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OPA2541: output protection tolerance

Part Number: OPA2541
Other Parts Discussed in Thread: OPA2544

In the datasheet on output protection, it says we need to protect the output voltage going beyond supply voltage by using Schottky diode. Is there a tolerance level for the output voltage, for example if I have +11.5V supply rail for opamp, due external condition like lightning in this case, voltage may exceed 11.5V, we are using diode as recommended but it will add some forward voltage drop based on current and will not be exactly 11.5V (as in ckt exapmle below). Considering this is there a + tolerance limit? How it is captured for OPA2541 device datasheet (+2V tolerance) ?

Thank you!

  • Hello Stephanie,

    The Schottky diode serves as a clamp placed across the OPA2541 output transistors intended to protect them in the event of a back EMF generated by an inductive load. If such an event occurs the corresponding Schottky becomes forward biased and clamps the voltage across the affected output transistor to the forward voltage level of the diode.

    A Schottky diode is selected because of its low forward voltage. Practically, its forward voltage is going to be from about 0.2 V to 0.5 V over a wide current range. That is low enough so that the OPA2544 output transistors should be well protected. There really isn't a tolerance requirement because all power Schottky diodes exhibit a low forward voltage characteristic. 

    The OPA2541 datasheet was developed a few decades ago and we now recommend adding a transient voltage suppressor diode (TVS) from each supply lead to ground. These diodes are in addition to the output back EMF protection diodes. They will clamp any excessively high voltage transients coming down the supply line. Below, I show an example of a power op amp having both the output clamp diodes and the TVS diodes.

    The TVS diodes should be selected such that they are off under normal operating conditions, but turn on when a transient voltage a couple of volts above the operating level occurs.

    Regards, Thomas

    Precision Amplifiers Applications Engineering