ZHCSNI6 march 2023 OPA928
ADVANCE INFORMATION
The OPA928 uses input protection diodes to limit the input differential voltage range and protect the device against transient currents. The back-to-back, or antiparallel, input protection diodes can be activated by fast transient step responses and cause relatively large amounts of current to flow through the inputs. The inrush current is routed through the antiparallel diodes and to the power supplies to avoid internal damage to the OPA928.
To achieve a femtoampere-level input bias current, the OPA928 uses an internal, high-precision, rail-to-rail guard buffer connected to the noninverting input. The guard buffer drives the voltage at the input of the OPA928 to the guard pins (pins 2 and 7) and sets a 0-V differential voltage across the antiparallel diodes, greatly reducing leakage current though the diodes. The guard buffer is isolated from large capacitive loads at the guard pins by a nominal 1-kΩ resistor. Use the guard pins to guard external components and input traces from possible current leakage paths. For more on guarding, see Section 8.1.2.