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TMP431: can we estimate temp. accuracy using FPGA internal BJT

Alan Chang
Intellectual 2160 points
Part Number: TMP431

Hi, 

   if TMP431 connect FPGA internal BJT as remote sense, but the BJT spec. is higher than TI recommendation on data sheet, item 3 and 4. 

1. Base-emitter voltage > 0.25 V at 6 μA, at the highest sensed temperature: OK

2. Base-emitter voltage < 0.95 V at 120 μA, at the lowest sensed temperature: OK

3. Base resistance < 100 Ω --> FPGA resistance is 210 ~ 287 ohm

4. Tight control of VBE characteristics indicated by small variations in hFE (that is, 50 to 150): hfe is 200~ 250.

      On this case, can we estimate temperature accuracy or tolerance? How can we calculate?  

  • 0
    TI__Mastermind 28070 points

    Hi Alan,

    The TMP431 should be able to cancel up to 1kOhm of series resistance when beta compensations is not enabled, and up to 300Ohm when beta compensation is enabled. If this transistor needed beta compensation I would say that the base resistance was cutting it very close, and they could possibly have issues due to parasitic resistance. Figure 8 from the datasheet provides some guidance on how much series resistance can affect the accuracy when beta is low.

    However, this BJT sounds like it will be fine, given that the HFE (Beta) is so high, and they should not need beta compensation. As long as they do not exceed the 1kOhm series resistance limit, and their N-factor can be accounted for, they should not see additional error. 

    Best Regards,
    Brandon Fisher