# Oscillator

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#### boy

##### New Member
Hi.. I'm new here. I want to ask about crystal oscillator. I'm making an oscillator using an IC (MM5369), a 17 stage oscillator / divider. At the IC datasheet, the crystal that I should use is 3.579545 Mhz to result a 60 Hz output frequency. But I need only 50 Hz. I'm looking for how to calculate the crystal that I have to use, so the output will be 50 Hz, but all I found is how to calculate the capacitor load at the maximum load so the frequency output of the crystal will at a stable condition.

Can anyone help me how to calculate the crystal that I should to use so the frequency output from the IC MM5369 will be 50 Hz? I want to put down the circuit design from my oscillator, but it's look like I can't put it. If anyone need the circuit design to found out the formulas, please send me an e-mail to [email protected], I'll send the design to you.

Regards

#### Roff

##### Well-Known Member
The MM5369 apparently divides by 59659, so you will need a crystal frequency of (50*59659)=2.982950 MHz. This might be difficult to find, since I don't think it is commonly used, and a one-off custom would be expensive.
A 1 MHz oscillator with divide-by-20000 would seem to be much simpler, but it still requires several ICs. There may be ICs available to solve this problem that I know nothing about.

#### pebe

##### Member
Yes, change the xtal frequency in proportion to the change in freq you want. 3.579545MHz x 50/60 = 2.982954167MHz (or as close to that as you can get).

#### Sebi

##### Active Member
I agree with Ron: the solution is the 1MHz Xtal divided with four decade counter and a flip-flop. The result is an symmetrical 50Hz. All components available. The MM5369 designed for 60Hz country.(for 50Hz country also existiert a time-base IC-s e.g. SAJ300T, but i think today also discontinued. This is a very good chip, it have ppm pins for precise 50Hz tuning...)

#### boy

##### New Member
OK, there are two ways to calculate the frequency:
1. I must divides with 59659
2. I can use the other one that pebe said

From #1:
If I want to divides with 59659, from where this number come from? Is it listed at the datasheet? If it is, can you give me the URL for the datasheet, because the datasheet that I have doesn't contain that thing.

From #2:
If I want to take the other one that using a formula, from pebe (50/60)*3.579545MHz, my question is :
1. Is fxtal ~ foutput?
Because if I write down the equation, from your calculation, it will be:
(fxtal1/fxtal2)=(foutput1/foutput2), so the fxtal ~ foutput
2. If the equation from the above is right, which formulas from oscillator
equation that contain those part that you use? And are they just a
regular formulas that I can find in the literature books?

Regards

#### Roff

##### Well-Known Member
The number 59659 is simply the ratio 3579545/60. You put 3579545 in, you get 60 out. That number is actually shown in Fig.6 of the datasheet.

If you multiply 59659*60, you will see that the oscillator frequency would actually have to be 3579540 Hz. The oscillator frequency is easily tunable to that value, if such accuracy were required.
I realize that you need 50 Hz. You will have to pay a high price for a 50*59659=2982950 Hz crystal. Use Sebi's suggestion instead. You can use a 1 MHz oscillator and two cascaded 74HC390's followed by half of a 74HC74 configured as a toggle (divide by 2) flip-flop. You can find an oscillator schematic at this location: http://www.ee.washington.edu/eeca/circuits/F_ASCII_Schem.html#ASCIISCHEM_009

Ron

#### pebe

##### Member
Sebi said:
I agree with Ron: the solution is the 1MHz Xtal divided with four decade counter and a flip-flop. The result is an symmetrical 50Hz. All components available. The MM5369 designed for 60Hz country.(for 50Hz country also existiert a time-base IC-s e.g. SAJ300T, but i think today also discontinued. This is a very good chip, it have ppm pins for precise 50Hz tuning...)
I also agree. But I was just answering boy's original question:

Quote "Can anyone help me how to calculate the crystal that I should to use so the frequency output from the IC MM5369 will be 50 Hz?"

#### boy

##### New Member
Okay, thanks for everyone help.

Now I want to ask again, still the same subject but different component.
It's about the capacitor circuit that connected at port 5 and 6 from the IC MM5369. What's the function from those capasitor? Are they have any connection with frequency xtal value? If I change them with bigger or smaller capacitors, both of them, what's the effect for the input and output? And how I decide the best resistor value for the Rf (above Xtal)? Is there any formulas for calculate Rf or it listed at the datasheet?
And where I can find Xtal datasheet?