Re: Selection of a USB microcontroller

"Meindert Sprang" <ms@xxxxxxxxxxxxxxxxxxxxxxxxx> schreef in bericht
news:46370f27$0$29000$e4fe514c@xxxxxxxxxxxxxxxxxxxxxxxxxxx
"FD" <fd@xxxxxxxxxx> wrote in message
news:46370182$0$32623$e4fe514c@xxxxxxxxxxxxxxxxxxxxxxxxxxx
I now have 5 designs with ATmega processors to control high voltage DC
and
stepper motors. With about 2000 boards produced, we had several problems
in
the field, like: corruption of Flash (sometimes) and EEPROM (quite often)
and flipping of bits in the fuses (5 occasions). Also brand new chips had
bad fuses, so that they could not be programmed in the circuit (which
could
be fixed by applying an external clock oscillator).

I am inclined to think your board design is not EMC proof.
I have designed a system with an ATmega162 which is tested according to
IEC/EN60945. This also includes several tests where 2kV AC and 1kV DC
transients are applied to all terminals of the device and a 6kV or 8kV
static discharge is applied to the housing or in the very near vincinity
of
the device.

No problems were encountered, the device operated normally or recovered
immediately (watchdog reset) after the test.

Meindert


At first I also thought the design was not EMC proof, but it passed all
tests. We have done additional testing in extreme conditions
(temperature/humidity/power) with large transients on power supply,
terminals, housing and with some sabotage actions like removing shielding
and grounding wires.
Now there are 5 designs which are used in different pieces of equipment.
Weird is that they all show similar problems.

The only thing that I really have found is that the ATmega is very sensitive
about the way it is powered up and down.
A slow rise and fall of power can cause corruption of the EEPROM. I modified
the software to shutdown the application and processor when the power is
removed, but it did not solve the problem completely.

Frank


.

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