[sdiy] [OT] LM13700 spotted in commercial product of big Manufacturer

mskala at northcoastsynthesis.com mskala at northcoastsynthesis.com
Sun May 15 13:04:23 CEST 2022

On Sun, 15 May 2022, Roman Sowa wrote:
> Why would ever LM13700 disappear?
> It's the cheapest OTA with thousands of uses.

There are two different issues being conflated in this thread.

The LM13700N, meaning the DIP version, certainly can be discontinued
because it already has been.  Texas Instruments PDN number 20210505000.3
announcing this was dated a year ago Thursday - May 12, 2021, with the
last order date being one year later.  I have my "last time buy" box right
here, next to my similar boxes of TO-92 transistors.  "Why" they would do
this is no longer a high-priority question given that it did happen, but
the PDN says "Reason for Widthdrawal/Discontinuance:  The die attach for
these products is being discontinued."

That is probably what the original poster had in mind when describing the
use of an LM13700 in a new design as "unwise."  However, it was just
specifically the DIP version that was discontinued by TI, and I think it's
unlikely that Fender is actually using the DIP version.

All DIPs in general are on borrowed time, a fact which concerns me given
that I really like DIPs and I sell products that use them.  I've talked
about it several times in my video stream (Mondays, 3pm Eastern,
"matthewskala" on Twitch).  There are DIP LM13700 clones available from a
couple of Chinese manufacturers.  CoolAudio offers a 13700, and their data
sheet mentions a DIP version, but it's not clear that they really make and
sell anything but the surface mount version.

The LM13700 - no suffix, meaning the silicon die that might be packaged
some other way than DIP - is a different question.  That is a popular IC
with a big market, and it would be harder for TI to discontinue all
versions of it than to discontinue just the DIP version.

But they still could!  Remember that one important reason the LM13700 is
so popular now is because it is pretty much the last OTA available.  Many
people using the LM13700 would really prefer to use the CA3080, CA3280, a
Roland custom chip, or similar... but those are all gone.  Being the last
one available improves its marketability, but the reasons why the others
were discontinued do also apply to the LM13700.

The only remaining TI LM13700 is the LM13700M, the -M as opposed to -N
denoting the SOIC16 package; and SOIC is a "dated" package too.  It's
surface-mount and seen as more modern than DIP, but it's basically the
oldest generation of surface-mount.  Most mass-produced designs are aiming
for smaller packages and the fact the LM13700 is not offered in a smaller
package does not bode well for it.  If they really thought this was a chip
with a strong market for the long term, they would be introducing newer
packages for it.

Consider the CA-series chips, like the CA3080 and CA3280.  All of the
CA-series chips are gone now because they had to be made on a special
process that offered physically large bipolar transistors for analog
circuitry - totally different equipment from what's used for making modern
digital CMOS.  Eventually the company that ended up owning that production
line after however many mergers (I don't even remember who it was), didn't
see the business case for running the special CA-series semiconductor
process anymore.  Quite possibly, there was only one technician who knew
how to run those machines, and that person retired.  All analog bipolar
processes will go that way some day; and new ones are not being created to
replace them.  New analog processes, to the extent they exist at all, are
CMOS processes.

So I don't think the LM13700 is secure forever, even though it's probably
secure enough for the next few years that Fender can reasonably use it in
a new design; provided they're not using the DIP version, which is
already discontinued.

> Just like TL0x, LM324, NE5532, LM2902 and other ancient designs it's not going
> anywhere simply because it's cheap, and for decades used by large companies in

TL07x is an interesting case.  Go to the TI Web page for the TL074 and
there's a big notice on it saying "A newer version of this product is
available," pointing at the TL074H.  Read the data sheet for the TL07x
chips and it is conspicuously two data sheets.  Nearly all the tables of
actual data are split into "TL07xH" and "all others."  The top bullet
points on the front page, and the first paragraphs of the main text
sections of the data sheet (sections 3 and 8) are devoted to telling
readers that the TL07xH is better than the other versions.

Notwithstanding the similar model number, it seems clear that the TL07xH
is a completely different product, with a much newer design, and TI is
strongly encouraging you to use it instead of the traditional TL07x.

The TL07x "all others" chips are JFET-input bipolar chips.  They would
have to be made on a process specifically designed for such, and not
useful for much else.  The TL07xH is analog CMOS, presumably made on a
different process much more similar to processes used for modern digital
CMOS.  It doesn't mention CMOS in the data sheet, but does on the TI Web
site.  References to JFETs have been removed from the TL07x data sheet
text, although the schematic in the data sheet still shows JFETs and BJTs
and there is no schematic showing MOSFETs.  The TL07xH is also surface
mount only.

We don't need a weatherman to tell which way this wind is blowing.

Matthew Skala
North Coast Synthesis Ltd.

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