[sdiy] Outputs grounded! Re: SSI2164 datasheet updated

Tom Bugs admin at bugbrand.co.uk
Sat Aug 11 21:17:06 CEST 2018

I was also surprised by the outputs ground requirement in the app note.

I seem to remember the question about what to do with unused 2164 
sections coming up on the list some years back.
I'd previously tied inputs simply to 0V, but someone (I think it might 
have been you, Neil) suggested that would be bad and that the standard 
compensation network should be used and a 30k to 0V.
Since then I've tended to add the regular compensation network - partly 
as it typically makes layouts symmetrical around the 2164 & costs almost 

On 11/08/2018 19:30, Neil Johnson wrote:
> The 2164 has current inputs and current outputs.  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.  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.
> The inputs are really current summing nodes, so connecting them to GND
> is also equally valid.
> And it was not "suddenly" - the 2164 has always been like this.
> Neil
> On Sat, 11 Aug 2018 at 19:07, KD KD <pic24hj at gmail.com> wrote:
>> Most folks dont ground OPAMP, logic's, LM13700 outputs so why suddenly 2164's?
>> Do you ground OPAMP outputs and take the chance of sudden system current
>> increase despite manufacturers suggestion to leave unused outputs open?
>> 2018-08-11 19:48 GMT+02:00, Michael Zacherl <sdiy-mz01 at blauwurf.info>:
>>>> On 11 Aug 2018, at 19:08, KD KD <pic24hj at gmail.com> wrote:
>>>> outputs should grounded;
>>> excuse my ignorance, but really? I.e. no input == no output current?
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