Hi
i am developing a custom power meter board...one of my tests involves switching a 240V-12V halogen lamp ON/OFF. (The lamp uses a plain simple transformer to drop the voltage).
I am sampling the line voltage (suitably reduced) at SD0P0/SD0N0.
I notice the lamp is giving off a lot of noise that presents itself as spikes (of about 5nS) occurring at about 1MHz for about 50uS whenever it switches ON/OFF.
The noise is not affecting the reading that i am getting from the SD24B (i still get the correct voltage).
I placed a scope probe at pin 9 and observe that the spikes have permeated the AVcc line but they dont appear to cause any issues there.
I next placed a scope on the RST pin and noticed that the spikes are also visible there...BUT...in addition, i noticed that the voltage in between the spikes has now trended downwards to about 2V (this trend was not observed at pin 9)....that low voltage now caused the MCU to reset.
So my question:
1. What is the connection between the noise appearing at the SD24 and the decrease in voltage at the RST pin??
2. Why is the MCU internal voltage, as seen by the voltage at the RST pin (in between the spikes), so much lower than AVcc?
Scope captures can be upload if needed.
thanks in advance