TI Multiplexers and Signal Switches often are designed without the need for an external logic supply, however, there are still many pin-to-pin multiplexer devices out there that still utilize this architecture that incorporates this supply pin. Thus, leading to the common question, what do you do if you want to replace your current multiplexer or signal switch that has a logic supply pin with one that does not?
When you have a true pin-to-pin device to replace that has this architecture, most of the time the logic supply pin will match up with a “no connect” (NC) or “no internal connection” (NIC) pin and can cause some confusion on how to handle such a situation. Let’s take a look at an example below between a device that has the VL pin integrated and the TI TMUX8212 which is a high voltage, 1:1 SPST, 4 channel signal switch in the 16-Pin TSSOP package:
As can be seen in the pinout above, everything is identical except for pin 12, which is the VL pin on the competition device and the NC pin on the TI TMUX8212 device. In this case, the existing design will be powering this pin with some low voltage supply that will now be seen at the NC pin of the TI multiplexer. When the pin is described as “no connect” or “no internal connection”, it is exactly as it is described. This pin is not bonded anywhere internally to the die itself and is just floating. So, applying a logic supply voltage on this pin will have no effect on the operation of the device and it will still be able to operate without issue as the logic supply is internal to the TMUX8212 device. In addition, this also means that floating this pin is perfectly acceptable as well as there is no internal function that this pin performs.
Lastly, without the need of that extra logic supply, this type of replacement will allow the designer to have access to an extra supply rail or control signal for their design where space and control options are always in demand. This would only be an option if there was an opportunity for a redesign as opposed to just being a drop-in replacement.
For more information on the NC/NIC pins and other potential unused pins on your multiplexer, please refer to our video on how to handle such situations below: