[sdiy] Outputs grounded! Re: SSI2164 datasheet updated

[KD KD]

2018-08-11 20:30 GMT+02:00, Neil Johnson <neil.johnson71 at gmail.com>:

> The 2164 has current inputs and current outputs.
Yes i know that and the current out is rater small.

> In fact you are *required* to force the output to the same(ish) voltage as
> the GND pin this usually done with the virtual earth node of an inverting
> op-amp, but there is no reason for connecting it directly to GND.
Okelidokkeli , i dont really understand ,so if no reason to directly connect
unused output to GND why is it a requirement then? If output loaded with
say 1Mohm to GND would that make that section go berserk?

> See  the datasheet where it talks about "Output Compliance" - that is
> how  far the outputs are allowed to stray from GND before bad things
> happen.
Yes its low but how bad, latch-up? Or severely affecting other sections used?

> And it was not "suddenly" - the 2164 has always been like this.
What i meant by suddenly is that i cant recall it was mentioned in the
original AD datasheet. So when in time was there a debate "somewhere"
about this? Just as i missed the original diode protection thing at its time.

2018-08-11 20:41 GMT+02:00, mskala at ansuz.sooke.bc.ca <mskala at ansuz.sooke.bc.ca>:
> Op amps have voltage outputs, intended to feed into relatively high
> impedance.
Some opamps are designed to feed relatively low impedances as well.

>The 2164 has current outputs, intended to feed into virtual
> grounds with relatively low impedance.
Relatively low such as?

> If you leave an unused 2164 output  open, it''ll be trying to force current
> into a place where no current can  go, which probably won't exactly harm
> anything but will mean some of the transistors are not at their intended
>operating points, and it could affect the performance of the parts of the
> chip you are using.
 OK so this is the "real catch" of the 2164, other sections can be affected?
Im not user of 2164 more then textbook VCA /VCF so i haven't studied
the 2164 in full.

> The LM13700's OTA outputs are current outputs too and should ideally go
> into virtual grounds for best performance, although not all popular
> LM13700 circuits do that.  Its buffer outputs are voltage outputs and
> should be left open if not used.
LM13700 im talking about the OTA output not the bufferoutput.
So the 2164 actually have worser compliance then a LM13700?

Ok ,so now DIXON says they left thousands outputs unconnected with no problem!
I have to take him for his words really.