SPDT Analog Switch IC - Page 1
Forum section: electronics / beginners

author: Ray Hall
author_rank: Newbie
timestamp: November 03, 2017, 09:38:51 am
content: Hello Everyone,I have test equipment that uses mechanical SPDT toggle switches. My new design will use all SMD components. I have spent many days looking on Mouser and Digikey for a IC that will do the same job. I have looked at solid state relays and analogue and digital switches. The only one I could find that looks suitable is the ADG436BRZ. It is a 2 x SPDT. I would prefer to use something in a smaller package and more channels. The maximum current at 14 volts is 100 mv.My project uses a 5v power supply and the Freescale S12XE 16 bit micro.This circuit shows what I want to replace, with a IC.Ray.

author: ebclr
author_rank: Super Contributor
timestamp: November 03, 2017, 09:47:05 am
content: A good variety to choose fromhttp://www.ti.com/switches-multiplexers/analog/products.html#p1059min=0;5&p1059max=5;36

author: Zero999
author_rank: Super Contributor
timestamp: November 03, 2017, 10:00:53 am
content: Quote from: Ray Hall on November 03, 2017, 09:38:51 amThat makes no sense. Current is measured in amps, not volts.If the current is 100mA, then use a MOSFET. Analogue switches are generally only designed for switching small signals, <1mA, not milliamps. There are some higher powered headphone analogue switches available, but even then the maximum voltage is under 6V and current rating <100mA.What's connected to the common terminal of the switch? Please post the full schematic.

author: Ray Hall
author_rank: Newbie
timestamp: November 03, 2017, 09:15:31 pm
content: QuoteMy brain was not connected to fingers when typing. It was meant to be 100 mA not 100 mV.

author: Zero999
author_rank: Super Contributor
timestamp: November 03, 2017, 10:45:35 pm
content: Quote from: Ray Hall on November 03, 2017, 09:15:31 pmThen an analogue switch is not the correct component for the job, as mentioned above.

author: Ray Hall
author_rank: Newbie
timestamp: November 05, 2017, 08:45:33 am
content: QuoteHere is the schematic related to the switches. This schematic shows three ADG436BRZ (S9,S10,S11) switches. This I want to replace with something I am sure will do the job. The circuit generates two square wave signals. The one called HALL is 0 to 5 volt. The RELUCTOR is a zero crossing from -5 to 18 volt.Thank you.

author: Ray Hall
author_rank: Newbie
timestamp: November 06, 2017, 09:11:08 pm
content: QuoteHere is the schematic related to the switches. This schematic shows three ADG436BRZ (S9,S10,S11) switches. This I want to replace with something I am sure will do the job. The circuit generates two square wave signals. The one called HALL is 0 to 5 volt. The RELUCTOR is a zero crossing from -5 to 18 volt.You say to use a MOSFET. To my thinking I would need two a P and N. Any idea how to use them. If the question is too hard for the beginners section, should I post the question elsewhere.Ray.

author: rstofer
author_rank: Super Contributor
timestamp: November 06, 2017, 09:40:31 pm
content: If PB0..3 are inputs to a uC, the current will be in a low number of microamps, nowhere near 100 mA.The reluctors have a driving impedance of, at minimum, 1k. For a 10V supply, the most they could send would be 10 mA. But send it where? The uC input is microamps.The hall devices don't have a series resistor to limit current. Why couldn't they have the same 1k source impedance that the reluctors have. But still the same argument, where are they going to send the current?More important than the last two items is the first. If those are uC inputs, you don't have very much current to be concerned about and the source impedance is unimportant.You need to get this straight before you look at analog switches. Make sure you know what you are driving just in case the device won't switch at such low currents.

author: Ray Hall
author_rank: Newbie
timestamp: November 07, 2017, 09:19:15 pm
content: QuoteThey are the inputs from the micro controller. I cannot see what they have to do with the switching current for S1A,S1B and D1.QuoteThe reluctor signals go to the crankshaft and camshaft signal inputs on a engine management ECU. Admitted...these take nothing to drive.QuoteThe engine management ECU that use HALL effect sensors often have around 1k to 2k2 pullup resistors. While I may not need 100mA I would rather not be on the limit of the switches.QuoteI contacted Analog.com and they recommended the ADG1436. This will drive up to 600 mA (over kill in my case) and will work with the zero crossing signals. Add to that it is in a small package that I was lookimg for.Ray.