74HC4060 max oscillator frequency - Page 1
Forum section: electronics / projects

author: reindeerer
author_rank: Newbie
timestamp: August 12, 2017, 05:37:05 am
content: Hi, I'm puzzled over this. I'm trying to figure out how much frequency i can expect to reliably squeeze out of this at say, 3.3V. Datasheet gives fMax at 4.5V Min=30 and Typical=80Mhz. That's a very wide range.. if i put these in a design, should i expect the frequency with fixed RC circuit to be just randomly somewhere in between, depending on individual chip ?These table values refer to either 50pF or 15pF Cl in circuit, but Cl typical value is given as 3.5pF and then formula recommends it to be over 50. I'm lost on how small can it realistically be ?

author: Rerouter
author_rank: Super Contributor
timestamp: August 12, 2017, 06:11:04 am
content: Note. the max frequency is referring to the maximum frequency it will reliably count on. this varies chip to chip, so the typical and minimum are only what they guarantee, it may work much higher, but they wont guarantee if you buy 2 batches it will be the same.for 3.3V i would expect a range of 20-45Mhz, but you would need to refer to all the propegation delays and such to get the actual number.As for what frequency you expect, ideally that should be dominated by your RC setting the timing. if you want it to work every time, you would design for the minimum.

author: reindeerer
author_rank: Newbie
timestamp: August 12, 2017, 06:48:08 am
content: Thanks for quick reply, that's what i was kind of expecting but didn't want to hear. Doesn't seem like 4060 would be available in any faster CMOS variant either, only HC and LV and both have similar speed.

author: Rerouter
author_rank: Super Contributor
timestamp: August 12, 2017, 07:15:44 am
content: Well it comes down to what your hoping to accomplish, i am quite curious why you are choosing a ripple counter instead of a synchronous. e.g. 74XX690.If you still want ripple counters, here is one with a better typical spec,https://www.digikey.com.au/product-detail/en/toshiba-semiconductor-and-storage/74VHC4040FT(BJ)/74VHC4040FT(BJ)CT-ND/5155785At the far high end there is this guy for a syncronous (ECL logic though)https://www.digikey.com.au/product-detail/en/on-semiconductor/MC100EP016AFAG/MC100EP016AFAGOS-ND/920658

author: Zero999
author_rank: Super Contributor
timestamp: August 12, 2017, 08:31:12 am
content: Quote from: reindeerer on August 12, 2017, 05:37:05 am3.5pF sounds like the parasitic capacitance of the gate input and package to me. The parasitic resistance of the output will be on the order of 50R, for a 74HC device. As long a R & C are significantly greater than the parasitics, then it should work and give a predictable frequency.Quote from: Rerouter on August 12, 2017, 07:15:44 amWell the nice thing with the '4060 is it has both an oscillator and counter in the same package, making it very cost effective.

author: Circlotron
author_rank: Super Contributor
timestamp: August 12, 2017, 12:33:23 pm
content: I tricked myself badly a long time ago with a CD4040 counter. Had it counting away at much higher than what the datasheet said it could until I finally realised that above a certain frequency the first counter stage was only triggering on every second input pulse. I thought that if the clock rate was too high it would just stop counting.

author: David Hess
author_rank: Super Contributor
timestamp: August 12, 2017, 07:06:58 pm
content: Quote from: Rerouter on August 12, 2017, 06:11:04 amDifferent datasheets at listing the same thing in two different ways.Texas Instruments lists the *maximum* frequency at 4.5 volts over the commercial temperature range as being 25 MHz meaning that they guarantee that it will operate at that frequency. NXP lists the exact same specification as 24 MHz *minimum* but they mean the same thing.

author: reindeerer
author_rank: Newbie
timestamp: August 12, 2017, 08:39:49 pm
content: Quote from: Rerouter on August 12, 2017, 07:15:44 amVHC4040 looks like a good option, Fairchild makes it as well. I'll have to keep the oscillator separate, can't get single chip as i was hoping. As to why ripple, i basically just need a frequency divider from 80-100Mhz range down to ~kHz level to be counted by an MCU.

author: bd139
author_rank: Super Contributor
timestamp: August 12, 2017, 09:42:32 pm
content: What about a 74F74? Good to 125MHz. 100MHz in, 25MHz out which is surely slow enough for an MCU to handle (PIC anyway - I can get 30MHz counting out of them easy)