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4066 operation
4066 operation
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Old 23rd August 2019, 06:01 AM   #1
audiostrat is offline audiostrat  Greece
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Default 4066 operation

Hello,

I am posting to ask a simple question about the common analog switch 4066.

Can the power supply (and the control signals) to this IC be completely isolated from the analog path that will be injected into the switch I/O? No ground connection between them. In other words, can it be used as a "relay" where the "coil" circuit (IC power supply) has nothing to do with the switching path.
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Old 23rd August 2019, 06:10 AM   #2
abraxalito is offline abraxalito  United Kingdom
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No. If you want isolation between the control side and the analog signal path then you could use something like this : TLP592A(F) Toshiba | Mouser


Its more expensive and slower to switch, but has a much lower on-resistance.
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Old 23rd August 2019, 10:03 AM   #3
Kay Pirinha is offline Kay Pirinha  Germany
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And the signal voltages mustn't exceed the voltages at both the 4066's negative and positive supply pins.
Best regards!
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Old 24th August 2019, 11:10 AM   #4
Mark Tillotson is offline Mark Tillotson
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These analog switch chips use CMOS transmission gates, which are not isolated in any way.
CMOS chips have anti-static protection diodes on the pins, so the voltages on any pin must stay without the supply rails at all times.


There are many modern analog switch chips with far superior performance to the original CD40xx series versions, but they all use transmission gates.
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Old 24th August 2019, 08:53 PM   #5
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by Mark Tillotson View Post
These analog switch chips use CMOS transmission gates, which are not isolated in any way.
CMOS chips have anti-static protection diodes on the pins, so the voltages on any pin must stay without the supply rails at all times.


There are many modern analog switch chips with far superior performance to the original CD40xx series versions, but they all use transmission gates.
Care needs to be taken with voltages in and out of IC's.
I did a USB project and accidentally drove an output 5 volts into a another IC powered off 3v3. The PC went nuts and said it was closing down to stop damage to it !
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Old 24th August 2019, 09:10 PM   #6
MarcelvdG is offline MarcelvdG  Netherlands
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Originally Posted by abraxalito View Post
No. If you want isolation between the control side and the analog signal path then you could use something like this : TLP592A(F) Toshiba | Mouser


Its more expensive and slower to switch, but has a much lower on-resistance.
But compared to a 4066, it has a much larger off-state capacitance, so depending on the circuit, some treble may leak through when it is off. In any case, there are other optocouplers with MOSFET output, the trick is to find the best compromise between on resistance and off capacitance for the application.
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Old 24th August 2019, 09:36 PM   #7
MarcelvdG is offline MarcelvdG  Netherlands
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Originally Posted by nigelwright7557 View Post
Care needs to be taken with voltages in and out of IC's.
I did a USB project and accidentally drove an output 5 volts into a another IC powered off 3v3. The PC went nuts and said it was closing down to stop damage to it !
Again depending on the application, the main risk is probably latch-up. Most ICs (including the 4066) are full of parasitic thyristors between supply and ground. An input or output voltage above the positive supply or below the negative supply can trigger these thyristors. Nowadays ICs are usually designed not to trigger as long as the input or output current stays below 100 mA, but I don't know what the limit used to be when the 4066 was designed.

If a parasitic thyristor should get triggered, the IC will burn out unless the supply has a low current limit and no big decoupling capacitors. You often see 4000-series electronic switches being supplied by resistors and Zener diodes, that's probably a good idea if there is any risk of the input going above the positive or below the negative supply.
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Old 24th August 2019, 11:40 PM   #8
nigelwright7557 is offline nigelwright7557  United Kingdom
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The 4066 has been around for a very long time.
We used them in 1981 in a Prestel adaptor (forerunner to the internet)
The 4016 was a similar device.
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Old 25th August 2019, 03:24 AM   #9
davidsrsb is offline davidsrsb  Malaysia
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Originally Posted by MarcelvdG View Post
But compared to a 4066, it has a much larger off-state capacitance, so depending on the circuit, some treble may leak through when it is off. In any case, there are other optocouplers with MOSFET output, the trick is to find the best compromise between on resistance and off capacitance for the application.
There is a reason that we still use signal switches and relays in the 21st Century
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Old 25th August 2019, 03:34 AM   #10
synonymous is offline synonymous  United States
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If you are looking to mute a signal, consider grounding rather than an analog through switch.
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