reg + reference
in [Design]
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From: John Larkin on 27 Mar 2010 13:49 On Sat, 27 Mar 2010 17:41:32 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Sat, 27 Mar 2010 09:51:08 -0700) it happened John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in ><3kdsq5ld9vp8ohgmg96apb3m3radmho5l7(a)4ax.com>: > >>>Or simply a LM317, I use LM317 for everything, very stable output at low loads. >> >>The TC would be terrible, espacially as it self-heats. I want overall >>channel accuracy of at least 0.1%, and there are other errors to deal >>with, so I can't use a rotten reference. >> >>John > >I did say this before, maybe nobody believes it, >but I had the LM317 on the fluke with no load (or light load actually), >and heated it up with a soldering iron, >the display did not change. Can you quantify the TC? National's spec is 1% over the temp range, whatever that means, which is maybe 20x worse than I'd like. The typical curve on the datasheet just about eats all my error budget. John
From: Joerg on 27 Mar 2010 13:58 John Larkin wrote: > On Sat, 27 Mar 2010 08:47:41 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Fri, 26 Mar 2010 17:22:36 -0700, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> John Larkin wrote: >>>>> On Fri, 26 Mar 2010 15:36:09 -0700, John Larkin >>>>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> >>>>>> On Fri, 26 Mar 2010 14:34:19 -0700, Joerg <invalid(a)invalid.invalid> >>>>>> wrote: >>>>>> >>>>>>> John Larkin wrote: >>>>>>>> ftp://jjlarkin.lmi.net/V220_reg.JPG >>>>>>>> >>>>>>> Just curious, why not replace all this with one of these: >>>>>>> >>>>>>> http://www.analog.com/static/imported-files/Data_Sheets/ADR01_02_03_06.pdf >>>>>>> >>>>>>> Much less space, cheaper. Unless you need the 3.3V somewhere. >>>>>> Yes, I need 3.3 to run an ARM processor, 40 mA or so maybe. >>>>>> >>>>>> The ADR could run off the +15, so maybe that's a better way to go. It >>>>>> would cost a little more, but the TC would be a lot better. >>>>>> >>>>>> Maybe I'll do that, the LM1117 for power and the ADR for the >>>>>> reference. >>>>>> >>>>>> Wait! LM4120 will work. +3 ref with 120 mV dropout! >>>>>> >>>>>> >>>>>> John >>>>> And of course, the LM4120 is a stability land-mine of its own. >>>>> >>>>> ThestandardapplicationcircuitfortheLM4120isshownin >>>>> Figure1.Itisdesignedtobestablewithceramicoutput >>>>> capacitorsintherangeof0.022�Fto0.047�F.Notethat >>>>> 0.022�Fistheminimumrequiredoutputcapacitor.These >>>>> capacitorstypicallyhaveanESRofabout0.1to0.5. >>>>> SmallerESRcanbetolerated,howeverlargerESRcannot. >>>>> Theoutputcapacitorcanbeincreasedtoimproveloadtran- >>>>> sientresponse,uptoabout1�F.However,valuesabove >>>>> 0.047�Fmustbetantalum.Withtantalumcapacitors,inthe >>>>> 1�Frange,asmallcapacitorbetweentheoutputandthe >>>>> referencepinisrequired.Thiscapacitorwilltypicallybein >>>>> the50pFrange.Caremustbetakenwhenusingoutput >>>>> capacitorsof1�Forlarger.Theseapplicationmustbethor- >>>>> oughlytestedovertemperature,lineandload. >>>>> >>>>> >>>>> Thanks, National. >>>>> >>>> I was just gonna tell you. If there was one I'd have a bumper sticker on >>>> my car "LDO, no, no, no!" >>>> >>>> My advice to clients there is always the same, don't ever use an LDO >>>> unless there is absolutely no other way (and in my 25 years on the beat >>>> there always was). No matter what the marketeers sing from the trees. >>> Unless I work off the +15, which has its own complications, I need >>> this LDO voltage reference. After all, they say it's stable over - >>> wait for it - a 2:1 load capacitor range! Assuming you get the ESR >>> right. >>> >> And nothing seems to be guaranteed. When I read page 9 in the datasheet >> I am beginning to feel sick. > > Cute, how they say the compensation capacitor is in the "50 pF range" > and how they expect *me* to compensate and extensively > temperature/line/load test *their* part to ensure stability. I'm > expected to do a couple thousand dollars worth of testing on their > behalf. > > National is very sloppy as regards stability of lots of their parts. > Which is why I haven't designed in any of their power parts lately, except legacy stuff such as the LM317. LTC is