reg + reference
in [Design]
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From: John Devereux on 30 Mar 2010 06:42 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: > 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. > > 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 > 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. I find NXP documention for the digital/firmware side very good, but the "analog" specifications seem very much an afterthought. ISTR the ADC changed from 1M SPS in the initial publicity to 200k SPS in the datasheet, Its the opposite with the Analog Devices ARMs. They have good analog documentation (and performance) and comparitively underpowered digital peripherals and CPU. They do models targeted at 20mA loop-powered applications. > 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. > > Mixed-signal datasheets come in three sorts: > > Terrible analog specs > > Terrible digital specs > > Terrible specs. > I would say the same applies to the actual parts, too. -- John Devereux
From: Nico Coesel on 30 Mar 2010 14:32 John Devereux <john(a)devereux.me.uk> wrote: >John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: > >> 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: >>> >>>>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 >> 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. > >I find NXP documention for the digital/firmware side very good, but the >"analog" specifications seem very much an afterthought. ISTR the ADC >changed from 1M SPS in the initial publicity to 200k SPS in the Thanks. That means I'm not getting old :-) I also recalled the LCP17xx ADCs to do 1MSPs not 200kHz. Weird. The LPC2000 series ADC can be used up to 500kSPs. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico(a)nctdevpuntnl (punt=.) --------------------------------------------------------------
From: JosephKK on 31 Mar 2010 07:37 On Fri, 26 Mar 2010 18:40:33 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Fri, 26 Mar 2010 17:01:38 -0700 (PDT), "langwadt(a)fonz.dk" ><langwadt(a)fonz.dk> wrote: > >>On 26 Mar., 22:24, John Larkin >><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> On Fri, 26 Mar 2010 19:21:00 GMT, Jan Panteltje >>> >>> <pNaonStpealm...(a)yahoo.com> wrote: >>> >On a sunny day (Fri, 26 Mar 2010 10:19:55 -0700) it happened John Larkin >>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote in >>> ><13rpq5lqd1lj1k9flb9orfr2vcl2tuu...(a)4ax.com>: >>> >>> >>ftp://jjlarkin.lmi.net/V220_reg.JPG >>> >>> >>John >>> >>> >No money for a real current source or current mirror? >>> >Does that 1M depending on beta circuit change a lot over temperature? >>> >Its Vbe will change, so will the Ib. >>> >>> The current into the reference will be more constant than if I just >>> used a resistor with a nominal 0.3 volt drop across it. The BCX71K has >>> a very tight beta spec. It would probably be better than using the >>> current mirror discussed in another thread recently. And we have >>> BCX71Ks in stock for under 4 cents each. >>> >>> The +15 is not very well regulated, and I'm tight for space. >>> >>> I guess I could use a depletion mode fet from +15. That's just one >>> part. The current regulation would be fair, but I wouldn't have any >>> flexibility on setting current. An LND150 is 33 cents, no problem >>> there, but Idss is 1 to 3 mA and it may change a bunch with >>> temperature. >>> >>> Or maybe there exists a 3 volt 3-wire reference that would work from >>> 3.3 volts. >> >>use the ~3.3V as reference, measure a 1.2V reference voltage and >>correct for it? > >I could use a 1.2 volt shunt reference, with a reasonable resistor >from 3.3, and use an opamp to scale the 1.2 up to 3. More parts! The >National low-dropout reference is ideal, if it doesn't oscillate. > >> >>> >>> This will be the ADC voltage reference for an NXP ARM processor. I'm >>> doing a 12-channel 4-20 mA thing, electrically isolated per channel, >>> with an ARM per channel. The ARM and other stuff might need 45 mA or >>> so, less if we can sleep the code a lot. >> >>why not pick an ARM with a build in reference? something like >>stm32... ? >>12 bits too, think the nxp is only 10bits > >The NXP LPC1768 we're going to use has a 12 bit mux'd ADC and a 10 bit >DAC, and all the other stuff like ram, flash, SPI we need. It's a 100 >MHz CPU with single-cycle multiply, pretty impressive for around $7. >We're going to be running a couple of PID loops as fast as the ADC can >feed us data, 100K hits a second maybe. > >Some of the ST parts look nice, but we already have the compiler/jtag >infrastructure in place for the NXP, and we're blinking LEDs, so we'll >stick with that. > >> >>I'm sure analog has some too > >ARM seems to have won the embedded game. Freescale/Coldfire is rumored >to be seriously ill. > >John Could you elucidate on the coldfire being seriously ill? Preferably with references / links, as it may impact my employer.
