DG509 beyond Vdd - Page 1
Forum section: electronics / projects

author: RES
author_rank: Regular Contributor
timestamp: September 08, 2016, 12:25:46 pm
content: 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 ratingBut:• 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.

author: Zero999
author_rank: Super Contributor
timestamp: September 08, 2016, 09:15:05 pm
content: 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.

author: EmmanuelFaure
author_rank: Regular Contributor
timestamp: September 08, 2016, 09:26:28 pm
content: Quote from: Hero999 on September 08, 2016, 09:15:05 pmActually not "any"!

author: Zero999
author_rank: Super Contributor
timestamp: September 08, 2016, 09:34:10 pm
content: Quote from: EmmanuelFaure on September 08, 2016, 09:26:28 pmNo, 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

author: EmmanuelFaure
author_rank: Regular Contributor
timestamp: September 11, 2016, 01:07:41 pm
content: 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.

author: Zero999
author_rank: Super Contributor
timestamp: September 11, 2016, 02:03:57 pm
content: Quote from: EmmanuelFaure on September 11, 2016, 01:07:41 pmPlease provide some example part numbers?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 11, 2016, 05:18:05 pm
content: To go really beyond supply one could use optocouplers with FET output,e.g. H11F1 or optomos types.

author: Zero999
author_rank: Super Contributor
timestamp: September 11, 2016, 08:01:51 pm
content: An LDR opto-coupler could also be used.http://www.farnell.com/datasheets/16352.pdf?_ga=1.198329706.47418993.1417808164

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 12, 2016, 01:17:13 am
content: Quote from: EmmanuelFaure on September 11, 2016, 01:07:41 pmWhat other kinds are there?

author: Zero999
author_rank: Super Contributor
timestamp: September 12, 2016, 08:33:19 pm
content: Quote from: T3sl4co1l on September 12, 2016, 01:17:13 amI wondered that too.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 13, 2016, 04:47:17 am
content: Not to be pejorative -- there are other kinds (if not nearly as common, today!). I'm honestly wondering what you're familiar with.Tim