• Resolved

OPA548: Connecting the Thermal Shutdown Status output pin of several OPA548 devices together.

Part Number: OPA548


I need to monitor the thermal shutdown pin of four OPA548 devices.

Do you see any problem with connecting the shutdown pins of four OPA548 devices together at the input of the MOSFET in the circuit shown on figure 29, page 17 of the data sheet ?


  • Hello Aramis,

    The OPA548 thermal shutdown function of the E/S pin is an output voltage function. The pin has the normal state where the output level is typically at (V-) + 3.5 V, and the thermal shutdown state where the output level is (V-) + 0.8 V. It has fairly high output impedance and can only source about 20 uA and sink 5 uA, respectively.

    If you connect the E/S pins of two or more OPA548 together and attempt to utilize the thermal flag function, it is equivalent of connecting different voltage sources together. They may be in the same state, but if one needs to be in the other state they will be in conflict. Where exactly the E/S pin level goes will depend on how the sinking and sourcing of current goes between the various OPA548 devices.

    A better approach is to keep the E/S pins being used in the thermal flag mode isolated from each other. Simply use an OR or NOR function for the E/S pins. See Figure 31 in the OPA548 datasheet and the way an 74HCT04 inverter is connected to drive an LED as an indicator of normal operation/ thermal shutdown. But instead of using the inverter use the OR/NOR 74HCTxx to indicate when any one of the OPA548 amplifiers is in thermal shutdown.

    Regards, Thomas
    Precision Amplifiers Applications Engineering