CD4060 frequency/ocialiation configuration

[bitman]

I know it's an old chip - but I am struggling with how to set R1, R2 and C to get a needed frequency. I understand I can use a crystal, but for now I'm trying to understand the values. From my own experimentation there are some limits that aren't clear to me - so I wondered if there isn't better (for dummies kind) materials explaining the relationship between the R and C values. I don't get a traditional RC formulator to work, mostly because there are two resistors and well, I find lots of different setups out there that aren't matching the datasheets including pulling the  C to ground through a diode ... anyway ..

Question: What formular should I use to calculate R/C for a given frequency? Let's say I want the pulse on pin 11 to be 1Mhz - how do I determine the C and R values?  Reading the very old fax/photo copy TI uses, I see the following (which is hard for me to grasp):

Rs is 2Rx to 10Rx
T = 2.2 RxCx

Which R is this talking about? Rs barely seem to have an effect on the frequency - Rx seems to cut out the frequency when I get close to 200Khz on Q4. I'm using a 10pF cap and using less than 2.2kOhm as Rx just makes the oscillation stop.  I've tried 5v and 10v input - this is definitely a circuit that gets more stable at higher voltages, but 5v is what I'm trying to make it work at.

The datasheet also have two different max values for frequency on the input (one says max 3.5 Mhz, the other says "3.5Mhz->7Mhz). Since this is ancient documentation/chipset I'm obviously not reading it right, so I'm hoping for some guidance on how to read this so I can set things to the proper values.

Thanks.

[Zero999]

The maximum frequency depends on the power supply voltage, temperature and varies from IC to IC.

Low values of C and R will give unpredictable results,  as the parasitic capacitance and output resistance of the gate will start to dominate. To get frequencies above a few hundred kHz, you need to use an LC oscillator, crystal or ceramic resonator. It even implies this on the data sheet. "RC oscillator frequency of 690kHz min.  at 15V" At 5V the maximum RC oscillator frequency will be lower.
http://www.ti.com/lit/ds/symlink/cd4060b-mil.pdf

Here's a tutorial on LC oscillators with CMOS gates.
https://wiki.analog.com/university/courses/alm1k/alm-lab-21

[danadak]

How accurate do you want the frequency to be ?

The period for 1 Mhz , T = 1 / F = 1 uS.

So 1 x 10^-6 = Rx x Cx

That being said max F is 810 Khz at Vdd 10V, even lower for 5V.


https://www.electronicspoint.com/threads/74hc-oscillator-how-fast.282578/


Hero999's recommendations to use LC or crystal make much more sense. And consider
using a 74HC4060 vs the CD4060.



Regards, Dana.