OPA551: Max Voltage Rating for Vout

Hello Hayden,

The OPA551 internal ESD diodes are rated at 10 mA maximum continuous and can't be utilized for surge protection. That kind of protection needs to provided extenal to the OPA551.

The main consideration regarding the output voltage is to prevent the output pin voltage from exceeding the supply rail voltage. This is normally accomplished by connecting fast, or ultra-fast recifier diodes from the output pin back to each supply rail as shown in the diagram below. The diodes must be selected to handle the surge current and also remain off during normal operation. I show the IN4933 fast rectifier, but there are others such as the ES1A and RS1A that could be used.

Then, at each OPA551 supply pin, there needs to be a power supply bypass capacitor that exhibits the least impedance at frequencies associated with the surge event. I show a 100 nF and that may be about right. These capacitors need to be located as close to the device power supply pins as possible and exhibit very low series inductance to ground. The capacitors appear as a momentary low impedance path to ground, to a transient voltage change.

Directly parallel to a bypass capacitor a transient voltage suppressor (TVS) is required. Should an output rectifier diode turn on, the TVS provides a path to ground for the surge current.

The supply line diodes shown in the schematic are actually zeners, but TVS diode should be used instead. The TVS diodes have faster response times then zeners and are designed to handle repetitive current surges. Their standoff voltage needs to be higher than the operating supply voltage. Since you are planning on 12 V supplies, an 18 V TVS should be about right.

Regards, Thomas

Precision Amplifiers Applications Engineering