max. current through a 4066 switch

--- The data sheet for the CD4066 at:

indicates that the maximum allowable current into any input is 10mA, so you're OK there but, since the switch resistance can go as high as 240 ohms with a 15V supply (480 ohms witha 10V supply), you won't meet your 1V drop spec, since:

E = IR = 0.01A * 240R = 2.4V

The data sheet for the HC4066 at:

indicates that the absolute maximum supply voltage is 7V, so you're screwed there, too.

If you don't want to use a mechanical relay why don't you try something like:

-- John Fields Professional Circuit Designer

He can use 74HC-series analog switches, if he switches to the 74hc4053 and its friends. These can be powered from +/-7V, and have 28-ohms typ, 80-ohms max at +/-6V according to ON Semi, and 45-ohms typ, 80-ohms max at +/-6V according to ST and Toshiba.

Yep, Make sure you buy the ON-Semi ones, redesigned for manufacture on Chartered's process by yours truly ;-)

...Jim Thompson

How much charge injection ?:-)

...Jim Thompson

Or GaAs fets, if you don't mind a lot of leakage and jfet-like behavior.

John

I still have the files. What would you like to know?

...Jim Thompson

I cannot find the maximum switch current in any data sheet of the 4000 or HC4000 CMOS analogue switches. I'm afraid I'll take the n or p MOSFET out of its ohmic region. I need to switch 10mA , and can afford up to about 1V drop. Can it be done with a 4066 (typ. Ron=80 ohm @ Vdd-Vee=12V) ?

If not how about the 74HC4066 (typ Ron=30 ohm @ Vdd-Vee=12V) ? I want to avoid a relays if possible.

Adam

In article , Adam S wrote: [....]

There's about a million miles between a CD4066 and a relay. Before you make that long of a jump consider using a discrete JFET or MOSFET or a DG411

Of course you only get three switches instead of four. What are you working on?

I don't see exactly how that one works. BTW, there are lots of good ways to change the gain of amplifiers, etc., without requiring low Ron switches. As shown in our book for example.

I have a scribbled note which I wrote about 20 years ago in my battered copy of Don Lancaster's 'CMOS Cookbook'. I'll quote verbatim FWIW: "Maplin catalogue recommends that current INTO pins 1, 4, 8 or 11 should be with a voltage drop across switch of max 0.8V (which implies current

Hello Adam,

If you don't want to parallel some, how about using a FET such as the BSS123? About $0.05 in qties but you'd need to keep the gate a few volts above the highest expected signal level.

Regards, Joerg

Hello Jim,

A whole lot. If switching has to be fast they aren't ideal, of course, but it can be somewhat muffled by inverse "injection". Then again, a

For really fast stuff and really low charge injection I use diodes, little toroids and some wire ;-)

Regards, Joerg

Hello Win,

Can't see the previous post (guess it was Adam). I agree, don't think this would work either. If one wanted to get rid of most charge injection using a complementary device in addition can help. Not sure which one would be best since its p-channel brother BSS84 is higher in Cgs. This would be a nice app for one of those Toshiba transistor arrays.

If Adam just wants to change gain one could use a DAC that has an R2R network that could be rendered uncommitted, at least on one side. I had done that once but it's over 15 years ago and I don't remember the DAC. But it was very cheap. Ah, could have been the DAC08 family. It just sat there in the feedback path, the section that goes to GND.

Regards, Joerg

Opps, I missed that part in the 4066 datasheet. I've only ever used the

Joerg, the BSS123 might be a good option. I scribbled down the following;

My max signal amplitude to the BSS123s' will be +-2.5V. This corresponds to Vgs fluctuation of 6+-2.5V or 3.5 to 8.5V. Charge injection and switch rate is not an issue since this is part of a gain setting circuit for DC measurements.

Looks like the 'HC' versions are off on a CD somewhere in archive. But I found the 'LVX' version I did...

Though well past the NDA time limitation I have snipped the schematics out of the final report... I don't want to get sued ;-)

...Jim Thompson