From: JosephKK on 31 Mar 2010 08:24 On Sat, 27 Mar 2010 08:49:16 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Nico Coesel wrote: >> Joerg <invalid(a)invalid.invalid> wrote: >> >>> It's like press-fit where I sat in a meting where a company pitched it >>> to a client. Tappa-di-tap went my calculator. "I calculated that 3 out >>> of all the contacts will be open. Can you tell us which ones those will >>> be?". The meeting and the sales pitch ended that instant ... >> >> Sorry but that must be some calculating error on your side. All PABXes >> I've seen had press-fit backplanes for a very good reason >> (reliability). But just like soldering and crimping connections >> mounting press-fit is something that needs to be done right. >> > >On the first series it had been done by the pros. Sorry, but my >experience with pressfit is not positive. Not as bad as with wire-wrap >but close. Hmm. My experience with wire-wrap has been uniformly good. Also like soldering and crimping, it must be done right. 30+ years ago i was certified for solder, wire-wrap and crimp.
From: John Larkin on 31 Mar 2010 11:22
On Wed, 31 Mar 2010 04:37:14 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Fri, 26 Mar 2010 18:40:33 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Fri, 26 Mar 2010 17:01:38 -0700 (PDT), "langwadt(a)fonz.dk" >><langwadt(a)fonz.dk> wrote: >> >>>On 26 Mar., 22:24, John Larkin >>><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> On Fri, 26 Mar 2010 19:21:00 GMT, Jan Panteltje >>>> >>>> <pNaonStpealm...(a)yahoo.com> wrote: >>>> >On a sunny day (Fri, 26 Mar 2010 10:19:55 -0700) it happened John Larkin >>>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote in >>>> ><13rpq5lqd1lj1k9flb9orfr2vcl2tuu...(a)4ax.com>: >>>> >>>> >>ftp://jjlarkin.lmi.net/V220_reg.JPG >>>> >>>> >>John >>>> >>>> >No money for a real current source or current mirror? >>>> >Does that 1M depending on beta circuit change a lot over temperature? >>>> >Its Vbe will change, so will the Ib. >>>> >>>> The current into the reference will be more constant than if I just >>>> used a resistor with a nominal 0.3 volt drop across it. The BCX71K has >>>> a very tight beta spec. It would probably be better than using the >>>> current mirror discussed in another thread recently. And we have >>>> BCX71Ks in stock for under 4 cents each. >>>> >>>> The +15 is not very well regulated, and I'm tight for space. >>>> >>>> I guess I could use a depletion mode fet from +15. That's just one >>>> part. The current regulation would be fair, but I wouldn't have any >>>> flexibility on setting current. An LND150 is 33 cents, no problem >>>> there, but Idss is 1 to 3 mA and it may change a bunch with >>>> temperature. >>>> >>>> Or maybe there exists a 3 volt 3-wire reference that would work from >>>> 3.3 volts. >>> >>>use the ~3.3V as reference, measure a 1.2V reference voltage and >>>correct for it? >> >>I could use a 1.2 volt shunt reference, with a reasonable resistor >>from 3.3, and use an opamp to scale the 1.2 up to 3. More parts! The >>National low-dropout reference is ideal, if it doesn't oscillate. >> >>> >>>> >>>> This will be the ADC voltage reference for an NXP ARM processor. I'm >>>> doing a 12-channel 4-20 mA thing, electrically isolated per channel, >>>> with an ARM per channel. The ARM and other stuff might need 45 mA or >>>> so, less if we can sleep the code a lot. >>> >>>why not pick an ARM with a build in reference? something like >>>stm32... ? >>>12 bits too, think the nxp is only 10bits >> >>The NXP LPC1768 we're going to use has a 12 bit mux'd ADC and a 10 bit >>DAC, and all the other stuff like ram, flash, SPI we need. It's a 100 >>MHz CPU with single-cycle multiply, pretty impressive for around $7. >>We're going to be running a couple of PID loops as fast as the ADC can >>feed us data, 100K hits a second maybe. >> >>Some of the ST parts look nice, but we already have the compiler/jtag >>infrastructure in place for the NXP, and we're blinking LEDs, so we'll >>stick with that. >> >>> >>>I'm sure analog has some too >> >>ARM seems to have won the embedded game. Freescale/Coldfire is rumored >>to be seriously ill. >> >>John > >Could you elucidate on the coldfire being seriously ill? Preferably with >references / links, as it may impact my employer. www.google.com. John |