LM13700N Unused Pins?

[Arn C.]

Howdy Folks!

     I am working on a project that uses a LM13700N.   I am only using half of the IC.   Do I ground the input or output of the other amp and the other buffer? 


Thanks!
Arn C.

[gez]

I'm sure this question has come up at least once before, but I can't remember the answer.  So long as there's no current going to the Iabc pin of the unused half, then there's probably no need to do anything...but don't quote me on that! 

If you're unsure, give it a trickle of current and wire the inputs to your bias reference (possibly wire one input via a largish resistor).  Can't hurt (famous last words!)  No need to hook up the buffer and definitely don't ground the output.

The reason I'm not 100% sure is because I've never left half of a 13700 unused.  Why would you want to?!  See this as an opportunity to do something a little extra with your circuit (it's a damn versatile chip).  What's the circuit?

[frequencycentral]

It will be fine to leave the unused side unconnected - though you could consider using the very useful darlington pair as a buffer elsewhere in your circuit.

[Arn C.]

Thanks Gents!   I am making a sort of sustain circuit,  but I really don't know what else I could do with the other half of the IC.   Maybe make two of the same circuits and mix them?  Or make some other circuit -"OD" and mix that in?   I am unsure,  but I will look at some other circuits that use this chip, maybe that will give me some ideas.

I just remembered that it was the unused pins on the cmos chips that you can ground(not sure if it was inputs or outputs)


Peace!
Arn C.

[frequencycentral]

The 'other half' could be: a Ring Modulator, a VCA, a VCO, a 6db/oct VCF etc. Do a google search for the spec sheet, interesting reading.

[Arn C.]

Thanks Rick for the info !

Arn C.

[gez]

The 'other half' could be: a Ring Modulator, a VCA, a VCO, a 6db/oct VCF etc. Do a google search for the spec sheet, interesting reading.

Using the other half for a VCO perhaps isn't such a good idea as the supply pins are shared, so there's a strong possibility of bleed-through from the oscillator into the audio chain.  In the past I've used one half of the LM13700 to shape an LFO's square output into a trapezoid and then used the other half for audio, but I was meticulous with ground paths etc.  It worked, but it was chancy.

As you say, though, the data sheet has plenty of applications.