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The objective of the STO_FB is to allow external diagnostics of the STO circuit, allowing an increase of
the system reliability. A common-practice in the diagnostics is to delay the stop of the power stage
from the deactivation of the STO_FB and from the deactivation of the STO inputs. This way, short
pulses can be applied for testing the STO circuit without stopping the system operation.
The following figure shows the timings corresponding to the CBC-I-3/6-C STO:
Figure 10. Timing corresponding to CBC-I-3/6-C STO.
2.1.6 STO abnormal operation
Abnormal operation of the STO is when only one of the channels is energised. In case that only one
channel is energised for more than 1.6 s, a dangerous failure in the system is considered and the STO
is activated in latching mode. The fault cannot be reset until a supply reset is performed.
The following figure shows an example of the STO abnormal operation.
Figure 11. Example timing of the STO abnormal operation.
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