Using Analog Switch ICs? - Page 1
Forum section: electronics / beginners

author: theatrical scene
author_rank: Contributor
timestamp: January 15, 2019, 03:15:29 am
content: Super basic question, I'm using a MC14016 quad analog switch (https://www.onsemi.com/pub/Collateral/MC14016B-D.PDF) and from reading the datasheet it isn't immediately obvious wondering whether the 'inputs' and 'outputs' are indeed bilateral/bidirectional in that I could feed in a voltage from the output side and read it from the input side or is there an internal diode-like structure which means current can only flow one way?

author: amyk
author_rank: Super Contributor
timestamp: January 15, 2019, 04:29:58 am
content: Yes. They are internally constructed as a CMOS transmission gate so they are bidirectional.https://en.wikipedia.org/wiki/Analogue_switch.

author: theatrical scene
author_rank: Contributor
timestamp: January 15, 2019, 04:46:13 am
content: Thanks, are the 'in' and 'out' markings used on the datasheet generally irrelevant/to be used as a guide then in this case?

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: January 15, 2019, 05:34:33 am
content: Irrelevant.Sent from my iPhone using Tapatalk

author: Zero999
author_rank: Super Contributor
timestamp: January 15, 2019, 11:02:50 am
content: Yes, look at the internal schematic for an analogue switch.https://en.wikipedia.org/wiki/Transmission_gate

author: MrAl
author_rank: Super Contributor
timestamp: January 15, 2019, 06:34:03 pm
content: Hi,When i worked in the industry i had to use an analog switch for several different designs in power electronics control circuits.However, probably the most interesting case was when i did a hobby circuit using analog switches.This circuit was a membrane keyboard/computer interface.What i had to do was have the computer read and activate EVERY membrane key switch and associated LED indicators on another computer that was dedicated to playing chess. So we had the 64 keys for each chess board square plus some more for normal control and also some 8 LEDs that had to be sensed.The analog switches came into play when the host computer wanted to activate a chess board square or one of the control switches. The chess computer would scan each square using a multiplexing technique, and so to 'press' a square using the host computer the square's switch had to be bidirectional. The analog switch allowed this because it can pass current in either direction through the internal 'switch'. So the host computer was able to take complete control of the dedicated chess computer, both in detecting the game being played by humans and also allow playing back that game right on the chess board using the associated LEDs to indicate each move.So yes analog switches can pass current in both directions. The things to watch out for are bandwidth and 'contact' resistance. The switch series resistance varies with supply voltage on the ones i used which were CMOS.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 15, 2019, 06:41:40 pm
content: A point to watch is that the voltage at the switch terminals has to be within the supply range of the CMOS switch chip.

author: Benta
author_rank: Super Contributor
timestamp: January 15, 2019, 09:57:50 pm
content: Apart from that, the MC14016 is ancient, obsolete and superceded by the MC14066.

author: theatrical scene
author_rank: Contributor
timestamp: January 15, 2019, 10:37:10 pm
content: Oh thanks for the heads up Benta. The part looks pin compatible so I could just drop it into the designOn another note, how do you generally find out whether parts are superseded from their datasheets?

author: Zero999
author_rank: Super Contributor
timestamp: January 15, 2019, 11:41:50 pm
content: There's also the 74HC4066, which has a much lower on resistance and wider bandwidth, than the 40xx varieties, but has an operating voltage range of 2V to 10V, rather than 3V to 18V.https://assets.nexperia.com/documents/data-sheet/74HC_HCT4066.pdf

author: Kleinstein
author_rank: Super Contributor
timestamp: January 16, 2019, 05:25:27 pm
content: Quote from: theatrical scene on January 15, 2019, 10:37:10 pmThe datasheets seldom show replacement parts when the part gets obsolete. The last update on the DS is usually just the obsolete info.If not too old one can often still find a general info page for the part at the manufacturer, where they usually also show a replacement. Other wise just search for a new part - quite often new parts keep the pin-out if there are older parts they can replace.The 4016 presumably has less charge injection (and maybe typical leakage). So the 4066 is not always better. The 4066 and similar are cheap parts from the logic series. For higher requirements there are higher specs special switches, like DG211 and many similar.