pretty good, very responsive, great support engineers who really know electronics. Plus LTSpice models for just about anything and that alone ist worth a ton, has won them many design-ins on my part. Although I recently unearthed an ugly power-up bug in a part but that was a comparator, LT6700. But they went to the ground of it, confirmed it, fessed up, and apologized. Way to go. > >> Why does working off of the +15V have complications? > > I'd need a series reference that can tolerate unregulated +15, so I'd > probably have to preregulate into it... more parts. Shunt regs have > mediocre TCs and would get not-very-constant current if I just use a > resistor from +15. I expect that my 4-20 mA (really 0 to 25 maybe) > load and uP power patterns will whack the DC-DC output voltage all > over the place. > > There will be 12 channels per VME board, so I want low parts count and > cheap parts! > An RC filter or capacitor multiplier should suffice. Input ripple rejection is usually huge as long as it doesn't contain high frequency stuff. Or use one preregulator per board. Or even better, one reference per board. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 27 Mar 2010 14:52 On Sat, 27 Mar 2010 10:58:04 -0700, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Sat, 27 Mar 2010 08:47:41 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> John Larkin wrote: >>>> On Fri, 26 Mar 2010 17:22:36 -0700, Joerg <invalid(a)invalid.invalid> >>>> wrote: >>>> >>>>> John Larkin wrote: >>>>>> On Fri, 26 Mar 2010 15:36:09 -0700, John Larkin >>>>>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>> >>>>>>> On Fri, 26 Mar 2010 14:34:19 -0700, Joerg <invalid(a)invalid.invalid> >>>>>>> wrote: >>>>>>> >>>>>>>> John Larkin wrote: >>>>>>>>> ftp://jjlarkin.lmi.net/V220_reg.JPG >>>>>>>>> >>>>>>>> Just curious, why not replace all this with one of these: >>>>>>>> >>>>>>>> http://www.analog.com/static/imported-files/Data_Sheets/ADR01_02_03_06.pdf >>>>>>>> >>>>>>>> Much less space, cheaper. Unless you need the 3.3V somewhere. >>>>>>> Yes, I need 3.3 to run an ARM processor, 40 mA or so maybe. >>>>>>> >>>>>>> The ADR could run off the +15, so maybe that's a better way to go. It >>>>>>> would cost a little more, but the TC would be a lot better. >>>>>>> >>>>>>> Maybe I'll do that, the LM1117 for power and the ADR for the >>>>>>> reference. >>>>>>> >>>>>>> Wait! LM4120 will work. +3 ref with 120 mV dropout! >>>>>>> >>>>>>> >>>>>>> John >>>>>> And of course, the LM4120 is a stability land-mine of its own. >>>>>> >>>>>> ThestandardapplicationcircuitfortheLM4120isshownin >>>>>> Figure1.Itisdesignedtobestablewithceramicoutput >>>>>> capacitorsintherangeof0.022�Fto0.047�F.Notethat >>>>>> 0.022�Fistheminimumrequiredoutputcapacitor.These >>>>>> capacitorstypicallyhaveanESRofabout0.1to0.5. >>>>>> SmallerESRcanbetolerated,howeverlargerESRcannot. >>>>>> Theoutputcapacitorcanbeincreasedtoimproveloadtran- >>>>>> sientresponse,uptoabout1�F.However,valuesabove >>>>>> 0.047�Fmustbetantalum.Withtantalumcapacitors,inthe >>>>>> 1�Frange,asmallcapacitorbetweentheoutputandthe >>>>>> referencepinisrequired.Thiscapacitorwilltypicallybein >>>>>> the50pFrange.Caremustbetakenwhenusingoutput >>>>>> capacitorsof1�Forlarger.Theseapplicationmustbethor- >>>>>> oughlytestedovertemperature,lineandload. >>>>>> >>>>>> >>>>>> Thanks, National. >>>>>> >>>>> I was just gonna tell you. If there was one I'd have a bumper sticker on >>>>> my car "LDO, no, no, no!" >>>>> >>>>> My advice to clients there is always the same, don't ever use an LDO >>>>> unless there is absolutely no other way (and in my 25 years on the beat >>>>> there always was). No matter what the marketeers sing from the trees. >>>> Unless I work off the +15, which has its own complications, I need >>>> this LDO voltage reference. After all, they say it's stable over - >>>> wait for it - a 2:1 load capacitor range! Assuming you get the ESR >>>> right. >>>> >>> And nothing seems to be guaranteed. When I read page 9 in the datasheet >>> I am beginning to feel sick. >> >> Cute, how they say the compensation capacitor is in the "50 pF range" >> and how they expect *me* to compensate and extensively >> temperature/line/load test *their* part to ensure