The OPA2626 looks like a good solution for our need as a high speed 50ohm output driver to a scope/ADC. In our design the output will be connected to BNC connector to the outside world to allow driving a scope or external ADC.
I am trying to protect the OPA2626 output pin from several potential fault conditions:
- For short circuit conditions I am assuming the mid point (aka 2.5V) is the worst case power dissipation in the OPA2626 output stage (I cannot find any data on this in the datasheet) such that the OPA2626 must dissipate 0.12W (2.5V into 50ohms), hence at worst case 172degC/W I should get about 22degC increase from the ambient. If this assumption is correct the short circuit protection should be fine?
- I would also like to protect from reverse voltages applied to the BNC connector by mistake. For this I have added back to back Schottky diode protection. Ideally I would like to ensure these diodes protect the output before the OPA2626 protection diodes do, however I cannot find this information in the datasheet (In fact the Electrical Over-stress section 8.3.2 mentions them but does not indicate when their protection will kick in, presumably similar to the input +/-0.3V)?
- Finally our product may loose power while an output is still driving the OPA2626 output by mistake. In this case the over voltage Schottky diode protection clamping at 5V will be useless as the 5V rail will be off. Can you provide details of the damage voltage on the output pin when the power is not enabled (this is briefly discussed by analog devices engineers here www.analog.com/.../protecting-off-amps.html)
Thanks.