4521 oscillator with a 32KHz crystal

[Joer Breton]

Hi everyone,

I need some advices to evaluate which resistors/capacitors values would be
most appropriate for a 32.768KHz oscillator using a 4521 CMOS chip.
The closest example in the datasheet is a 50KHz crystal oscillator. May be
the 18M / 750K / 82pF / 20pF values are ok for a 32KHz crystal but I don't
know for sure. The crystal I got is quite small, very thin cylindrical size
that could fit in a watch, that's all I know about it.

Here is a link to the Motorola MC14521.

http://www.datasheetarchive.com/datasheet.php?article=2251314

I pick this I/C because has built-in dividers.

Joer

 

[John O'Flaherty]

Hi everyone,

I need some advices to evaluate which resistors/capacitors values would be
most appropriate for a 32.768KHz oscillator using a 4521 CMOS chip.
The closest example in the datasheet is a 50KHz crystal oscillator. May be
the 18M / 750K / 82pF / 20pF values are ok for a 32KHz crystal but I don't
know for sure. The crystal I got is quite small, very thin cylindrical size
that could fit in a watch, that's all I know about it.

Here is a link to the Motorola MC14521.

http://www.datasheetarchive.com/datasheet.php?article=2251314

I pick this I/C because has built-in dividers.

The only thing that changes is R0, from 47 kohm at 500 kHz to 750 kohm
at 50 kHz. Try extending that change to 32.768 kHz linearly- giving 777
kohm.

 

[Joer Breton]

The only thing that changes is R0, from 47 kohm at 500 kHz to 750 kohm
at 50 kHz. Try extending that change to 32.768 kHz linearly- giving 777
kohm.

Sounds good.
I just wanted to be sure not to overdrive the crystal but I also not to
underdrive and get unreliable oscillation.

Joer

 

[John O'Flaherty]

Sounds good.
I just wanted to be sure not to overdrive the crystal but I also not to
underdrive and get unreliable oscillation.

Since you're trying new territory, start with the calculated value, and
experiment to see how far you can go to either side without problems,
then leave it around the middle. Maybe a linear middle if it's a narrow
range, or a geometric middle if it's a wide range.