I have to admit that I am using X7R capacitors to get them really close to the pins.
(one is 0603 in the middle of the LTZ-pins the other 0805)
But of course film capacitors (e.g. SMD ECHU type) are also possible.
with best regards
Andreas
You can now get 10nF C0G capacitors in an 0603 case. Many are 25V parts, but TDK has a 100V part in that size as well. So, you don't have to suffer the vagaries of X7R, unless you really want the 'voltage squish' and real component losses of X7R. Time marches on, and parts keep getting smaller!
Best Regards
Changing L3 to a resistor would ruin the low output impedance. The trick when makting the OPs output more tolerant to capacitive drive it to have the DC feedback from the output (thus behind L3 or resistor) and the fast feedback via a capacitor directly from the OP. Just the extra cap and L3 instead of the usual resistor could also work reasonable.
Some here may not like the one rather thick line going to the LTZ1000, because of possible thermal gradients. I am not sure it matters.
Build the circuit how you need to, but keep in mind LT/AD does not recommend adding those extra EMI caps, and in our tests normally they are not required, or desired - Especially SMT ceramics always run the risk of adding mechanical noise. The solution is to look at what your EMI source really is, and see if that can't be corrected.
I suggest you might want to test your circuit in your enclosure FIRST to see if they are actually needed at your location, with your test setup. Add the extra caps -only- as required. If your circuit operates normally without them, you're good.
The noise spec you're looking for as defined by LT is if you look at many 10 second periods of your output, you should see an -average- PEAK noise of < 1.2uV averaged across all periods of observation. It is normal to see an occasional peak noise pulse of perhaps over 2uV on occasion, but that is considered perfectly normal and well within bounds.
As Kleinstein noted, normally all traces to the LTZ should have somewhat equal thermal impedance, otherwise you may have created a thermal EMF at the device leads even with the cap over the LTZ. If the thermal EMF is stable you might be OK but the uneven traces might cause problems if any airflow in that area.
I believe the latest guidance for C2 is 22nF. The Linear Tech datasheet calls out the incorrect value for this capacitor on the positive 7V regulator schematic. The capacitor value on the schematic for the negative 7V regulator is correct.
For safety during development, I like to have a 5V zener in series with the collector of Q1 to limit the maximum heater voltage to 10V. This can prevent permanent damage to the LTZ1000A chip if there is a problem during the development process. The Zener is not needed if you use the non A version of the chip.
Good luck!
The last diagram shown an odd connection at the lower end of R10.
The ferrite at the output of the 10 V amplifier would add to DC output resistance. Normally feedback should be all the way from the output - could be down to the connector. In addition some local feedback via a capacitor might help a little with more tolerance to output capacitance. Even if an OP data-sheet says that the OP is stable with 1 nF or maybe 10 nF at the output, this only means it is not oscillating. Added capacitance usually still degrades the output and makes is more prone to ringing / oscillation. For an external output it would be a good idea to have to usual isolation with resistor to have a more capacitive tolerant output.
Those EMF caps Andreas suggested were part of more changes and just adding the caps, but without the other changes will reduce stability and likely make the circuit more sensitive to capacitive load.
Yes, I've built a couple
Insatman, I strongly suggest you look at the Vref circuits in HP (Keysight), et al, Linear Tech
Yes, I've built a coupleIf I would be evil: I would say "glad to be not your customer". But since I'm not, I have never said that.
Of course there is one strategy to ignore EMI. And live like 30 years ago without high speed internet, cable TV, mobiles, WIFI and do not forget to ban the keyless entry FOB for your car. And also prevent your neighbours from using such "devils things" if you are living in a urban region. So today we have the complete frequency range from about 150kHz to 5GHz.
Andreas
...and I was hoping someone would get the "common ground" joke [rimshot]
I'll just show myself out now
If you have any questions about the operation of the LTZ circuit, the best place to go for advice is the engineers at Linear Technology, they will be most happy to answer them, for some reason, that course of action does not seem to be very popular on this forum.
And really - the world is bad enough right now. EEvblog should be about camaraderie and good, fun discussion - please let's just keep it at that level.
If you disagree with me that's fine, but I'll look forward to common ground another day.
I never knew this thread would turn unpleasant, and I can't remember why spending time to post seemed to be a good idea. I have no concern or argument if anyone adds "EMI" caps or not...If it makes you happy, knock yourself out! I just thought it would be helpful to know why you might want to check first to see if it's really required or not before adding extra parts. That was my intention, and maybe that wasn't clear enough.