Does anyone know the expected voltage drop for the protection diode on OPA2227 (OPA227 dual pack) op-amps?
We are trying to perform static MDA testing between pins 2 to 3 and 5 to 6 (for our production process) and are experiencing a wide range of readings from 0.75V to open circuit.
Packages with high voltage drops (>0.8V) appear to be experiencing noise issues in a basic test circuit.
Thanks
Viv
Viv,
There are two sets of back-to-back diodes protecting the inputs from excessive differential voltage between the input terminals (see the schematic below). For that reason, forcing ANY current between pin 2 and 3 or 5 and 6 will cause (depending on current polarity) two and NOT a single diode, DBB1 & DBB2 or DBB3 & DBB4, to turn-on at any given time so the expected voltage drop should be between 1.2V to 1.4V at room temperature and change around -4mV/deg C. This would probably explain the large variation in your voltage drop measurements. However, keep also in mind that back-to-back diodes will turn-on only if the input common-mode voltage is within the supply rails and one of the ESD diodes, D1 through D6, will turn-on when any of the input/output pins is taken above VDD or below VSS supply. In either case, it is necessary to limit the current to less than 20mA to prevent a permanent damage to the IC.
