electrostatic discharge - mc9s12dg256

[support_semitro]

I use the mc9s12dg256 controller. I apply 8KV air discharge and controller resets. Schematic and pcb have been made according to freescale reference.

Does anyone know what is going wrong?

thanks

NIKOS

Added p/n to subject.

Message Edited by NLFSJ on 2009-05-27 07:02 AM

[astro_goto]

Electrical discharges in the vicinity of any microprocessor is bad news. Any wires attached to the micro, whether to the ports or as power supply leads, can act as antennas conducting induced voltages to the cpu. Minimizing wire lengths will help. Thorough shielding sometimes will help. If you still experience problems try connecting schottky diodes from each such lead to +5v and to ground.

I used to design microprocessor controls for ion implanters and x-ray steppers which operated in the vicinity of high voltage discharges. The micros had to be heavily shielded and connected to the outside through fiber optic cables. No direct connections.

Design the software expecting COP to restart the cpu when needed.

If all your efforts fail, consider contacting a consultant from the ion implanter industry. These problems have been solved before.

Regards,

Astro_goto

[Lundin]

What is "Freescale reference"? Are sensitive pins connected to pull resistors? The reset pin, the IRQ pins, the PE7 pin, the BKGD pin etc.

Is it possible for you to upload the schematics to this site?

[support_semitro]

Hi

I attach the schematic, pcb and the sfr configuration.

thank you

NIKOS

[Lundin]

On the "old" HCS12 D family, you need a low voltage supervisor circuit on the reset pin, they don't have it internally.

100nF may be too big for the reset pin. The mcu expects a rather steep reset, and I know that you can get problems if that cap is too large. I'd recommend something around 100pF.

Apart from that, the design looks ok as far as I can tell.

[AndersJ]

Try a common mode choke on the power supply input.

Anders J