Input voltage is between 0-V and
24-V nominal with worst case of 3.6-V as logic low and 20.4-V as logic high. No
intermediate voltage is expected.
The logic low (diagnostic pulse)
in the STO signal is assumed either to be less than 1ms or greater than 2ms. No
intermediate values are allowed.
Diagnostic coverage of STO_1 and
STO_2 and STO_FB subsystems
The MCU and the related
diagnostic software is excluded in the analysis and is assumed to be developed
in accordance with functional safety requirements. The MCU is assumed SIL 1
certified and the software implemented accordingly to meet at least SIL 1.
Output signal STO_FB:
The output voltage is assumed to
be between 0-V and 24-V nominal with worst case of 3.6-V as logic low and 20.4-V
as logic high. The external supply voltage to the 24V STO_FB is assumed to be
protected against over-voltage and is required to remain within 24V ±20%
tolerance.
Power supply rails of STO_1 and
STO_2 subsystem
P3V3 supply: Assumed to be
protected against fault, remains within ±20% tolerance (3.9 V maximum, 2.7 V
minimum. If out of spec, it will be shut down to 0V. When a single protected
power supply is used for both STO_1 and STO_2 subsystems, it shall employ two
independent protection circuits (HFT = 1).
24-V supply: The 24V input supply
for the P24V is assumed to be protected against fault and remains within ±20%
tolerance. If out of spec, it will be shut down to 0V.
Isolated gate drive supply
TIDA-00199
It is assumed that the quad
output rails (VCC2 = +15 V, VEE2 = –8 V) decay to 0 V within less than 10 ms,
after the P24V DC input voltage was disconnected.
It is assumed that all faults
with TIDA-00199 are safe and yield to a 0V output voltage for all quad output
rails VCC2 and VEE2.
Temperature
It is assumed the components
operate within the recommended operating temperature range. A temperature sensor
is required to be added and if the ambient temperature is outside the
recommended operating range all safety relevant supplies will be shutdown. This
circuit is not part of this design.