Mehmet Fide

LC60: ESD over 30kV

Discussion created by Mehmet Fide on Feb 26, 2008
Latest reply on Feb 27, 2008 by Celso Monteiro
Hi,
 
We are producing solid state energy meter and many people try to tamper with them.
Their last toy is oven lighter or high voltage lighters that can be found easily in the area.
 
Their effects at meters are similar to ESD test in the standard, but they have so much voltage than the standard's.
 
Here is some effects of a 30kV lighter at our meter that we use LC60 in:
- External 32.768kHz low power oscillator lost, and DCO lose of lock. After the effect, it locks again.
- Some LCD registers such as FPENR0..4 are changing.
- Some zeropage registers are changing.
- If I enabled PIN reset functionality, MCU resets yourself. If I disabled pin reset, no reset occurs.
- Some times with a single pulse, the MCU enters in unknown state, and it stops responding, codes stop flowing. Even if I use COP with internal 1Khz source, I doesn't reset the MCU. I have a lot of trap in the code to detect unknown state and reset it to modify MCU, but all of them didn't work. Only way to exit unknown state, it need second ESD pulse. :smileyindifferent:
- Some time, Our measurement unit starts consuming so much current about 100mA (normaly 15mA). To modify, it need power on reset or second ESD pulse.
 
I'm waiting for your advice to improve ESD immunity of our meter.
Regards,
BP.

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