Analog Switches - Page 1
Forum section: electronics / projects

author: sorin
author_rank: Frequent Contributor
timestamp: April 17, 2012, 08:11:56 am
content: helloI have a questions about analog switchesSo, when the switch is off state, can the analog voltage be higher than she supply voltage??If yes, how many hight??

author: amyk
author_rank: Super Contributor
timestamp: April 17, 2012, 09:08:11 am
content: Try reading the datasheet?

author: sorin
author_rank: Frequent Contributor
timestamp: April 17, 2012, 09:29:01 am
content: Of course I have already read.Intersil datasheethttp://www.intersil.com/data/fn/fn3282.pdfTIhttp://www.ti.com/lit/gpn/ts12a44513

author: Psi
author_rank: Super Contributor
timestamp: April 17, 2012, 10:40:06 am
content: Looking at the 4 protection diodes on the output in the schematic diagram it seems that any switch voltage (S or D) higher that V+ or lower than V- will backfeed onto the IC supply rails.So no, i don't think that will work.From the TI datasheet....Quote

author: JuKu
author_rank: Frequent Contributor
timestamp: April 17, 2012, 12:33:05 pm
content: Relays.

author: sorin
author_rank: Frequent Contributor
timestamp: April 17, 2012, 02:39:18 pm
content: Quote from: JuKu on April 17, 2012, 12:33:05 pmI want to use this in a battery powered, Autorange DMM project so, the relay is not a good idea.

author: amspire
author_rank: Super Contributor
timestamp: April 17, 2012, 02:44:03 pm
content: There has been a new Maxim analog switch that allows the switching inputs to go +/- 25V of the supply rails. The logic can be 3.3V to 5.5V. ON resistance is 1 ohm to 20 ohms. Also the ads for these switches have been often at the top of the Eevblog Forum page recently.http://para.maxim-ic.com/en/search.mvp?fam=swmux_low&hide=270&270=Beyond%20the%20RailsRichard.

author: sorin
author_rank: Frequent Contributor
timestamp: April 17, 2012, 04:04:03 pm
content: Quote from: amspire on April 17, 2012, 02:44:03 pmthank you, but the leakage current of this chip is to hight 250nA compared with 0.5nA (intersil switch).I don't want that the switch work with inputs above the supply voltage, I want just that the switch do don't damaged

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: April 18, 2012, 08:33:48 pm
content: Quote from: sorin on April 17, 2012, 04:04:03 pm250nA too much? Have you noticed 100 Ohm on resistance?Leo

author: sorin
author_rank: Frequent Contributor
timestamp: April 19, 2012, 07:13:30 am
content: Quote from: Leo Bodnar on April 18, 2012, 08:33:48 pmI can compensate the loss in the switch resistance.

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: April 19, 2012, 07:48:42 am
content: Quote from: sorin on April 19, 2012, 07:13:30 amHi sorin,I have not realised you are looking for efficiency rather than precision. Is it AC or DC you are looking to commutate?If you know your signal, why not use regular MOSFETs?Or just protect analogue switch of your choice with TVSes, Zeners, etc?Leo

author: sorin
author_rank: Frequent Contributor
timestamp: April 19, 2012, 09:22:04 am
content: please see the imagethe leakage current of the switch affect the measurement

author: Psi
author_rank: Super Contributor
timestamp: April 19, 2012, 09:43:22 am
content: i don't know what exactly your doing, but there are reed relays which only need 5mA or so.

author: ejeffrey
author_rank: Super Contributor
timestamp: April 19, 2012, 10:00:11 am
content: Quote from: sorin on April 19, 2012, 09:22:04 amThose switches will never see more than a couple of volts. The 1 megaohm input resistor will limit the current to microamps and the input protection circuit will shunt that current to ground in the case where all the switches are "open" and the voltage exceeds the rails. That is the reason for this particular circuit topology which is pretty common in hand held multimeter front ends. The switches can be ordinary analog switches, as long as their on resistance is low and constant.

author: sorin
author_rank: Frequent Contributor
timestamp: April 19, 2012, 10:08:12 am
content: Quote from: Psi on April 19, 2012, 09:43:22 amhttp://www.intersil.com/data/an/an046.pdfpage 3I want to construct a digital multimeter.