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activated, the power stage is disabled automatically (no matter what control or firmware does), and
the motor shaft will slow down until it stops under its own inertia and frictional forces.
The CBC-EIP STO works with negative logic, deactivating the power stage by default. In order to
activate the power stage, and therefore allow the motor operation, two differential inputs must
energize. These inputs activate two optocouplers that enable the CBC-EIP power stage operation. On
the contrary, if the STO inputs are not energized, the transistors of the power stage are turned
off and a STO fault is notified. During this state, no torque will be applied to the motor no matter
configuration, or state of a command source. This input should not be confused with a digital input
configured as enable input, because enable input is firmware controlled and does not guarantee
intrinsic safety as it can be reconfigured by a user.
The following diagram shows a schematic of the STO circuit.
Figure 9. Schematics of STO circuit.
The CBC-EIP STO has been designed to be compliant with Safety Integrity Level 3 (SIL 3) according to
IEC 61800-5-2. In order to fulfil the requirements, the STO reliability has been increased by means of
the following characteristics:
• Two fully independent STO channels
• STO Feedback output for external diagnostics
• Detection of abnormal STO operation
2.1.4 Fully independent STO channels
The power stage logic is supplied by two cascaded MOSFET transistors. Each transistor is activated by
an independent isolated STO input. The design guarantees that a single failure will not accidentally
activate the power stage.
STO firmware notification:
An STO stop is notified to the control DSP and creates a fault that can be read externally, however its
performance is totally independent from control or firmware. When the STO is not connected it is
virtually impossible to apply power to the drive.
2.1.5 STO Feedback output
By changing a resistor, the isolated output GPO4 can be configured as STO Feedback (STO_FB). The
STO_FB output is normally active, providing a closed contact. When one of the STO inputs becomes
de-energized (low-level), the STO_FB becomes low-state too.
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