OPA549: OPA549 Permanent Offset Error

Hello Yakup,

This level of offset change sounds serious. Would it be possible for you to provide the schematic for your OPA549 circuit, along with power supply, load and input and output signal information? Also, since the OPA549 devices are dissipating large amount of power I need to see the thermal arrangements you have provided such as heat-sinking, thermal connection method and device mounting information.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Thomas,

Thanks for your answer. I have one master opamp and 5 slave opamp(opa549). 5 slave opamp is parallel. I send my slave opamp schmatic and master opamp schmatic. In addition this schmatics I add 10uF and 100nF(parallel) slaveopamp's +Vs and -Vs. And I add  7,5R  33uF(series) output of slave opamps like snubber.

Input voltage= +-6V(After master opamp -+30V) 

Supply Voltage= +-30V

Load= 0,6ohm coil

For Thermal Dissipating I assambly all opamp cooler

Thanks.

Master Opamp Schmatics

Slave Opamp Schmatics

Hello Yakup,

I don't see anything incorrect about the master or slave Op amp circuits. However, there is one operating aspect of the circuit that is outside the normal linear operating range of the OPA549. 

The input to the master amplifier is +/-6 V, which is increased to nearly +/-30 V at its output. The +/-30 V is applied to the OPA549 non-inverting inpuy which as a rated common-mode voltage (Vcm) range of about (V-) - 0.1 V on the low end, but about (V+) – 3 V to (V+) – 2.3 V on the high end. Since the slave OPA549 amplifiers are being powered by +/-30 V, a +/-30 V input exceeds the positive Vcm limit. Initially, the OPA549  may tolerate it, but I don't know if that is okay after hours. The ABSOLUTE MAXIMUM RATINGS Input Voltage Range is (V–) – 0.5V to (V+) + 0.5V so you are close. Note 1 under the table states "Exposure to absolute maximum conditions for extended periods may degrade device reliability."

Exceeding the Vcm range severely degrades the dc and ac characteristics and possibly something is happening to the Op amp when operated in that non-linear input region.

You responded "For Thermal Dissipating I assambly all opamp cooler." If you could provide more information about the assembly process such as how the OPA549 TO-220 package tabs get torqued down to the cooler and to what toque specification that is accomplished that would be helpful. It is possible to torgue the tab down with so much force that the amplifier die inside the package becomes physically and electrically damaged.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Thomas,

Thank a lot for your answer. Maybe my mistake this. After this I do not use 60V input. I hope I do not show this error again.

I placed my opamp in cooler with screw. In picture 1 Its shown. In pıcture 1 is not opa549 but normaly I insert like this. Also I send my Opamp picture(picture 2).

Thanks.

Picture 1

Picture 2

Hi Thomas,

I remember somethink. After one opamp was demage. I change this opamp and I supply my system -+15V and I use 3 day. After I show same error different opamp. Maybe error is different.

Thanks

Hello Yakup,

Thank you for the information you have provided. Can you describe how you are controlling how much force is being used when fastening the TO-220 tab screw and nut to the heat sink? I am still concerned that if too much force is used the OPA549 die inside the package may be getting damaged.

Thank you, Thomas

Precision Amplifiers Applications Engineering

Hi Thomas,

I place the TO220 tab surface exactly parallel to the heatsink and tighten the screw at the maximum rate. 

Thanks.

Hi Thomas,

Thanks your answer. Our cooling system(aluminum)  has  heat sink style cooling fins on the bottom of the sheet and also we use fan to reduce aluminum temperature. I will try my system again paying attention your advice. After I write result in here.

Thanks.

Hi Yakup,

We haven't heard from you in a while, we hope your issue is resolved. I am going to close this thread now. Feel free to reply to to re-open if you have any questions moving forward.

-Tamara