Have a question about ADCs or DACs? Ask our Expert, Nick Gray

Hi Nick,

I have read the tutorial document you had previously linked to a user enquiring about analog switches.

Perhaps you can help me understand something basic about the ADG419BZ analog switch. What is the maximum voltage that can be applied to the output pins (s1 and s2)? What would this information be listed under in the datasheet?

Also, it says that the device can operate from a 12V single supply but can be remain functional to voltages as low as 5V. Does this mean I can apply 5V to the VDD pin?

If you can help me on these points, I would be very grateful.

Regards

Rachel

Hi Nick,

I have read the tutorial document you had previously linked to a user enquiring about analog switches.

Perhaps you can help me understand something basic about the ADG419BZ analog switch. What is the maximum voltage that can be applied to the output pins (s1 and s2)? What would this information be listed under in the datasheet?

Also, it says that the device can operate from a 12V single supply but can be remain functional to voltages as low as 5V. Does this mean I can apply 5V to the VDD pin?

If you can help me on these points, I would be very grateful.

Regards

Rachel

Hi, Rachel –

I am very happy to answer your  question on analog switches.

The ADG419 is an analog switch from Analog Devices and is their version of the DG419 from Vishay Siliconix. The letters at the end of the device type indicate the type of package, temperature range and how the device is packaged (tape-and-reel, etc.).

Most specifications for the “Operating Conditions” of electronic components can be found in the specification tables of the data sheet. However, analog switches often do not have input range on their data sheets. This is because it is assumed that the input can be anywhere within the negative and positive supply voltages of the product. Often the negative supply voltage is zero Volts. If you look at Figure 6 on page 7 of the ADG419 data sheet, you will note that, for a single supply, the curves show the “On” resistance from 0V to the voltage of the supply. This tells you that you can go to these limits. Figure 3 on the same page tells you that you allow the input voltage to go down to the negative supply voltage and up to the positive supply voltage. What may not be obvious from these graphs is that the input (or output) voltage is on the horizontal axis. VS is the voltage on either “S” input and VD is the voltage on the “D” input.

Note that these figures indicate that the “on” resistance, which is the resistance between input and output, changes as the input voltage changes. This can lead to signal distortion if you are not careful. This is true of all analog switches.

Yes, you can use this analog switch with a single 5V supply applied to the VDD pin, but from Figure 6 you will note that the “on” resistance that ranges between less than 60 Ohms to above 70 Ohms. This may or may not be a problem in your application. The Vishay Siliconix DG419 with a 5V supply has an “on” resistance that varies between a little over 30 Ohms to less than 50 Ohms, as seen in the plot at the top left of page 5 of that data sheet. The variation is larger than the Analog Devices’ product, but has a lower value. Which would be better for you will depend upon just what you are doing with it. If you are putting a fairly high quality AC signal through it (like audio, for example), I would prefer the analog device product because it has less variation (and percentage variation), so would give you less distortion (also, larger signals would mean more distortion). If you are passing only DC through it, I would prefer the Vishay Siliconix product because you would get less voltage drop across it.

I do hope that this answers your question. Let me know if you need anything else.

Nick