SPDT Analog Switch IC

[Ray Hall]

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.
 

[ebclr]

A good variety to choose from

http://www.ti.com/switches-multiplexers/analog/products.html#p1059min=0;5&p1059max=5;36

[Zero999]

The maximum current at 14 volts is 100 mv.

That 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.

[Ray Hall]

That makes no sense. Current is measured in amps, not volts.

My brain was not connected to fingers when typing. It was meant to be 100 mA not 100 mV.

[Zero999]

That makes no sense. Current is measured in amps, not volts.

My brain was not connected to fingers when typing. It was meant to be 100 mA not 100 mV.

Then an analogue switch is not the correct component for the job, as mentioned above.

[Ray Hall]

What's connected to the common terminal of the switch? Please post the full schematic.

Here 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.

[Ray Hall]

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.

Here 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.

[rstofer]

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.

[Ray Hall]

If PB0..3 are inputs to a uC, the current will be in a low number of microamps, nowhere near 100 mA.

They are the inputs from the micro controller. I cannot see what they have to do with the switching current for S1A,S1B and D1.

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 reluctor signals go to the crankshaft and camshaft signal inputs on a engine management ECU. Admitted...these take nothing to drive.

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?

The 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.

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.

I 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.