Had trouble understanding datasheet of opamp TL072 as voltage follower

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ashokraj

Joined Feb 1, 2018
79
I am working on TL072 IC, I need expertise of experienced people in the following:
  1. 1. In page 10 of data sheet the common mode voltage is mentioned as VCC- +4 to VCC+ does it mean the allowed input range of inputs are +4 to Vcc+ ( could be 12V or 15V ) or does the range mean allowed input voltages are, lets say rail voltages are +12V and -12V so the allowed input range is -12+4 to 12V i.e., -8 to 12V ??
  2. 2. I need to wire this IC as voltage follower/unity gain circuit, is it mandatory to use 100pF or I can change to 2.2uF ( Page 25).
  3. 3. Page 29, 8.3 as per the data sheet there is no -vcc and it is connected to ground so practically if i give -vcc instead of connecting it to ground does the circuit function or it works abruptly ???? . also, it is mentioned in the data sheet as follows:
  4. Input voltage must be within the recommended common-mode range, as shown in Recommended Operating
    Conditions. The valid common-mode range is 4 V to 12 V (VCC– + 4 V to VCC+).
4. IF I need to wire this as voltage follower should i give dual supply or single supply only?
again the same question as point 1.
 

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OBW0549

Joined Mar 2, 2015
3,028
1. In page 10 of data sheet the common mode voltage is mentioned as VCC- +4 to VCC+ does it mean the allowed input range of inputs are +4 to Vcc+ ( could be 12V or 15V ) or does the range mean allowed input voltages are, lets say rail voltages are +12V and -12V so the allowed input range is -12+4 to 12V i.e., -8 to 12V ??
-8 to 12V is correct. The input common mode range is always relative to the voltages on the op amp's supply terminals.

2. I need to wire this IC as voltage follower/unity gain circuit, is it mandatory to use 100pF or I can change to 2.2uF ( Page 25).
Don't ever connect ANY capacitance to the op amp's output! That 100pF capacitor shown in the diagram(s) is not there to indicate a capacitor that you must connect to the output; it's there to indicate the load conditions under which the op amp parameters are measured by the IC manufacturer. Don't connect a capacitor to the output.

3. Page 29, 8.3 as per the data sheet there is no -vcc and it is connected to ground so practically if i give -vcc instead of connecting it to ground does the circuit function or it works abruptly ???? . also, it is mentioned in the data sheet as follows:
Input voltage must be within the recommended common-mode range, as shown in Recommended Operating
Conditions. The valid common-mode range is 4 V to 12 V (VCC– + 4 V to VCC+).
Again: input common mode range is ALWAYS relative to the voltages on the op amp's supply terminals. If the Vcc- terminal is connected to ground, the input CMR will be from +4V up to Vcc+. If Vcc- is connected to a negative supply, the input CMR will extend from 4 volts above that supply up to Vcc+.

4. IF I need to wire this as voltage follower should i give dual supply or single supply only?
again the same question as point 1.
That depends entirely on the range of your input signal. If your input will never go more negative than +4V, you can simply ground the Vcc- terminal; otherwise you must provide an appropriate negative supply.
 

Audioguru again

Joined Oct 21, 2019
288
Like most opamps, when a certain amount of capacitance to ground is connected to the output, especially when the negative feedback is high reducing the gain to 1, the output will oscillate at a high frequency. The TL072 can have no more than 100pF which is a piece of shielded audio cable about 1m long. If a longer cable is needed then connect a 100 ohm resistor from the opamp output to it.

The TL07x and TL08x have a problem when an input voltage becomes within 4V from its negative supply called "Phase Inversion" which causes its output voltage to suddenly go as high as it can.

The minimum recommended supply for a TL07x is 10V but I have used many powered from a 9V battery and they worked fine. Any opamp can be powered from a single positive supply (instead of using a dual-polarity supply) if its non-inverting input is biased at about half the supply voltage and input, output and feedback-grounding coupling capacitors are used like this:
 

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