ULN regulator with more current capability than LT3042?
The details are on the LT3042 datasheet.
A small series ballast resistor is used in series with each output and the Iref terminals are connected in parallel so only the offset of the unity gain output buffer is of significance.
Bruce
On 20 March 2018 at 02:23 Peter Vince <petervince1952@gmail.com> wrote:
Please forgive this naive question, but I am concerned about the idea of
simply running two regulators in parallel. Just like you don't put two
batteries in parallel, how do you ensure accurate load balancing between
the two? I would worry that one of them, with a fractionally higher
voltage, would be driven into saturation, thus ruining any noise
isolation. I must be missing something here?
Peter
On 18 March 2018 at 22:43, Charles Steinmetz <csteinmetz@yandex.com> wrote:
Tom wrote:
Run two in parallel for twice the current and less noise?
This is actually a better solution than using an LT3045, for two reasons.
First, as Tom noted, by paralleling two devices, the noise is reduced by
sqrt 2 = ~1.4:
"Designed as a precision current reference followed by a high performance
voltage buffer, the LT3042 is easily paralleled to increase output current,
spread heat on the PCB and further reduce noise -- output noise decreases
by the square-root of the number of devices in parallel." [LT Journal of
Analog Innovation, v25 n1 Apr 2015]. <http://www.linear.com/docs/46398>
Second, it reduces the dissipation of each regulator, so they run cooler.
And as LT says, it allows spreading the heat on the board (but it is not
advisable to put them too far apart).
The primary disadvantage is that two 3042s cost about half again more than
one 3045. Also, board space may be a factor in some applications.
So, unless you are extremely tight on board space or the ~1.5x cost
increase is prohibitive, two 3042s in parallel are a better solution than
one 3045 if you are seeking the lowest noise possible.
Best regards,
Charles
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Hoi Gerhard,
On Sun, 18 Mar 2018 21:41:28 +0100
Gerhard Hoffmann dk4xp@arcor.de wrote:
Use the LT3042 with an external power transistor, such as D44VH10G:
<
https://www.flickr.com/photos/137684711@N07/29197476530/in/album-72157662535945536/
Performance is about the same as the LT3042 alone. That is exactly the
circuit from the data sheet
Have you measured it's dynamic performance?
I did some spice simulations some time ago and noticed that there are
some load conditions where this circuit is very close to oscillation
(ie load changes lead to heavy ringing)....of course, this is under
the assumption that the spice model of the LT3042 is accurate in that
regard.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
Am 20.03.2018 um 10:09 schrieb Attila Kinali:
Hoi Gerhard,
On Sun, 18 Mar 2018 21:41:28 +0100
Gerhard Hoffmann dk4xp@arcor.de wrote:
Use the LT3042 with an external power transistor, such as D44VH10G:
<
https://www.flickr.com/photos/137684711@N07/29197476530/in/album-72157662535945536/
Performance is about the same as the LT3042 alone. That is exactly the
circuit from the data sheet
Have you measured it's dynamic performance?
I did some spice simulations some time ago and noticed that there are
some load conditions where this circuit is very close to oscillation
(ie load changes lead to heavy ringing)....of course, this is under
the assumption that the spice model of the LT3042 is accurate in that
regard.
No, I didn't. My oscillators are quite boring loads for a regulator.
regards, Gerhard
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of John
Ackermann N8UR
Reviving the conversation about superb voltage regulators, I am looking
for one to run the analog and PLL bits of a high performance frequency
synthesizer chip.
The current drain looks to be about 160-180 mA at 1.8 V, which is
uncomfortably close to the limit for the LT3042 (200 mA). The
manufacturer's evaluation board uses a MAX8869, which appears to be
nowhere in the LT3042's league, but will source 1 A.
Any recommendations for a 1.8 V regulator a little beefier than the
LT3042, but with similar noise performance?
These days, the best RF synthesizer and clock generator chips include dedicated low-noise LDOs inside the package. It's rarely worthwhile to use a quieter regulator than the manufacturer recommends, or one that's quieter than whatever is on their own demo board.
One very nifty example is the LMK61E2, which I X-rayed a while back:
http://www.ke5fx.com/LMK61E2_30kVp_20s.png
The overall package is only about 1 cm square. The synthesizer has its own die, while the input regulators and (presumably) their bypass caps are mounted directly above the Vdd input pad. According to TI, the PSRR of the internal LDO that runs the analog section is better than 70 dB at offsets below 1 MHz. So you could even power it directly from a switcher, assuming you keep a leash on its harmonics.
-- john, KE5FX
Miles Design LLC
Before adding complexity of parallel devices or external passing, why
not just try the old parallel-resistor trick? If the load takes a
certain minimum current under all conditions, provide less than that via
a resistor from the raw source to the regulated output, likewise under
all conditions. The main regulator will still do its thing, but not have
to supply all the current. You're just looking to get a little more
margin between the spec current and actual load. The short-circuit
current would be increased too, so take that into account.
Now some will say, "what about the ripple voltage from the raw supply
causing ripple current going right to the output?" Depending on the
regulator's characteristics, I think it should be able to handle it just
fine - it's easy enough to hook it up and see how it works.
It would be good have OVP on the output regardless of the regulation
scheme to protect the load if it's sensitive to OV. Obviously, the
parallel resistor one could allow the voltage to go high if some load is
lost, but the same can happen with a regulator failure too.
Ed