Sequence of Operations

[electronicsman]

How important is power-up sequence and power-down sequence in Electronic Control Units. Does the sequence mean how do i power on my peripherals and power down the peripherals. Is there more than this? I think i have asked general question. But if you can explain me for any one example ECU, i will try to correlate.

 

[wwfeldman]

audiophiles have long insisted on turning the speakers off (that is, turning the volume all the way down)
before turning the amplifier on or off.
the reason is that you could turn the amplifier on and blast the speakers with an amplifier transient

consider a big machine that moves stuff
if you turn that on before the control system, you have no idea what its going to do
each time you turn it on, without the control system on, it could respond differently

power up and power down includes the peripherals and it includes the control circuits

turn on the processor first so its outputs can settle to OFF
this also allows the inputs to be known when things start up
then turn on the sensor power so the sensors are up and running
then turn on the controlled machines

what is your ECU, and what are you controlling, so you may get a more specific answer?

 

[betwixt]

Power sequencing and potential for failure if not sequenced correctly, depends greatly on the individual design.

From an electrical aspect, the biggest danger is latch-up of interconnections due to being driven when unpowered, it can create a situation where the normal polarity of signals is reversed. If the controller has to initialize a peripheral and it tries before the peripheral is ready to accept instructions it will also cause problems. An unitialized peripheral could pose a danger if for example it controlled mechanical equipment.

The normal method of ensuring correct start-up is to safely apply power in whatever sequence is safe but to hold the control unit in a reset state until everything is ready. Only then is the controller allowed to operate and configure everything before reaching normal running state.

Brian.