DG509 beyond Vdd

[RES]

Goodday,

Not sure if a DG509 can withstand higher voltages on the input pins while operating at 5V single supply. Want to monitor cell voltages and don't want to waste an opamp on each cell. Datasheet DG509 tells:

• V+ to V- analog signal swing range
• 44 V power supply maximum rating

But:

• Digital Inputs a, VS, VD (V-) - 2 to (V+) + 2 or 20 mA, whichever occurs first

?
Inputs float over each cell. Do inputs DG509 still need protection? (clamp diodes for example?)

Thanks.

[Zero999]

The DG509 has diodes connecting all of its inputs/outputs to +V & -V to protect them from over voltage. It will be fine, as long as the current is limited to a safe level, to protect the diodes. Like any analogue switch it cannot switch signals outside its power supply rails.

[EmmanuelFaure]

Like any analogue switch it cannot switch signals outside its power supply rails.

Actually not "any"!

[Zero999]

Like any analogue switch it cannot switch signals outside its power supply rails.

Actually not "any"!

No, not unless the analogue switch has a built-in charge pump to boost its internal supply voltage.

Look at the schematic of a typical analogue switch:

https://wiki.analog.com/university/courses/electronics/electronics-lab-28

[EmmanuelFaure]

Thanks you. That's not a "typical" analog switch, but a CMOS analog switch.

Using non complementary topology, you can switch voltage well beyond supply voltage. CMOS analog switches are very common (Cheap to manufacture, classic process), but that doesn't mean they're the only solution available.

[Zero999]

Thanks you. That's not a "typical" analog switch, but a CMOS analog switch.

Using non complementary topology, you can switch voltage well beyond supply voltage. CMOS analog switches are very common (Cheap to manufacture, classic process), but that doesn't mean they're the only solution available.

Please provide some example part numbers?

[Kleinstein]

To go really beyond supply one could use optocouplers with FET output,e.g. H11F1 or optomos types.

[Zero999]

An LDR opto-coupler could also be used.
http://www.farnell.com/datasheets/16352.pdf?_ga=1.198329706.47418993.1417808164

[T3sl4co1l]

Thanks you. That's not a "typical" analog switch, but a CMOS analog switch.

What other kinds are there?

[Zero999]

Thanks you. That's not a "typical" analog switch, but a CMOS analog switch.

What other kinds are there?

I wondered that too.

[T3sl4co1l]

Not to be pejorative -- there are other kinds (if not nearly as common, today!).  I'm honestly wondering what you're familiar with.

Tim