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A search for voltage reference LM385B reveals that most of its many versions come in either 3-pin TO packages or 8-pin SOIC/TSSOP packages. Very few are 3-pin SOT-23 packages. I was wondering why is this? Why have 8 pin packages where 6 pins are NC?

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  • \$\begingroup\$ Some devices have a larger die size. \$\endgroup\$ – Ignacio Vazquez-Abrams Sep 21 '16 at 0:51
  • \$\begingroup\$ If the silicon die size is too large to fit insize the die cavity of a SOT23 package, then the larger 8SOIC package would be needed. \$\endgroup\$ – MarkU Sep 21 '16 at 0:51
  • \$\begingroup\$ Hmm I haven't come accross 2 pin regulators yet. Are they just fancy zener diodes? I wonder why a normal zener wouldn't suit the job. \$\endgroup\$ – Bradman175 Sep 21 '16 at 8:49
  • \$\begingroup\$ @Bradman175 -- they're used the same way as Zeners, yes, but provide better performance than a Zener (i.e. more accurate and stable over temperature and time) \$\endgroup\$ – ThreePhaseEel Sep 21 '16 at 11:33
  • \$\begingroup\$ @ThreePhaseEel Seems as I expected. \$\endgroup\$ – Bradman175 Sep 21 '16 at 11:36
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There are multiple issues at play here, actually. Die size, as mentioned, is one of them -- a SO-8 or even a TSSOP-8 can accommodate a larger die than a SOT-23 can, although modern references are available in SOT-23 packages these days (the Intersil FGA parts come to mind, specifically).

Other reasons include mechanical stability for high-accuracy references and the need to provide post-packaging trim access due to packaging process induced shifts in the reference voltage. LTC AN82 discusses these problems in more detail.

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Std Packages are selected for automation, so another tool adapter does not have to be purchased.

8-DIP, TO-92, SOIC and TSSOP are avail

The TO-92 has 3 leads like small signal transistors

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  • 1
    \$\begingroup\$ What makes SOT-23 not a standard package, in this context? \$\endgroup\$ – The Photon Sep 21 '16 at 1:28

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