Re: [time-nuts] LT3042, etc. Re: HP E1938A schematics.
In message <20190709053037.2d244406...@ip-64-139-1-69.sjc.megapath.net>, Hal Mu rray writes: >What's the advantage of a PSRR in the MHz range? Is it as simple as reducing >the number and size of the caps needed? The caps have only ever acted as a low-pass filter, to move the noise down in the frequency range of the power-supply regulation. The digital switching noise happens in (pico- and nano-)Coloumbs, not in volts or amps, which means that as the supply voltage decreases, it becomes percentwise larger voltage noise. To deal with that passively you would need bigger caps with better high frequency performance, and lower ESR and more, expensive PCBs (more layers etc.) The trend is therefore to move the corner frequency of the passive low-pass filter higher, that allows you to use ceramic capacitors, instead you must increase the bandwidth of the final power-supply, typically a LDO, and move it physically closer to the load. On high-end kit, it is not uncommon to see a big chip surrounded by a ring of tiny LDO's spaced as little as a centimeter apart along its periphery. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] LT3042, etc. Re: HP E1938A schematics.
>> Not only are they low noise, but they have spectacularly good HF >> rejection across the regulator up to 10s of MHz. > In the 5071A, I wanted high bandwidth PSRR and stumbled across a designer's > manual (HP internal document) for the MMS Modular Measurement System. They > described a regulator with a common base pass transistor and an op amp, with > a bandwidth approaching 1 MHz. I'm used to thinking that the bypass caps on the board will take care of high frequencies. What's the advantage of a PSRR in the MHz range? Is it as simple as reducing the number and size of the caps needed? In this area, is there a significant difference between analog and digital sections? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] LT3042, etc. Re: HP E1938A schematics.
RRR . you are right about drop and noise.. For others not familiar with this behaviour, one thing when looking is PSRR etc on LDOs..take a good look at this value VERSUS dropout / headroom . Most devices are in the toilet when dropout is nigh... In my SDRs I (used) to run 2V around for 1.8V point of load LDO supplies. PSRR 100k went up alot when I bumped the supply rail to 2.2V... On 9/07/2019 10:44 AM, jimlux wrote: On 7/8/19 4:53 PM, Richard (Rick) Karlquist wrote: On 7/8/2019 11:09 AM, jimlux wrote: Not only are they low noise, but they have spectacularly good HF rejection across the regulator up to 10s of MHz. In the 5071A, I wanted high bandwidth PSRR and stumbled across a designer's manual (HP internal document) for the MMS Modular Measurement System. They described a regulator with a common base pass transistor and an op amp, with a bandwidth approaching 1 MHz. Quite state of the art for the time. I copied the design in several 5071A modules. We used it to regulate +5V from the Vicor modules down to ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] LT3042, etc. Re: HP E1938A schematics.
On 7/8/19 4:53 PM, Richard (Rick) Karlquist wrote: On 7/8/2019 11:09 AM, jimlux wrote: Not only are they low noise, but they have spectacularly good HF rejection across the regulator up to 10s of MHz. In the 5071A, I wanted high bandwidth PSRR and stumbled across a designer's manual (HP internal document) for the MMS Modular Measurement System. They described a regulator with a common base pass transistor and an op amp, with a bandwidth approaching 1 MHz. Quite state of the art for the time. I copied the design in several 5071A modules. We used it to regulate +5V from the Vicor modules down to +4.5V working voltage for 100 series ECL or analog. It worked quite well. Now I could replace it with an LT3065. Rick N6RK Barely - I've got bit in the past by coming too close to the LDO minimum voltage. 300mV for those parts, so as long as your +5 had decent regulation, and the ripple didn't drop below 4.8V, and you didn't draw more than 300 mA. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] LT3042, etc. Re: HP E1938A schematics.
On 7/8/2019 11:09 AM, jimlux wrote: Not only are they low noise, but they have spectacularly good HF rejection across the regulator up to 10s of MHz. In the 5071A, I wanted high bandwidth PSRR and stumbled across a designer's manual (HP internal document) for the MMS Modular Measurement System. They described a regulator with a common base pass transistor and an op amp, with a bandwidth approaching 1 MHz. Quite state of the art for the time. I copied the design in several 5071A modules. We used it to regulate +5V from the Vicor modules down to +4.5V working voltage for 100 series ECL or analog. It worked quite well. Now I could replace it with an LT3065. Rick N6RK ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] LT3042, etc. Re: HP E1938A schematics.
On 7/8/19 8:38 AM, Richard (Rick) Karlquist wrote: Regarding the E1938A schematic: Although not references per se, the LT3042/LT3045/LT3045-1 are extremely low noise voltage regulators. Actually, if there are any time nuts who haven't yet heard of these, the data sheets should be considered required reading. Recently, ADI introduced a family of negative regulators that are basically exact mirror images of the positive regulators, right down to the same pin out. The LT3093 is a negative version of the LT3042 and the LT3094 is a negative version of the LT3045-1. ADI has done an outstanding job of supporting the chips with reference designs and PC board layout tips along with evaluation boards. Not only are they low noise, but they have spectacularly good HF rejection across the regulator up to 10s of MHz. I highly recommend them. They appear to be reasonably radiation tolerant, too, although not advertised as such. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
