Hi Guys,
A little more on the project.
The worst case scenario when receiving a new board is this: You hook up the programmer/debugger and power the board and nothing happens. The board just sits there looking at you looking at it. So, I just couldn't resist powering the board and attempting a program download so I would know whether or not I had a good starting point for porting the software from the breadboard to the prototype.
Success!!
The CPU and Engine Control IC are very low power devices which makes the power supply design easy.
The front end of the power supply consists of a high voltage schottky diode for reverse voltage protection, a 24 V transient voltage suppressor, and a small inductor to filter high frequency noise.
The front end feeds four linear regulators. One to power the analog circuitry, one to power the MAP sensor, one to power the CAN bus, and one to serve as the pre-regulator for the MPU power regulator. The large number of regulators is all about fault tolerance.
These regulators are pretty trick.
Wide Input Voltage Range: 4.5V to 55V- Up to 70V transient- Under Voltage Lock Out (UVLO): 2.7V typical
Extended Operating Temperature Range: -40°C to +150°C
Low Dropout
Rated for continuous short to ground (MAP Power Fault)
Anyway, the power supervisor monitors the output of MPU pre-regulator. When the output of the pre-regulator drops to approx 4.7 volts the MPU is reset. So, the 3.3 V MPU regulator never drops out of regulation before the MPU resets. The MPU will never see an unstable voltage.
I did a quick check of the reset voltage. It was somewhere below 5.5 Volts. I wanted it to be below 6 volts so I'm happy with that.
I'll go away for a while now for the rather lengthy process of porting the software.
Thanks for listening to me ramble.
Wes