stability. I'm >> expected to do a couple thousand dollars worth of testing on their >> behalf. >> >> National is very sloppy as regards stability of lots of their parts. >> > >Which is why I haven't designed in any of their power parts lately, >except legacy stuff such as the LM317. LTC is pretty good, very >responsive, great support engineers who really know electronics. Plus >LTSpice models for just about anything and that alone ist worth a ton, >has won them many design-ins on my part. Although I recently unearthed >an ugly power-up bug in a part but that was a comparator, LT6700. But >they went to the ground of it, confirmed it, fessed up, and apologized. >Way to go. Yes, LTC is great. And LT Spice is a gift to the world. > >> >>> Why does working off of the +15V have complications? >> >> I'd need a series reference that can tolerate unregulated +15, so I'd >> probably have to preregulate into it... more parts. Shunt regs have >> mediocre TCs and would get not-very-constant current if I just use a >> resistor from +15. I expect that my 4-20 mA (really 0 to 25 maybe) >> load and uP power patterns will whack the DC-DC output voltage all >> over the place. >> >> There will be 12 channels per VME board, so I want low parts count and >> cheap parts! >> > >An RC filter or capacitor multiplier should suffice. Input ripple >rejection is usually huge as long as it doesn't contain high frequency >stuff. Or use one preregulator per board. Or even better, one reference >per board. Sadly, all 12 channels are individually floating. It's looking like the safest thing to do is use an LM1117 to make about 3.4 volts - close enough to 3.3 - and use a ca 500 ohm resistor into an LM4040-3.0 or equivalent bandgap with a 10 uF ceramic bypass. Typical TC will be about 15 PPM (guaranteed is not as good, but not lethally bad), sensitivity to 1117 output is pretty good (500 ohms into Zd~~1 ohm), and it's simple and cheap and most important, it's safe. That out of the way, my next task is to explode some SSRs. Certain user abuse modes will put, say, 50 volts across an ON-state SSR. The ARM will sense the hazard and turn off the SSR, so it will have to tolerate the abuse for a millisecond maybe. I'm considering some Clare 8-ohm, 100 volt, 150 mA parts. So what happens if you turn them on and put a bunch of voltage across them? I love to test parts to destruction. John
From: Nico Coesel on 27 Mar 2010 15:06 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Sat, 27 Mar 2010 14:21:15 GMT, nico(a)puntnl.niks (Nico Coesel) >wrote: > >>John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Fri, 26 Mar 2010 14:34:19 -0700, Joerg <invalid(a)invalid.invalid> >>>wrote: >>> >>>>John Larkin wrote: >>>>> ftp://jjlarkin.lmi.net/V220_reg.JPG >>>>> >>>> >>>>Just curious, why not replace all this with one of these: >>>> >>>>http://www.analog.com/static/imported-files/Data_Sheets/ADR01_02_03_06.pdf >>>> >>> >>>>Much less space, cheaper. Unless you need the 3.3V somewhere. >>> >>>Yes, I need 3.3 to run an ARM processor, 40 mA or so maybe. >> >>AFAIK the LPC1768 can run on lower voltages as well like down to 2.6V. >>Not at full speed ofcourse. 40mA may be too optimistic though. > >We figure on sleeping at least half the time in operating mode. I'm >using a 1-watt unregulated Murata sip DC-DC converter to power a >channel, 12 volts in and +-15 out. The +-15 becomes floating ground, >+15 to power the ARM, and +30 for the 4-20 mA current loop. So I have >enough power to run the ARM full-blast during initialization, but not >enough to output 20 mA and run the ARM at max. I would perfer to not >add a switcher to make 3.3, or to add a lot of parts of any sort. We >don't have time for custom magnetics: concept-to-shipping target is 60 >days. Ever thought about these to make brew a multi-output converter: http://catalogue.we-online.com/kataloge/eisos/index.php?language=en&key=Transformer%2FPower%2FKatalog%2FWE-FLEX I still don't understand why you want seperated floating channels. Why not take the inputs through a differential amplifier with a huge common mode range and use one controller? >Luckily, VME does have a lot of air flow. > >> >>>The ADR could run off the +15, so maybe that's a better way to