Analog chip supply voltage

Thread Starter

saint_jay77

Joined Oct 19, 2006
26
I had a question about analog chips. Does anyone know of a rule of thumb about supply voltages to analog chips.

#1) can a chip which has a specification from -12 to +12 on the supply be used from 0-12V or 0-24 volt???? This maybe be used from only positive voltage swing.

#2) can a 0 to 5V chip be used in a 0 to -5V. 0 connected to +Vcc and -5V connected to ground??? Needed to get a negative voltage swing!!

#3)Usually is it better to Bias the input or output to get the desired voltage swing???

Thanks.
 

SgtWookie

Joined Jul 17, 2007
22,210
I had a question about analog chips. Does anyone know of a rule of thumb about supply voltages to analog chips.

#1) can a chip which has a specification from -12 to +12 on the supply be used from 0-12V or 0-24 volt???? This maybe be used from only positive voltage swing.
You didn't specify if the chip in question requires -12v to +12v or if that is it's maximum specification. If it requires -12v to +12v, no, you can't run it on 0v to 12v - but you could run it on 0v to 24v. You'd have to either run your signal ground at +12v, or isolate everything else using capacitors.

#2) can a 0 to 5V chip be used in a 0 to -5V. 0 connected to +Vcc and -5V connected to ground??? Needed to get a negative voltage swing!!
Yes, same as above. You can't exceed the input or output max voltage levels without releasing the smoke (which is a bad thing.)

#3)Usually is it better to Bias the input or output to get the desired voltage swing???
"It depends" - upon your application. If you're amplifying a signal considerably, you might be better off biasing it on the output due to the possibility of increasing your signal to noise ratio. Then again, it may significantly simply things to do it on the input.
 

Distort10n

Joined Dec 25, 2006
429
#1) can a chip which has a specification from -12 to +12 on the supply be used from 0-12V or 0-24 volt???? This maybe be used from only positive voltage swing.
Generally, yes. This is especially true for most, if not all op-amps. If you are talking about the ABS MAX ratings then you can use whatever rail voltage you require as long as you do not exceed the ABS MAX rating.
If an op-amp has +/-12 as an ABS MAX supply voltage rating, then that is 24V across the supply. A 0-12V supply rail will not be an issue with the op-amp, but it may be an issue for your design. With single supply op-amps people tend to forget how things change with the input common-mode range, and output swing characteristics.

This is also generally true with most logic devices (gates, MUX, buffers, shift registers, etc). The obvious changes will be with the threshold voltages, since Vcc is now GND. You must take into consideration what is interfacing to this logic, and what the logic is interfacing with.

Data converters may be a little bit more tricky. Generally, they would work, but the question would be how well. You may have to consult the datasheet to see what the expected conversion would be. You would have to switch a lot of rails around to get the converter to behave accordingly. Some data converters have analog supply, digital supply, and external reference. With these particular data converters you would have to switch all the rails relative to each other. I have never seen this done.

#2) can a 0 to 5V chip be used in a 0 to -5V. 0 connected to +Vcc and -5V connected to ground??? Needed to get a negative voltage swing!!
Again, generally yes. Would be easier to get a chip that has a dual supply.
 

beenthere

Joined Apr 20, 2004
15,819
One good rule of thumb is to read the spec sheet and never exceed the absolute maximum voltage difference between Vcc & Vss.
 
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