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LM321: Plug in replacement for LM321 SOT23-5

Jim Labrecque
Prodigy 195 points
Part Number: LM321
Other Parts Discussed in Thread: TLV9301, TL343, OPA990, LM7705

Does TI offer a drop in pin for pin replacement for the LM321?  I looked at the TLV9301 which is the suggested replacement, but unless I am reading it wrong,  the pin out for the SOT23-5 is different than the LM321.  I need a device that can handle a +15V rail. 

Thanks, Jim

  • 0
    TI__Mastermind 33011 points

    Hey Jim,

    There is one other pin to pin device that can support a 15V rail, and that is the TL343. Could I ask why you are looking for a drop in for the LM321? Is it a performance limitation or supply?

    Best,
    Jerry

  • 0 in reply to Gerasimos Madalvanos
    Prodigy 195 points

    Performance-  We are using it in a single supply application and the devices sinking capabilities as the output signal gets close to ground really degrades.  In looking at the TL343, I don't see any output current ratings.  I wonder since it is bipolar whether its output structure has similar issues to the LM321.

  • 0 in reply to Jim Labrecque
    TI__Mastermind 33011 points

    Hey Jim

    The output close to negative rail gets better with a true rail to rail output device, like the OPA990. The LM321 had to have a unique architecture . Unfortunately we don't have a pin-to-pin option with rail to rail output. The TL343's swing from rail is not stellar (this spec is given with +/- 15V supplies):

    There's another way to eke out a little low voltage performance, but it also requires a re-spin of the board. https://www.ti.com/product/LM7705

    LM7705 will make a small negative voltage rail so your op amp output can swing all the way to 0V. However, if you are adding that part in, you may as well just skip a step and go to the OPA990 or the TLV9301 where you can swing 50mV from rail with light load and with no load 5mV from rail.

    There are rail to rail output bipolar devices, but these can only swing a couple hundred mV from rail. CMOS can get closer to rail, but will degrade faster under load conditions.

    Best,
    Jerry