Crystal problem..

[Shekhar]

Hi all,
I have a RALTRON make 32.768KHz crystal connected to a processor working
on 5V logic. I can measure on a Osc correct freq. But when I connect the
same crystal to a processor working on 3.3V logic, I can see oscillations
at 200mV only on the oscilloscope. I have checked min voltage required for
the crystal which is OK..
CAn someone let me know as to what must be the problem ?

 

[Andrew Holme]

Shekhar wrote:

Hi all,
I have a RALTRON make 32.768KHz crystal connected to a processor
working on 5V logic. I can measure on a Osc correct freq. But when I
connect the same crystal to a processor working on 3.3V logic, I can
see oscillations at 200mV only on the oscilloscope. I have checked
min voltage required for the crystal which is OK..
CAn someone let me know as to what must be the problem ?

Do you have the same loading capacitors in both circuits?

 

[ILYA]

Andrew Holme wrote:

Shekhar wrote:

Hi all,
I have a RALTRON make 32.768KHz crystal connected to a processor
working on 5V logic. I can measure on a Osc correct freq. But when I
connect the same crystal to a processor working on 3.3V logic, I can
see oscillations at 200mV only on the oscilloscope. I have checked
min voltage required for the crystal which is OK..
CAn someone let me know as to what must be the problem ?


Do you have the same loading capacitors in both circuits?

IMHO loading capacitors need for choosing work harmonic of crystal.

check oscilloscope, it must have high input impedance to except damping
of oscillation...

check wires, it must be short to except parasite inductive current...

check startup circuit in chip or external...

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if all work then all ok.