OPA2228: OPAMP failure

Hello Venkata, 

You will likely need to provide the exact schematic (source and load Z, etc) and probably some photos of failed units showing markings top and bottom. 

Hi Venkata,

and how do you generate the supply voltages of OPA2228?

Kai

Hai ,

I am attaching the schematic for your reference.

IC Batch is :71Z24TW

Power supply voltage we are deriving from 110V DC by using a Top switch + transformer + feedback regulator(TL431) (both +/-18V) which is a standard stepdown converter in our projects. Max tolerance is +/- 0.3V.

Venkat

What is the load for the 2nd stage?

Hai,

Second stage is with OPA548 opamp, Load is transformer + resistive load - resistance of 13ohms.  

Uh-oh! Transformers are especially critical loads because they can generate destroying inductive kick-backs :-(

In any case, you should add protection diodes (free wheeling diodes) to the output of OPA548 as shown in figure 38 of datasheet of OPA548.

Kai

And you should connect TVS from the supply voltages to signal ground to prevent the inductive kick-back from making violate the maximum supply voltage of OPA2228.

Kai

Hello Venkat,

The OPA2228 has a long and excellent reliability history so it is unusual for customers to have reliability problems providing the +/-18 V supplies are not being exceeded. 

It is risky running the OPA2228 supplies at the absolute maximum level because even though it has some supply margin it is plausible that during supply turn-on/turn-off that is being momentarily exceeded. It is best to equip the OPA2228 supply pins with a DSO having 10x probes and observe the pins during turn-on and turn-off to make sure you are not exceeding +/-18 V. Additionally, although I expect your OPA2228 circuit is stable, do observe the output to make sure that there isn't a high frequency oscillation present. Unexpected oscillation can lead to high current that could potentially damage a device.

Please be sure that the OPA2228 you are using was obtained from TI directly, or from one our TI authorized distributors. If they weren't obtained from TI reputable sources you have to be careful of gray market devices that don't meet the OPA2228 supply specifications.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hai Thomas,

I have verified the Supply voltages at power On/Off and found the supply voltage is reaching +/-18V with soft start. No spikes or overshoots on supply voltage. But the voltage is exceeding +/- 18V by maximum of 0.2V. Will this create any issue or is there some margin inside the IC. 

Also I have verified for any transients occurring during the OPA548 transformer load connect and disconnect. But there is no change in supply voltage.

How to verify the IC whether it is genuine or not?  Can we get any info from TOP marking or failed ICs.

Regards, Venkat

Hi Venkata,

limits are limits !

Just reduce the supply voltage of OPA2228 in order to you never exceed the absolute maximum ratings and you will be fine :-)

Kai

Hello Venkat,

As Kai said "limits are limits." It is never a good practice to operate a semiconductor at its absolute maximum rating and exceed it - even by a small amount. If you can back off on the OPA2228 supply voltage by a half-volt or more each and still meet the output swing requirement, then likely the problem can be resolved providing they are genuine TI OPA2228 op amps.

The TI product verification procedure is to contact the TI distributor from whom you purchased the OPA2228 product, and explain that you need product verification. The distributor won't be able to tell you directly about the material, but they can work the issue back through TI. TI maintains complete records on date/ lot codes, and marking formats for each product and package type. TI can determine from the marking information if the product is valid TI, or not.

Regards, Thomas

Precision Amplifiers Applications Engineering