KEA64 does not boot at -10C

[tallxcrunner]

Part number: S9KEAZN64AMLC

Clock: External 8MHz solid state clock that runs a KEA128 and KEA64 at the same time.

ICS: FEE mode to run the bus clock at 16MHz. Problem occurs the same way when I bypass the FLL completely.

LVD: Problem occurs whether or not LVD is enabled.

Problem description:

Given the right set of conditions, my KEA64 will refuse to boot AT ALL. As you deviate from -10C, to say +10C, it will take about 1 second to boot. Then at room temperature, it boots instantly. Again, given the right conditions, which are as follows:

Temperature soak module at -10C while unpowered. You must power the module initially by plugging in a banana jack into the power supply. I have a throw switch that I tested with that seems to bring up the power with a lower slew rate due to bouncing, and this CANNOT cause the issue. It will ONLY happen if you plug the module in with a banana jack, apparently achieving a very high slew rate. (On the 5V bus, banana plug in is 0 - 5V in 20usec, and throw switch is 0 - 5V messily in about 120usec). Keep in mind, I have not officially tested that a fast slew rate is needed to cause the problem. I only have two test cases and that's my best guess as to the contrast between them.

Also, the module must not have been powered in the last 30 seconds, no matter how brief.

I monitor the 5V and reset line while this happens, and both are active almost instantly, with no processor response. I monitor the processor's boot progress with a GPIO pin. Processor expert allows you to put your own code before PE_low_level_init(), which is the very first function in main(). I used it to initialize my GPIO pin (to high), and this happens in the __init_hardware() function. __init_hardware() runs before main(). I still see a low on the GPIO pin until the processor comes up and runs properly, which could be seconds later, or never.

I want to believe that I'm doing something wrong, but it seems silly that something like this can literally vary by temperature. This is REPEATABLE from module to module. It should also be noted that I've never seen this issue occur the same way with the KEA128 that is also on the board.

Any ideas, anyone ever see something like this before?

Thanks,

Dave

[tallxcrunner]

Both processors run off of the same solid state clock, and the kea128 booted correctly every time. I was worried that adding a probe wire to the clock would increase EMI as well, so I was hesitant to try it.

Also, it should be noted that the throw switch signal was significantly more noisy than plugging in the banana jack. The banana jack smoothly rises at a linear rate to 5V, pretty much every time.

That's what tipped me off on the slew rate issue. This is something I will consider for all future designs. I don't think there's any advantage to coming online faster than 200usec.

[markseibert]

Glad you figured out a way to solve your problem. Did you ever look at the crystal startup time in the condition where it was failing? One other question did you check to see that you did not get an inductive spike on the +5V that might cause problems when plugging in the banana jack? 

You may of course just want to move on but in case you are still wondering more about the root cause.3

[tallxcrunner]

It may be a characteristic of this processor that it cannot boot successfully when VDD goes from 0-5V in 20uS. By adding a series resistor to my 5V bus and reducing the power up slew rate to 0-5V in 200uS, it seems to have fixed this issue.