At which voltage does this switch become closed?

Question

At which voltage does this switch become closed?

http://www.analog.com/en/switchesmultiplexers/analog-switches/ADG801/products/product.html

As expected I am using the NO version. I am under-educated on CMOS switches and don't understand when the switch actually becomes activated and closes.

Answer 1

Read the data sheet. You will need it before you can use the switch.

With Vcc of 5 volts, VinH is 2 volts

VinL is 0.8 volts

Which means it turns on for a voltage less than 2 volts, and turns off for a voltage higher than 0.8v

You do realize you can only switch low voltage signals with this?

http://www.analog.com/static/imported-fi...

Answer 2

For the '802 (NO version), the switch is guaranteed closed at 0.8V or less. It is guaranteed open at 2.0V or more. The '801 (NC version) is opposite, open at ≤0.8V and closed at ≥2.0V. These parts have TTL inputs, so having the input between these states could go either way, or partway open, and is not allowed except for brief times to switch. Thus, driving with a comparitor is a good way to do it.

DataSheet

The Digital Input section indicates VINL is 0.8V, VINH is 2.0V. That tells you the stuff above about the input voltages.

It think you got the wrong part, the NO/NC terminology is very confusing. Fortunately, figure 17 on page 10 shows the parts functions exactly. You can see that the output does the same as the input on the '801 part, while it's opposite on the '802 part.

These is nice parts, but are limited to 400mA steady state; depending on the package and the way it is mounted on the PCB, the parts may be limited to less than that by the temperature (see thermal resistance on the datasheet).

General

I prefer to use MOSFET's for switches. See

http://answers.yahoo.com/question/index;...

Of course, MOSFET's also have datasheet values that you have to verify to assure the part is suitable...