Using Multiplexer 74HCT4053 - Page 1
Forum section: electronics / beginners

author: xoom
author_rank: Regular Contributor
timestamp: July 28, 2016, 06:01:01 pm
content: Hi, i want to use multiplexer chip for ADC. To measure voltage and current. ADC is LTC2420. As im using only one switch in it (its a Triple 2-channel multiplexer) i don't know what to do with others (datasheet not tells anything about unused pins). Can they all be grounded? As im using 2Y0, 2Y1, 2Z and S2 pins other select pins also can be grounded?Thank you.

author: singapol
author_rank: Frequent Contributor
timestamp: July 28, 2016, 06:35:55 pm
content: The general guideline is unused cmos outputs can be left floating but unused inputs must be connected to VCC(power supply) or ground.Questions about cmos ic:http://toshiba.semicon-storage.com/ap-en/design-support/faq/logic.htmlDesigning with logic:www.ti.com/lit/an/sdya009c/sdya009c.pdfhttps://www.fairchildsemi.com/application-notes/AN/AN-77.pdfhttp://electronicdesign.com/boards/save-power-managing-unused-cmos-io-pins

author: xoom
author_rank: Regular Contributor
timestamp: July 29, 2016, 08:03:12 am
content: Yep. i tryed on scope how signal looks on floating select pins channels. It looks like WAV to MP3 conversion(its picking 50Hz and swiching on and off

author: xoom
author_rank: Regular Contributor
timestamp: July 29, 2016, 10:08:14 am
content: Anyone can tell is it good layout for ADC or can give some advises how it can be improved?

author: ebclr
author_rank: Super Contributor
timestamp: July 29, 2016, 10:25:39 am
content: Maybe is to late but this can be bougthhttp://www.ti.com/lit/ds/symlink/ads1226.pdf

author: JPortici
author_rank: Super Contributor
timestamp: July 29, 2016, 10:27:14 am
content: The Selector input is a CMOS digital input and as such it must be connected to a digital 0 or 1, so to VCC or GND.I guess you could leave the analog channel floating, but i would ground every pin just to be sure nothing gets picked up ann injected to other channelsQuote from: xoom on July 29, 2016, 08:03:12 amHuh?

author: xoom
author_rank: Regular Contributor
timestamp: July 29, 2016, 10:44:03 am
content: Quote from: ebclr on July 29, 2016, 10:25:39 amI already have that ADC so not planing to buy anotherQuote from: JPortici on July 29, 2016, 10:27:14 amS2 will be connected to Atmega.. im just thinking now about analog part (ground plane and voltage inputs, also VCC)O.T. Analog sound to digital soundit just stuck in my memory when i seen similar image with that presentation

author: Ian.M
author_rank: Super Contributor
timestamp: July 29, 2016, 10:54:53 am
content: Unless charge injection and stray capacitance are serious issues, I'd simply wire all three '4053 switch sections and their control inputs in parallel for lower on resistance.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 29, 2016, 04:17:48 pm
content: With the LTC2420, the GND layout could be critical. As the HC4053 does not use a lot of current the layout is still OK. One might want a capacitor to GND from the input of the LTC2420.The trimmer in the circuit looks a little strange - usually one would use numerical adjustment instead of a drifting analog trimmer.