OPA549: OP Amp keeps blowing when set up using inverting configuration

Hi Ismail,

The OPA549 should operate in ether an inverting, or non-inverting mode and be reliable if everything is set up correctly in the application circuit. I notice you didn't use any current limiting in the circuit so it is possible for the OPA549 to encounter its maximum current capabilities. Using the current limit provides a level of protection compared to not using it.

I suspect the reason the OPA549 is being damaged likely is related to the speaker load characteristics. If the load is highly inductive the OPA549 may be subjected to inductive kickback EMF. Thee output transistors can experience a load return current condition where the output voltage exceeds the power-supply voltage. The transistors can be damaged in that condition. 

The OPA549 datasheet on Pg. 12 discusses this issue under OUTPUT PROTECTION. Figure 8 shows a Motor Drive Circuit with added output protection diodes used to clamp the EMF event voltage to a safe level. The diodes should be high-current, very fast rectifier diodes. At the time the OPA549 datasheet was written it recommended high-current Schottky diodes and they should work as well.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Ismail,

it cannot be seen how the other terminal of loudspeaker is connected to the rest of the circuitry. Can you post a full schematic showing the entire circuit arround the OPA549.

Kai

Hi Kai,

See image above. Please advise if this is valid and what could be causing the issue.

Thanks.

Hi Thomas,

Thanks for your reply.

I will add the additional snubber circuitry to the design just in case.

Hi Ismail,

Now that we have a bit more information about your OPA549 application schematic I think I see another issue with it. You show that you are driving the circuit with VG1, 20V @ 700 Hz, but what is the actual input voltage range? Is it 0 V to 20 Vpk, or something else? The reason that is important is the OPA549 is not specified as a rail-to-rail input, or output power op amp. It has range limits in terms of the input common-mode voltage (Vcm) and voltage output (Vo) it can support.

I set your circuit up in TINA-TI and performed a dc input sweep where Vi is swept from 0 V to +20 V, which should be within the OPA549 Vcm input range. The various input and output nodes for the two OPA549 amplifiers are measured and plotted to see if any output violations are observed. Here is the test circuit schematic with a +10 V Vi applied, and then the dc sweep results. I used an 8 Ohm resistive load for illustrative purposes.

It is evident from this sweep that the input voltage Vi should not be less than about +3.0 V. If it is the circuit's normal, linear operation collapses. That is because the upper OPA549's output voltage V2 hits the negative Vo output rail. Once an op amp's output hits an output rail it stops operating as a linear amplifier and correct op amp performances can no longer be relied upon, or assured. If this is happening in your circuit with your load that might be another reason the OPA549 is being damaged.

Do further explain exactly what the 20 V, 700 Hz input actually is.

Regards, Thomas

Precision Amplifiers Applications Engineering

OPA549_e2e_090222_01.TSChttps://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/14/OPA549_5F00_e2e_5F00_090222_5F00_01.tdr

Hi Thomas,

My 20V input is coming from an oscillator circuit (wien bridge), it is an op amp powered with 0 - 24V DC on the rails, the output goes from 2.16V - 22.1V @ 700 Hz.