go. It >>>would cost a little more, but the TC would be a lot better. >>> >>>Maybe I'll do that, the LM1117 for power and the ADR for the >>>reference. >>> >>>Wait! LM4120 will work. +3 ref with 120 mV dropout! >> >>Be sure to decouple the reference properly. The ADC sinks quite some >>current from the reference pin when sampling. > >The LM4120 allows me a maximum of 0.047 uF! > >The NXP documentation for this chip, around 1K pages of it, is >horrible. We can find no mention of how much current the Vref pin The amount of current on Vref depends on the ADC's sampling frequency. You can also look at the LPC2000 datasheet to get an idea. >uses. There's also a pin called, if I recall, Vcc(Reg)(3V3) whose >function is unknown. Got any idea? Kyle must not either, since on >their eval board they run it to a jumper header, making it our >problem. Vcc(reg) powers the on-chip DC-DC converter to make 1.8 volts for the core. >The NXP documentation has roughly 1e6 syntactically-challenged words >but not a single application circuit. They should have the schematic >and code for a minimal LED blinker. Thats where the Keil boards + example code kick in. Although I must warn that the Keil example code needs a lot of brushing up before its actually usefull. >Mixed-signal datasheets come in three sorts: > > Terrible analog specs > Terrible digital specs > Terrible specs. NXP is a bit slow on releasing final specifications. Did you download the latest datasheets? -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico(a)nctdevpuntnl (punt=.) --------------------------------------------------------------
From: Joerg on 27 Mar 2010 15:21
John Larkin wrote: > On Sat, 27 Mar 2010 10:58:04 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Sat, 27 Mar 2010 08:47:41 -0700, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> John Larkin wrote: >>>>> On Fri, 26 Mar 2010 17:22:36 -0700, Joerg <invalid(a)invalid.invalid> >>>>> wrote: >>>>> >>>>>> John Larkin wrote: >>>>>>> On Fri, 26 Mar 2010 15:36:09 -0700, John Larkin >>>>>>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>>> >>>>>>>> On Fri, 26 Mar 2010 14:34:19 -0700, Joerg <invalid(a)invalid.invalid> >>>>>>>> wrote: >>>>>>>> >>>>>>>>> John Larkin wrote: >>>>>>>>>> ftp://jjlarkin.lmi.net/V220_reg.JPG >>>>>>>>>> >>>>>>>>> Just curious, why not replace all this with one of these: >>>>>>>>> >>>>>>>>> http://www.analog.com/static/imported-files/Data_Sheets/ADR01_02_03_06.pdf >>>>>>>>> >>>>>>>>> Much less space, cheaper. Unless you need the 3.3V somewhere. >>>>>>>> Yes, I need 3.3 to run an ARM processor, 40 mA or so maybe. >>>>>>>> >>>>>>>> The ADR could run off the +15, so maybe that's a better way to go. It >>>>>>>> would cost a little more, but the TC would be a lot better. >>>>>>>> >>>>>>>> Maybe I'll do that, the LM1117 for power and the ADR for the >>>>>>>> reference. >>>>>>>> >>>>>>>> Wait! LM4120 will work. +3 ref with 120 mV dropout! >>>>>>>> >>>>>>>> >>>>>>>> John >>>>>>> And of course, the LM4120 is a stability land-mine of its own. >>>>>>> >>>>>>> ThestandardapplicationcircuitfortheLM4120isshownin >>>>>>> Figure1.Itisdesignedtobestablewithceramicoutput >>>>>>> capacitorsintherangeof0.022�Fto0.047�F.Notethat >>>>>>> 0.022�Fistheminimumrequiredoutputcapacitor.These >>>>>>> capacitorstypicallyhaveanESRofabout0.1to0.5. >>>>>>> SmallerESRcanbetolerated,howeverlargerESRcannot. >>>>>>> Theoutputcapacitorcanbeincreasedtoimproveloadtran- >>>>>>> sientresponse,uptoabout1�F.However,valuesabove >>>>>>> 0.047�Fmustbetantalum.Withtantalumcapacitors,inthe >>>>>>> 1�Frange,asmallcapacitorbetweentheoutputandthe >>>>>>> referencepinisrequired.Thiscapacitorwilltypicallybein >>>>>>> the50pFrange.Caremustbetakenwhenusingoutput >>>>>>> capacitorsof1�Forlarger.Theseapplicationmustbethor- >>>>>>> oughlytestedovertemperature,lineandload. >>>>>>> >>>>>>> >>>>>>> Thanks, National. >>>>>>> >>>>>> I was just gonna tell you. If there was one I'd have a bumper sticker on >>>>>> my car "LDO, no, no, no!" >>>>>> >>>>>> My advice to clients there is always the same, don't ever use an LDO >>>>>> unless there is absolutely no other way (and in my 25 years on the beat >>>>>> there always was). No matter what the marketeers sing from the trees. >>>>> Unless