”

Could you have a more specific explanation?

For example, the specific scope of “Tight Control”, etc

thanks for the assistance

  • 0
    TI__Mastermind 44085 points

    See Figure 23 from the TMP468 datasheet.

    Current is sourced from D+ pin. 

    Ie and Ic are expected to be about the same in all configurations while Ib will depend on transistor properties.

    A good transistor will have low device-to-device variation in this low-current operating region. That is what is meant by "tight control" and "small variation."

    thanks,

    ren