ADUC7020
in [Design]
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From: MooseFET on 2 Jun 2010 11:58 Is there anyone here who knows all about the ADUC7020? I'm about to give up on getting an answer from Analog. There is one line in the whole data sheet that makes me believe that you can make the DACs update on a reload of Timer1 but nothing about the specific timing or any details. Does anyone know?
From: John Larkin on 2 Jun 2010 12:14 On Wed, 2 Jun 2010 08:58:27 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote: > >Is there anyone here who knows all about the ADUC7020? > >I'm about to give up on getting an answer from Analog. Hey, I don't want to hear about your problems... I'm trying to get an answer from Analog Devices about the AD7699! I think I have finally got them to admit that reference drift does *not* explain zero offset TC. > >There is one line in the whole data sheet that makes me believe that >you can make the DACs update on a reload of Timer1 but nothing >about the specific timing or any details. The interfaces and datasheets of mixed-signal products are typically horrible. John
From: MooseFET on 2 Jun 2010 18:53 On Jun 2, 9:14 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Wed, 2 Jun 2010 08:58:27 -0700 (PDT), MooseFET <kensm...(a)rahul.net> > wrote: > > > > >Is there anyone here who knows all about the ADUC7020? > > >I'm about to give up on getting an answer from Analog. > > Hey, I don't want to hear about your problems... I'm trying to get an > answer from Analog Devices about the AD7699! I think I have finally > got them to admit that reference drift does *not* explain zero offset > TC. Oh-oh. Guess who else had looked at that datasheet. Lucky me, I had already decided "perhaps not" If I have to use just an ARM with external converters, odds are I'd go with Linear's converters. I had been looking at the AD 8 channel DAC and a 14 bit ADC. > >There is one line in the whole data sheet that makes me believe that > >you can make the DACs update on a reload of Timer1 but nothing > >about the specific timing or any details. > > The interfaces and datasheets of mixed-signal products are typically > horrible. This is one place where the folks at Silabs do a fairly good job. They document the analog parts as though they were external things. It is like they get the guy who does the analog section to write up something that goes to the technical writers. > > John
From: Phil Hobbs on 4 Jun 2010 15:07 On 6/2/2010 12:14 PM, John Larkin wrote: > On Wed, 2 Jun 2010 08:58:27 -0700 (PDT), MooseFET<kensmith(a)rahul.net> > wrote: > >> >> Is there anyone here who knows all about the ADUC7020? >> >> I'm about to give up on getting an answer from Analog. > > Hey, I don't want to hear about your problems... I'm trying to get an > answer from Analog Devices about the AD7699! I think I have finally > got them to admit that reference drift does *not* explain zero offset > TC. > Hmm. A customer of mine is planning to use that part to digitize very low frequency stuff--seismometer and tiltmeter data and so on...could you say a bit more about what the issues are? >> >> There is one line in the whole data sheet that makes me believe that >> you can make the DACs update on a reload of Timer1 but nothing >> about the specific timing or any details. > > The interfaces and datasheets of mixed-signal products are typically > horrible. CCD chips are the worst, IME. Cheers Phil Hobbs > -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: John Larkin on 4 Jun 2010 15:39
On Fri, 04 Jun 2010 15:07:35 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >On 6/2/2010 12:14 PM, John Larkin wrote: >> On Wed, 2 Jun 2010 08:58:27 -0700 (PDT), MooseFET<kensmith(a)rahul.net> >> wrote: >> >>> >>> Is there anyone here who knows all about the ADUC7020? >>> >>> I'm about to give up on getting an answer from Analog. >> >> Hey, I don't want to hear about your problems... I'm trying to get an >> answer from Analog Devices about the AD7699! I think I have finally >> got them to admit that reference drift does *not* explain zero offset >> TC. >> >Hmm. A customer of mine is planning to use that part to digitize very >low frequency stuff--seismometer and tiltmeter data and so on...could >you say a bit more about what the issues are? I am seeing a huge amount of zero drift with temperature. Chris Augusta, the guy at ADI who wrote the datasheet, helped me find the problem. I now owe him beers. In bipolar mode, you apply a differential input between a pair of pins, like IN0 and IN1, pins 16 and 17, for instance. Turns out that the IN1 pin must be within +-0.1 volts of Vref/2 or the zero TC goes to hell. It says that on the datasheet, but I missed it somehow. I'd got too used to pseudo-differential charge-balance ADCs actually having lots of common-mode rejection. My bad, I guess. On my board, I'm using a 2.5 volt bandgap and a C-load follower opamp to generate the Vcm used by all 16 ADCs. I can change that to a 2.048 bandgap and get legal again. Here's the board: http://www.highlandtechnology.com/DSS/V490DS.html Now I can crank the accuracy specs up to less embarassing numbers. John |