Heating operational amplifier OP284FSZ-REEL7

Question

Task: to make a square wave with a frequency of 1 kHz in the voltage range (-12V - +12V), using a PWM signal with voltage (0V-5V).

Circuit:

Originally LM258WYDT (ST) was used as an operational amplifier, it did not heat up, but since it was not from the Rail-to-Rail series, there was a 1.5V drop at the output, which did not allow us to give out a voltage close to 12V. So I decided to switch to Rail-to-Rail, for these purposes I found OP284FSZ-REEL7 (AnalogDevices). After replacing with this amplifier, the value of the output voltage became close to 12V (+-11.85V), but the operational amplifier began to heat up (after 5 minutes its temperature was about 45-60 degrees).

I did not find a short circuit, but noticed that at the output of the voltage divider (R1, R2), instead of 2.5V, the voltage became 4.5V. On the LM258WYDT, this voltage was 2.5V. Perhaps there are elements on this input of the operational amplifier that should lift it?

Unfortunately, at the moment I do not have an oscilloscope and I can not see the output signal.

My suspicions:

1. The amplifier is not designed for such a load or, conversely, it is not enough for it, and it begins to oscillate.
2. Is this an accurate amplifier, perhaps additional elements are needed for its operation?
3. The amplifier is damaged.

Parameters of currents from datasheets:

LM258WYDT

1. Input current: 5mA (DC)
2. Source output current (Isource): 20-60mA
3. Output sink current (Isink): 10-20mA

OP284FSZ-REEL7

1. Supply current: 2.25mA
2. Output current: 10mA

Question: What could be the reason?

Answer 1

It sounds like your amplifier might be damaged. Add bypass capacitors (10 or 100nF ceramic) near each supply pin to ground though, and double check the connections before you conclude that. Make sure the unused op-amp is properly dealt with (eg. a voltage follower with input grounded). The typical < 2.2mA total supply current for the two amplifiers should lead to less than 55mW of dissipation which is something like 8°C rise at the chip and 5°C rise at the case.

What you are observing on the inverting input is a result of the type of op-amp you are using - a super-\$\beta\$ bipolar type. To protect the input transistors against reverse Vbe breakdown, they put diodes across the inputs. That's of little consequence in most op-amp circuits, however you are trying to use it as a comparator.

Note that this particular amplifier does not have series resistance on the inputs, so if you were to short R1 or R2 even momentarily, the high current between the inputs could be enough to damage the op-amp. To prevent this you can add another resistor in series with the input signal but it would be better to use a more appropriate part.