Help needed with IC substitution problems......

[TERRA Operative]

I'm currently building a DC Bias Option board for my HP 4276A LCZ meter and I am having a little trouble with substituting the old, obsolete and expensive LF13331D Analogue Switch with an in production (and substantially cheaper) TC4066BP Analogue Switch.

I'm sure there's something basic that I am missing here, but I've come to a blank trying to get this to work.
When I made this circuit with the LF13331, it worked perfectly but with the same circuit adjusted to use the TC4066BP, it's just not working..
Basically, every time I plug the TC4066BP on, it pulls the 6.3V rail right down, even if I leave the control pins disconnected.

I've included the original and new schematics below, along with datasheets of both parts. If someone smarter than me can take a look and tell me what I'm doing wrong, that would be greatly appreciated.


The first attachment is my revised schematic, the second is the original HP schematic.

[Jay_Diddy_B]

Hi,
I can tell you what is wrong. It may take a little while to come up with a solution.

The original part LF13331 was powered from +/-12V

The TC4066 is powered from +12V and ground.

The TC4066 is limited to 20V max operation.

The switch pins have to be inside the rails for the switch to work.

In your design you are shorting the 6V3 rail to ground through substrate diodes in the TC4066.

Regards,

Jay_Diddy_B

[oPossum]

DG412 may work as a substitute for the LF13331.

https://www.vishay.com/docs/70050/dg411.pdf

[Jay_Diddy_B]

Hi,
I was going to suggest ADG444. Similar to oPossum's suggestion.

Power with +/-12V and 5V on Vlogic

Jay_Diddy_B

[TERRA Operative]

Aaahh, I knew the devil was in the details somewhere....

Thanks for the info, I'll take a look at those suggested substitutions and see what ones I can get easily here.

[German_EE]

Why not power the 4066 with +/- 6.3V from either side of the zero adjust control?

[Jay_Diddy_B]

Why not power the 4066 with +/- 6.3V from either side of the zero adjust control?

Good idea, but...

The control pins are driven by 0-5V logic signals

The thresholds on the TC4066B are with respect to VSS. You would have VSS at -6.3V.

You would have to level shift the control inputs.

Other switches like the ADG and DG family have the level shifter built in.

Jay_Diddy_B