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AMC6821: NPN transistor connection

Sunset
Genius 13985 points
Part Number: AMC6821

Hello Team,

The AMC6821 shows the PNP transistor in the schematic (Figure 13) but we recommend NPN.  As discussed in other topic we have qualified NPN so we really recommend NPN, while it would work for PNP transistors as well.

Making the PN junction out of the transistor look strange in the datasheet.

I would have assumed a connection like in the current mirror, with a collector tight with the base.

But this is not the case.

How shell I connect the NPN transistor to the AMC6821.

  • Shell the collector be connected to the base? (as below)
  • If not, why and how?

Thanks,

SunSet

  • 0
    TI__Mastermind 28075 points

    Hi Sunset,

    You are correct. You will want the connect the NPN in a diode connected configuration like you have shown.

    This allows the AMC6821 to properly set the current value of the diode during measurement.

    Best Regards,
    Brandon Fisher

  • 0 in reply to Brandon Fisher94
    TI__Genius 13985 points

    Hello Brandon,

    thanks for the confirmation.

    I would like to ask an update on the datasheet.

    • The configuration shown in the schematic is different, does not have collector connected with the base.
    • We recommend NPN and the schematic shows a PNP.
    • Since at the end is a diode what matter, we may add both use cases.

    These brought already questions.

    Thanks,

    SunSet.

  • 0 in reply to Sunset
    TI__Mastermind 28075 points

    Hi Sunset,

    I will pass your request onto the rest of our team. Please understand that we are unlikely to update this datasheet due to the age and the fact that the information in it is correct. We prefer to leave datasheets for older parts alone (unless any bad information is present) to avoid causing any confusion at customers that have already been using the part for years. 

    I should also note that the AMC6821 was actually optimized to work with the internal diodes available in Pentium M and IV Processors. The datasheet suggests a "general-purpose 2N3904 type transistor" (The PNP version of the 2N3904 is the 2N3906) just as an external alternative. 

    Best Regards,
    Brandon Fisher