0
\$\begingroup\$

I need to sequence some micropower (low-microamp range) logic at a once-per-several-minute rate, and am falling back on the good ol' 4060 as my timebase (plus a 138 and a 534 for the sequencing). I need to run the 4060 oscillator in the 1-10 Hz range, which according to the numbers I can do with resistors <100k and X7R chip caps <1 uF or so. Tolerance, drift, board leakage, etc will be adequate for my application based on specs for the passive parts... my question is are there any gotchas running the 4060 oscillator that slow? I know the divider chain is fully static but... rise time limits? Capacitive loading? Other things not mentioned in the datasheet? I get nervous once I get off the edge of the datasheet performance curves...

Thanks!

\$\endgroup\$
  • \$\begingroup\$ Square up the edges, before you get so slow the FlipFlops are operating as linear amplifiers. I'd spend the power to keep 100 nanosecond risetimes (10% to 90%) or faster, into that counter. Depending on the # clock-line buffers/inverters onchip, each of which will speed up the rise/fall times by 5:1 if you input 100nS edges, the important edge region may be only a few millivolts in side. You need to keep the internal ClockUp and ClockDown signals at the same speed, so the FFs don't falsely transfer states. \$\endgroup\$ – analogsystemsrf Feb 7 at 20:54
  • \$\begingroup\$ @analogsystemsrf Maybe you should post your long comment as answer... \$\endgroup\$ – Sparky256 Feb 7 at 21:34
  • \$\begingroup\$ Assuming you're going surface-mount, you could make the oscillator with a 1-gate Schmitt trigger. Or cascade two 4060s and run much faster. \$\endgroup\$ – TimWescott Feb 7 at 23:32
1
\$\begingroup\$

There is no lower frequency limit to the oscillator section of the CD4060. The output of the 2-gate oscillator goes through a Schmitt trigger gate before clocking the first counter stage. I checked several 74HC4060 datasheets, and none of them show the Schmitt symbol. This does not mean that the Schmitt stage is not present; it might have been considered an internal detail. I've never had a problem with either the CD or 74 parts in very low frequency operation, lower than for this thread.

Note: While the chip has no lower freq limit by design, there is a practical limit when the timing capacitor leakage current approaches the magnitude of the charging current.

\$\endgroup\$
  • \$\begingroup\$ " I checked several 74HC4060 datasheets, and none of them show the Schmitt symbol. " - ti.com/lit/ds/symlink/sn74hc4060.pdf \$\endgroup\$ – Bruce Abbott Feb 8 at 4:41
  • \$\begingroup\$ Good to know. I found Motorola, Phillips, and ST that don't. \$\endgroup\$ – AnalogKid Feb 8 at 4:52
0
\$\begingroup\$

Square up the edges, before you get so slow the FlipFlops are operating as linear amplifiers. I'd spend the power to keep 100 nanosecond risetimes (10% to 90%) or faster, into that counter. Depending on the # clock-line buffers/inverters onchip, each of which will speed up the rise/fall times by 5:1 if you input 100nS edges, the important edge region may be only a few millivolts inside. You need to keep the internal ClockUp and ClockDown signals at the same speed, so the FFs don't falsely transfer states.

\$\endgroup\$
0
\$\begingroup\$

Thanks for the comments, everyone.

I did turn up one old Motorola datasheet, of unknown provenance, that seems to suggest (p.5) an operating range of 400Hz < f < 400kHz:

http://dtsheet.com/doc/1031876/motorola-mc74hc4060dt

Who knows how limiting that suggestion was intended to be, since there's zilch about low frequency limits in the formal spec section of that or any other datasheet.

But in an abundance of caution I have switched over to another oldie-but-goodie, the MC14536, running at 437Hz (still draws < 1uA) and set to divide by 2^18... which also pushes me use an HC163 with proper synchronous reset as the sequence counter, cleaning up the overall circuit as well.

I appreciate all the input, and if anyone else with experience running an HC4060 in the 1 Hz range checks into this thread, please by all means let us know your results too.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.