EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: init on March 09, 2016, 11:33:13 am
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Hi guys, I am looking for the maximum ratings for a dual supply mode of operation using an INA332 http://www.ti.com/lit/ds/sbos216b/sbos216b.pdf (http://www.ti.com/lit/ds/sbos216b/sbos216b.pdf) . No on page 2, it says that Supply voltage, V+ to V- = 7.5 V, fair enough, the difference between them can't be above this voltage. On page three, under power supply it says that specified voltage range is min:+2.7V and max: +5.5V. Does this mean that the V+ pin must be within this range? What about the negative rail V-, where are its ratings? AM I correct in thinking that a -5V to +5V dual rail is above specs but a -3.3V to +3.3V is within specs?
Sorry for all the questions, just trying to wrap my head around dual supplies.
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If you supply the amp with voltage range of 2.5V and 5.5V between V+ & V-, the amp will operate according to the specifications.
If you exceed the 7.5V, the amp could be destroyed (absolute maximum rating). If you apply more than 5.5V and less than 7.5V the amp would work fine; but it's possible that it doesn't meet some of the specifications anymore.
The power supply voltage is always measured between V+ and V-
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On page three, under power supply it says that specified voltage range is min:+2.7V and max: +5.5V. Does this mean that the V+ pin must be within this range? What about the negative rail V-, where are its ratings?
It means V+ minus V- must be within that range. Circuits have no concept of absolute voltage, voltages in a circuit are all relative. V+ needs to be 2.7-5.5V higher than V-. How either of these voltages relate to the point in your circuit that you arbitrarily choose to call "ground" is irrelevant.
AM I correct in thinking that a -5V to +5V dual rail is above specs but a -3.3V to +3.3V is within specs?
No. You need an amp that's designed to operate correctly at +/- 3.3v (dual supply) or 6.6v (single supply). There's really no difference between a single supply and a dual supply op-amp, which is why most of them list both ratings.
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Hi
One spec missing so far is "common mode input range". That is the range of voltage (relative to V-) that the inputs must stay in. If you go outside this range, odd things happen. Some op amps have "rail to rail inputs". In that case the inputs are OK as long as they are inside the V+ and V- rails. It is never save to *guess* that an amp is rail to rail. You need to check the specs.
Just for the sake of getting it all said: The same thing applies to the output of the amp. Here you also need to check the output current they will handle as they get to whatever limit is mentioned. If you load is not 1uA then the sated spec (at 1uA load) may not apply to you.
Bob