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OPA548 E/S Pin

Peter Justin
Prodigy 10 points
Other Parts Discussed in Thread: OPA548

My OPA448 circuit is functioning correctly with the exception of the E/S pin.  Pulling this pin low, correctly, shuts down the amplifier.  If an excessive load is applied, the device temperature rises and the device shuts itself down - as expected.  However, when the device is in self shutdown it does not take the E/S pin low to indicate shutdown mode.

I need to know when the device is in shutdown mode. The data-sheet clearly states that it is possible to monitor E/S, via a CMOS logic device.  What is going wrong?   All help most welcome.  Thank you.

 

 

 

  • 0
    TI__Guru* 93105 points

    Hi Peter,

    The OPA548 data sheet Applications Information - Thermal Shutdown Status states "The E/S pin can be monitored to determine if shutdown has occurred. During normal operation the voltage on the E/S pin is typically 3.5V above the negative rail. Once shutdown has occurred, this voltage drops to approximately 350mV above the negative rail. Figure 10 gives an example of monitoring shutdown in a single-supply application. Figure 11 provides a circuit for dual supplies." So indeed the E/S pin should be pulling to within 350 mV (800 mV max.) of the negative supply level during thermal shutdown. This level attained is with the E/S pin sinking 5uA.

    If you are using the E/S function too, might there be something about your connection that is forcing the pin to a high level when the OPA548 is going into thermal shutdown? Combinations of the circuits shown in Figures 8 through 13 are needed to use both the E/S function and thermal shutdown flag.

    Regards, Thomas

    PA - Linear Applications Engineering