Unused CMOS inputs

[Harry Bissell]

Hi Chris (and list)

You may ground CMOS inputs, or tie them to V+ (the highest voltage that the
chip uses) or in rare instances to V-, but not if V- isn't the lowest voltage
on the chip...

Example CMOS running on +12 and 0V, tie unused inputs to either...
                CMOS running on +7.5 and -7.5, tie unused inputs to either...
NOT to 0V
                CMOS running on +12 and 0V, DO NOT TIE ANY INPUT to a
voltage outide this range...

There are some CMOS chips which have special abilities with respect to
voltage (some can translate voltages up or down)...consult the data sheet.

You can also tie a CMOS input to another input or output... it goes along for
the "ride" but adds 5-15pF extra capacitive load... usually OK but not in
some sensitive circuits...

The LM13600-13700 buffers aren't CMOS. (assuming a bipolar supply) I'd tie
the buffer input to V- for the LM13600 and float the output, and tie the
LM13700 input to ground or V- and float the output.  Somebody stop me if this
is bad advice on this chip....

:^) Harry

PS. Chris... heard a rumor you have a CD??? Care to swap ???  :-) Harry


macdonald at evenfall.com wrote:

> I have read that it is good practice to ground unused CMOS inputs to
> prevent unintended behaviors.  Is it also acceptable to set them to V+ or
> V-?  This would be really convenient when not using the buffers in the
> LM13700 for instance.
>
> Thanks,
>
> -Chris MacDonald