Overheating in OPA549

Hello Pedro,

Can you please provide oscilloscope shots of the input and output waveforms? Having a resistor in the feedback of the device may cause a stability issue, I recommend changing R5 to 0ohms. For more information on why having a resistor in the feedback might cause a stability issue check out our TI Precision Lab videos on Stability and the blog Resistors in the feedback of a buffer: Ask Why!.

Also, the OPA549 requires the tab of the device to be connected to V- (ground in your case). Is the tab connected to V-?

-Tim Claycomb

Good evening Mr Claycomb, thanks a lot for helping me.

No, I did not have the tab of my device connected to ground, but, I did it. The tab is connected to ground now.

About the resistor, I put a jumper.

I did some test:

I am using now as input DC signals (5v,12v and ground)

My circuit is a buffer in single supply, using 24v.

I measured voltage in all my pins, using as input all about mentioned.

I have 23,5v in pin 4 (IN+) even though I applied 12v, 5v or ground and the output is always about 23v.

For testing, I applied 0v(ground) to pin 9 (E/S) normally I would disable the output, but the output is equal, about 23v.

What do you think?

Thanks

I saw some mistakes. Pin 3 was unconnected.

I did the test again with single supply 12V, (Tab and pins 5,6,7 and 8 to ground)

I always measured output (pin 1 and 2) 160mV  even though I change input+ (pin 4) (ground, 5V or 12V).

In E/S pin (pin 9) I have 9,2V, I connected it to ground and I had the same 160mV in the output.

Do you think My Op Amp is damaged?

Thanks

Hello Pedro,

It is possible that the device has been damaged. If you believe you have damaged the device, I recommend changing out the device as it can save a lot of time.

To enable the output of the OPA549 the E/S pin must be driven high (at least 2.4V above Ref) or be left floating. Grounding the E/S pin will disable the output which might explain why you are seeing only 160mV on the output.

I recommend rewiring your circuit using the circuit you provided in your original post and leaving E/S pin open and a jumper or 0 ohm resistor across R5 like you mentioned.

-Tim Claycomb

Hi, Mr Claycomb

I could buy a new one, it was not easy, but I did it.

I changed my OPA549, effectively, It was broken.

Now, I am using my OpAmp in single supply 12V in buffer configuration, using a 0 ohms (R5).

It works normally, It does not overheat, however, I have a problem that I would like to fix.

I have a high offset voltage at the output 660mV when I connect my input (pin 4 = IN+) to ground

Could I reduce the offset voltage in my OpAmp?

I tried putting -5V in my input (pin 4) and my output was 10mV, It was really good, but Is there another way to reduce that offset voltage?

Is it normal that I get high offset voltage in a voltage follower configuration?

I wa thinking in the next diagram.

Thanks a lot

Hi Pedro,

Using the OPA549 with a 12V single supply the minimum input common mode voltage is -.2V. Therefore applying a -5V input is outside the linear operation of the amplifier.

The typical output swing is 0.1V from the negative rail with an 8 ohm load connected to the negative supply. Therefore when you connect IN+ to ground, the output of the amplifier attempts to go to 0V. However, the output can only swing to 0.1V. Therefore the output swing limitation of the amplifier is being violated and the amplifier is outside of the linear operating region when the IN+ pin is grounded.

I recommend watching our TI Precision Lab videos on input and output limitations to fully understand why the amplifier is outside of the linear operating region.

Using the configuration you show will still violate the input common mode with a -5V input.

Thank you,

Tim Claycomb