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OPA548: Thermal shutdown issue

Sai Kiran Sharaf
Prodigy 65 points
Part Number: OPA548

Hi,

       1) I am using OPA548 as power amplifier for driving the DC motor with proper Heat Sink.The IC is going into thermal shutdown mode after running the motor continuously for 4 minutes.I measured the temperature at which thermal shutdown has occurred and it is 101 degC. But in datasheet it is mentioned that thermal shutdown occurs at 160 degC.

2) My motor is drawing only 300mA at 28V but, the IC is dissipating lot of heat,how to address this issue? 

3) Is this IC is suitable for driving the motor continuously for 20 minutes at working temperature of +75 degC 

  • 0
    TI__Guru* 93105 points

    Hi Sai,

    The OPA548 thermal shutdown occurs when the junction temperature (Tj) of the output transistors reaches approximately 160°C. The temperature measurment you are making is an external measurment somewhere on the TO-220 package (Tc) , or the heatsink (THA). Output transistor Tj  will always be the hottest point in the OPA548 and surrounding circuit. The 101C you are measuring externally coincides with a Tj of about 160°C and that is why shutdown is taking place. It isn't until the Tj drops below 140°C that the output turns back on.

    The OPA548, its mounting and connection to the heatsink, the heatsink thermal properties, and air flow around the heatsink all have their individual thermal characteristics that must be carefully considered to maximize heat removal. Section 11 in the OPA548 datasheet provides a complete disscussion about the thermal considerations that must be observed to attain good thermal performance.

    To determine if the motor can be driven continuously with a TA of 75°C, we would need to know what output voltage (ac, dc) is being supplied to the motor, if the 300 mA current peak or RMS, and the thermal resistance of the heatsink. Actually, the information in section 11 should be sufficient to determine if this is doable once the unknowns are established and applied.

    Regards, Thomas

    Precision Amplifiers Applications Engineering