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?

  • \$\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

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.


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

  • 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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