OP275 is having reliable issue

Hello Preethamshetty,

Can you share more details about the performance issue that you have encountered? What specific problem have you encountered?

Best regards,
Paul

Hi Paul, 

The problem that I encountered is for example if we give 5v input the output is around 4.7v, when using OP275 as a buffer

Sometimes we also give 32V as input.. We thought because of 32V input it is degrading the performance. 

Can you please tell me the Vcm range of OP275 when supplying +35V and -5. 25V? 

If Vcm is not the problem then please let me know what is causing the issue.. Meanwhile I'll share u the snap of schematics

Regarda

Preetham

Hello Preethamshetty,

Were the supplies still +35V (+Vs) and -5.25V (-Vs), respectively, when the input is 5V? Have you measured the input voltage using a voltmeter and confirmed if the input signal level is really 5V? May I also ask if the change in Vin from 32V to 5V happened immediately?

In addition, I just would like to point out that having an input voltage of 32V will most likely overdrive the part and force it to saturate. As indicated on the part's data sheet, it has an input voltage range head room and foot room of about 4.5 V from its supplies:

Which means, if your supplies are +35V and -5.25V respectively, your IVR range should only fall within about -0.75 to +30.5 V.

Best regards,
Paul

Hi Paul,

The supply is still the same when the input is at 5V and also measured the input voltage through voltmeter which is 5V. The change from 5 to 32V will happen immediately

In our case saturation is not happening. Because we assembled 10 boards out of which 6 are working without any issues. in 4 boards different observations are seen. In couple of boards the opamp is completely gone bad and started working after replacing. in latest 2 boards the voltages are getting divided. Here is the snapshot of the path in which opamp is used. Please refer both the pages in the below doc

PDF

Regards

Preetham

Hello Preethamshetty,

Just wanted to clarify, when your input is +32V, you are still getting a +32V output, right? This is quite interesting. Ideally, the output voltage should clip/saturate at around +30.5V because your input is already outside its specified input voltage range, and you are most likely overdriving the part. Both the +32V and 5V input were DC, right?

Right now, I'm currently thinking if the part's absolute maximum junction temperature of +150C is being hit when the input is 32V. Can you provide me the following:

- Oscilloscope shots or voltmeter pics of the op amp's output when the input is 32V.
- Supply current readings when the input is 32V. (Both +Is and -Is). 
- Ambient temperature (Ta) of your setup
- If you also have the time, can you measure the output current using an ammeter when the input is also 32V? Thanks.

By having these data, we can compute for the part's total power dissipation and determine the junction temperature. In case that the junction temperature hits or exceeds 150C, then, it is most likely the root cause of the issue.

Best regards,
Paul

Hi Paul,

Ill give you the details.. In the meantime can you please suggest a part suitable for our  requirement

Thanks and regards

Preetham

Hello Preethamshetty,

Can you share what other critical specifications/electrical characteristics (like bandwidth, input bias current, offset current and voltage, noise, etc.) do you want for your application? Getting the data that I've requested in my previous reply will also help us find a suitable replacement for the part.

Best regards,
Paul

Hi Paul, 

I need a Opamp with low noise figures and low offset current and low offset voltage and low input bias current hence I went with OP275 (audio amplifier). The noise figures and offset values should be equal or less than that of OP275

Bandwidth should be more than 1.5MHz and it should support +35V and -5.25V power supply and should support input from 0 to 32V.

I'm collecting the data that you have asked for. Probably by Monday ill give the details

Regards

Preetham

Hello Preethamshetty,

Thank you for this information. For the testing, you can just get the data of the stage shown below. I'm assuming you have used both of OP275's channels here:

Sorry if I forgot to ask, assuming the stage above is configured using a single IC package, is there a time where amplifier1 and amplifier2 above both have a 32V input? Does amp1 and amp2 always have the same input voltage? 

Data Needed: 

- Oscilloscope shots or voltmeter pics of amp1 and amp2's output 
- Supply current readings. (Both +Is and -Is). 
- Ambient temperature (Ta) of your setup
- Output Current of amp1 and amp2. 


Best regards,
Paul