4046 PLL giving constant frequency. Why? Help Plz!

[bee]

4046 PLL not working in Proteus...HELP PLZ!!

Hi,
I am trying to simulate the 4046PLL in Proteus. The moment I short PIN 5 to GND and VCOIN (PIN 9) to GND the VCOOUT (PIN 4) keeps on generating 1kHz irrespective of the values of C1, R1 and R2.

Please help me why is this happening, i.e. changing R1 and R2 should change the freq at the VCO OUT but it is not, WHY???

Circuit is attached below.



Thanks.
Sohaib

 

[juan_zo]

Dear Friend,

I think you need to inject a reference signal in the SIG_IN (pin 14). It is posible, If you do not put this signal in that pin, the PLL compares the RC oscillator frequency vs nothig (0 hz), then, it calculates the difference between, |RC_freq - SIG_IN| = |RC_freq - 0Hz|= RC_freq.
I guess this is the problem.
I hope you can solve it with this piece of advice.

Have a nice day!
Best regards,
Juan_zo

 

[FvM]

A real 4046 can be operated as simple VCO, by using only VCO_IN and VCO_OUT. But the behavioral Proteus model must not necessarily support this operation.

Why are you shorting pin 10, by the way?