I work off the +15, which has its own complications, I need >>>>> this LDO voltage reference. After all, they say it's stable over - >>>>> wait for it - a 2:1 load capacitor range! Assuming you get the ESR >>>>> right. >>>>> >>>> And nothing seems to be guaranteed. When I read page 9 in the datasheet >>>> I am beginning to feel sick. >>> Cute, how they say the compensation capacitor is in the "50 pF range" >>> and how they expect *me* to compensate and extensively >>> temperature/line/load test *their* part to ensure stability. I'm >>> expected to do a couple thousand dollars worth of testing on their >>> behalf. >>> >>> National is very sloppy as regards stability of lots of their parts. >>> >> Which is why I haven't designed in any of their power parts lately, >> except legacy stuff such as the LM317. LTC is pretty good, very >> responsive, great support engineers who really know electronics. Plus >> LTSpice models for just about anything and that alone ist worth a ton, >> has won them many design-ins on my part. Although I recently unearthed >> an ugly power-up bug in a part but that was a comparator, LT6700. But >> they went to the ground of it, confirmed it, fessed up, and apologized. >> Way to go. > > > Yes, LTC is great. And LT Spice is a gift to the world. > No free lunch for the other mfgs. AFAIK they have some confidential hooks in there like gated oscillator code that SPICE normally doesn't do. Since the other mfgs can't touch that LTC has secured a nice chunk of the market. If a client needs hi-rel and a design that's vetted as far as possible before prototyping I always try to find an LTC part. I just completed another one two days ago and the sims raised the office temperature by a couple degree which is kind of nice this time of the year. > >>>> Why does working off of the +15V have complications? >>> I'd need a series reference that can tolerate unregulated +15, so I'd >>> probably have to preregulate into it... more parts. Shunt regs have >>> mediocre TCs and would get not-very-constant current if I just use a >>> resistor from +15. I expect that my 4-20 mA (really 0 to 25 maybe) >>> load and uP power patterns will whack the DC-DC output voltage all >>> over the place. >>> >>> There will be 12 channels per VME board, so I want low parts count and >>> cheap parts! >>> >> An RC filter or capacitor multiplier should suffice. Input ripple >> rejection is usually huge as long as it doesn't contain high frequency >> stuff. Or use one preregulator per board. Or even better, one reference >> per board. > > > Sadly, all 12 channels are individually floating. > > It's looking like the safest thing to do is use an LM1117 to make > about 3.4 volts - close enough to 3.3 - and use a ca 500 ohm resistor > into an LM4040-3.0 or equivalent bandgap with a 10 uF ceramic bypass. > Typical TC will be about 15 PPM (guaranteed is not as good, but not > lethally bad), sensitivity to 1117 output is pretty good (500 ohms > into Zd~~1 ohm), and it's simple and cheap and most important, it's > safe. > Ugly, but hey, if it works it works. > That out of the way, my next task is to explode some SSRs. Certain > user abuse modes will put, say, 50 volts across an ON-state SSR. The > ARM will sense the hazard and turn off the SSR, so it will have to > tolerate the abuse for a millisecond maybe. I'm considering some Clare > 8-ohm, 100 volt, 150 mA parts. So what happens if you turn them on and > put a bunch of voltage across them? > A hard 50V with almost zero source resistance? Probably ... *PHUT*. If it's the small CPC1008 OptoMOS relays they are slow so 1msec is normal for them. But as usual the datasheet has scant information, for example no SOA data. Without that information it's hard to say for sure even if a few of them test ok. http://media.digikey.com/pdf/Data%20Sheets/Clare%20PDFs/CPC1008N.pdf > I love to test parts to destruction. > One of our lab/office dogs doesn't. Whenever I do stress testing and something goes poof she scurries out of the lab, turns around at the door, gives me the look, goes to the farthest corner of the office next door and plops herself onto a pillow with a deliberately loud sigh. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |