OPA549: about Thermal Shutdown

Hi Masazumi,

can you please show a full schematic?

Kai

Masazumi-san,

As Kai has indicated we really need to see a complete schematic for the OPA549 circuit to be able to analyze your results. Additionally, please make sure that we can correlate the scope traces to where they connect in that circuit schematic.

Thank you, Thomas

Precision Amplifiers Applications Engineering

Masazumi-san,

I have been giving your OPA549 thermal shutdown observation more thought. The OPA549 thermal shutdown function relies on a precision bandgap reference and PTAT (proportional to absolute temperature) circuitry. Since thermal sensors are adjacent to the output transistors arrays their thermal shutdown response is fast when the transistor output transistor junctions (Tj) exceed 160 C. The thermal flag provides an accurate indication as to whether the output is shutting down or remaining operating. If the output transistor junctions aren't exceeding 160 C, the OPA549 should remain operating and provide output current.

I do see from the DSO image there is an initial first positive current pulse (pink) that results in a short thermal shutdown flag pulse (yellow). The first positive current pulse, followed by the short thermal shutdown is followed by a negative current pulse (no thermal shutdown after it) and then another positive current pulse and no thermal shutdown.

It may be that the thermal environment is changing through the sequence of events. The two output transistor arrays on the OPA549 do reside in different areas on the die and will have somewhat different thermal paths to conduct and facilitate heat removal. During the positive current pulse one output array is active, and during the negative current pulse the other output array is active. Thermal shutdown should be initiated if the temperature exceeds 160 C in either array. It would be helpful to know how you have set up the thermal path from the OPA549 thermal tab to the water cooled heatsink.

The DSO image clearly shows the current pulse sequence and the short occurrence of the thermal shutdown. If you repeat this sequence does the thermal shutdown occur each time the sequence is repeated?

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Masazumi,

in any case, for highest reliability you should be far away from thermal shutdown under normal operation. But more advice can only be given when seeing the full schematic :-)

Kai

Hello.

My late reply.
Materials such as drawings have been made.
This material is confidential.
Please tell me your email address.

Thank you.