Astable at 10Mhz

[soundman]

Hello guys,
I want to use a 4047 as an Astable at say 10Mhz, but have no idea If the chip is able to support that frequency or not? Sorry the datasheet was not help full. My chips are labeled as CD4047BE & HCF4047BE
Thanks for any help.

 

[ericgibbs]

hi,
All the data I have for the 4047B shows a limit on the graphs of 10^6 cps ie: 1mHz.

EDIT:
Also the pulse transition times in the order of 50 to 100nS, which suggest that 10mHz is not possible.

 

[soundman]

Thanks, So it is impossible to reach that freq with the said chip.
I have seen a circuit used 555 IC as an Astable mode. It had a 1PF ceramic connected to pin2 and ground, It used a 82k resistor for pin6 and pin2&6, the resistor which was connected to pin7 and the positive rail was a 6.8k, I guess those values give a freq of almost 8Mhz, right? If so , is a 555 reaches to that high frequencies at all?

thNKS

 

[ericgibbs]

Thanks, So it is impossible to reach that freq with the said chip.
I have seen a circuit used 555 IC as an Astable mode. It had a 1PF ceramic connected to pin2 and ground, It used a 82k resistor for pin6 and pin2&6, the resistor which was connected to pin7 and the positive rail was a 6.8k, I guess those values give a freq of almost 8Mhz, right? If so , is a 555 reaches to that high frequencies at all?

thNKS

According to the 555 data, it will work up to 1mHz but its not recommended for over 500kHz.

 

[soundman]

So it would be a trouble for me to find a chip to generate a square or ramp wave at 10Mhz, right?

 

[ericgibbs]

So it would be a trouble for me to find a chip to generate a square or ramp wave at 10Mhz, right?

hi,
If you just want a 10mHz square wave at TTL levels, buy a 10mHz osc module, 4 pin package +5V 0V Out and Enable pins.

 

[Ubergeek63]

why not just use a 74HC14? they will run 25MHz as a relaxation osc.

 

[audioguru]

High speed Cmos (74HCxxxx) works up to about 30MHz. But nobody makes a 74HC4047. Use another type of high speed Cmos oscillator.

 

[soundman]

High speed Cmos (74HCxxxx) works up to about 30MHz. But nobody makes a 74HC4047. Use another type of high speed Cmos oscillator.

Thanks for all inputs,

Do you know any?

The power supply is 12V so I think I will have sort of problem using 74HCxxxx chips, right?

What do you mean by "Use another type of high speed Cmos oscillator"?

 

[Ubergeek63]

High speed Cmos (74HCxxxx) works up to about 30MHz. But nobody makes a 74HC4047. Use another type of high speed Cmos oscillator.

i said to use a simple schmidt... not a 4047

 

[Ubergeek63]

Thanks for all inputs,

Do you know any?

The power supply is 12V so I think I will have sort of problem using 74HCxxxx chips, right?

What do you mean by "Use another type of high speed Cmos oscillator"?

that is not a problem... that is what regulators are for... to many people use 4xxxx parts to try and short cut designs

you have to ask yourself what you NEED and WHY. 12V is really weird for a 10MHz system. the only thing i can think of of hand is some screwy, ill advised, jury rigged PWM that needs the counter running that fast to drive a FET gate.

if something like that is the case run the logic at 3V and use a FET driver, that is what they are for.