If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I have a simple oscillator using a crystal, and a hex inverter. It is running at 4MHz. I fed its output to a single uccx732x via a 100nf DC blocking capacitor. The output of the 74hc14's buffering inverter dropped to 1vac (2v peak to peak, i guess the capacitor is causing it to swing negative). There is not any real ringing i can see on the scope, it is a fairly low inductance layout, made right on top of a copper clad board, and any connections other than the ground plane where very thin pieces of copper clad, glued to the ground plane.
I am wondering if i just need to amplify the output of the 74hc14 with some BJT's, or maybe a ucc37322 will simply not run at 4MHz? Maybe even all the otherwise unused internal inverters paralleled would be enough to drive the UCC? I expected the UCC to work with the 5v however many ma output, because it will in a 'mini sstc' even when run at a few MHz. I have done that before, at around 2MHz.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
RTFDS! It says the UCC chip's input must be >= 2V for High and <= 1V for Low. And that its [DC] input current magnitude will not exceed 10 uA.
With a similar exercise, you can figure the drive capability of your crystal oscillator (high and low levels, source and sink output current, rise and fall time). The input capacitance of your UCC driver is probably similar to the standard load capacitance noted in the hex inverter datasheet.
[edit] So the voltage downstream of your coupling capacitor is technically undefined -- it's determined by the UCC input leakage current and its ESD protection diodes. A simple remedy might be to add a pullup resistor or Thevenin pair to set the UCC average input voltage to +1.5 volts. Of course now (if you insist on AC coupling), when the oscillator stops the UCC woudl be midway beween high & low states.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
It turns out there was a problem with the 74HC14. One of the inverters was half dead. It still oscillated fine, but there was no extra inverter to buffer it. Then the IC socket fell apart, and i rebuilt the circuit, and now i am wondering why a 4MHz resonator is resonating at 11MHz...*mumbles something about not using an IC socket this time*
Either way, that anwers the question, thank ya :). Now I'm off, to go pound this hex inverter in the face with a boulder.
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
I think you'll find most gate drivers response to logic-level signals. All of UCCX732X and IXDD414 and TC442X will operate happily with 5V inputs. Short that "DC blocking capacitor" and connect the inverter output directly to the gate driver input!
Arcstarter wrote ...
It turns out there was a problem with the 74HC14. One of the inverters was half dead. It still oscillated fine, but there was no extra inverter to buffer it.
Well diagnosed! I regularly suffered strange CMOS failures from my poor antistatic practices. Whenever you have even an inkling of suspicion about a chip, swap it out for a new one.
It's one of the fastest ways to remove a whole lot of variables from your debugging. If you get the circuit working, you can always swap it back in for proof!
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
As Klugeymatic said, be sure to read the datasheet. All the information you need is in the datasheet including hi and lo thresholds as well as input impedance from the pins, which is either defined in ohms, or as an input current.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
What kind of load does a uccx732x present.
