Andreas, Thanks for the information. Do you have the drift chart, etc. posted anywhere? that would be very interesting reading.
Thanks, Randy On Fri, Jul 18, 2014 at 10:11 PM, Andreas Jahn <andreas_-_j...@t-online.de> wrote: > Hello Randy, > > I think the only difference is in oscillator section (and thus power > consumption) > and of cause the TSSOP-package. > The LTC1043 is easily available from stock e.g. from digikey. > The LTC6943 is more difficult to get. > Within the Keithley 2002 LTC1043 is used. > http://www.eevblog.com/forum/testgear/keithley-2002-8-5- > digit-dmm-review-and-teardown/ > http://dev.xdevs.com/projects/kei2002/repository/entry/ > photos/K1/small/K2002_1-2251.jpg > > I have added a drift chart with longterm drift data. > Note: the drift is for the whole measurement arrangement. > It consists of 3 7V references (2 LTZ1000A and 1 LM399) > measured via a LTC1043 divider with a 24 bit LTC2400 ADC with > temperature compensated voltage reference AD586LQ. > So most of the drift is related to the AD586LQ reference. > (X-axis is in days, Y-axis in ppm) > > I get around 2 ppm drift for the LTZ1000A over 1 year > which I guess is mostly humidity related > from the ADC printed cirquit board + AD586 reference drift > and usually below 0.25 ppm standard deviation over 1000 hours. (42 days). > All at unstabilized room temperature. > I guess with resistors you will need ovenized temperature stabilisation to > achieve this. > > with best regards > > Andreas > > Am 19.07.2014 05:57, schrieb Randy Evans: > > Andreas, >> >> That is good information, I appreciate it. I have contacted LT >> application >> support but they have yet to get back to me on my questions except they >> did >> recommend to use the LTC6943 instead of the LTC1043. Later generation I >> guess. >> >> I think i am going to try both the LTC6943 and the LT5400 resistor array >> and characterize them. The LT5400 matching ratio looks pretty good over >> temp (0.2ppm/C) but the absolute resistor change over temp is -10 to +25 >> ppm/C, a little larger than I would like for the circuit I am using. >> >> Randy >> >> >> On Thu, Jul 17, 2014 at 10:37 PM, Andreas Jahn < >> andreas_-_j...@t-online.de> >> wrote: >> >> Hello Randy, >>> >>> I am using the LTC1043 in 1/2 VIN or 1/3 VIN configuration. >>> A matching of the caps is not necessary. >>> In the 1/2 VIN or 1/3 VIN configuration a matching would give >>> the advantage that the settling time of the cirquit is reduced. >>> But in 2* VIN or inverting configuration a matching gives no advantage. >>> So perhaps it is better to put a 1/2 VIN divider into a feedback loop. >>> >>> The most important point: you will need a low leakage buffer amplifier at >>> the output. >>> The caps should be low leakage foil capacitors. (polypropylene would be >>> best). >>> The ESR is negligible against the switch resistance of around 1000 Ohms >>> And dielectric absorption would also affect only settling time. >>> >>> In 1/2 VIN configuration I am using cheap small mylar capacitors (WIMA >>> MKS02) >>> (isolation time constant is given only with >1250 sec (3000 sec typ)). >>> Buffer amplifier is a LTC1050. >>> The circuit is very stable over temperature (10 - 40 deg C). >>> The absolute amplification error is usually some ppm lower than exact 2:1 >>> value. >>> (depends somewhat on the pinning which is used so I am not shure wether >>> the pins are mixed up regarding the charge compensation) >>> >>> So I dont know wether the ±1 ppm is more a stability figure than a >>> absolute value. >>> Even polypropylene capacitors do not change the amplification error. >>> >>> With best regards >>> >>> Andreas >>> >>> Am 17.07.2014 17:26, schrieb Randy Evans: >>> >>> Frank, >>>> >>>> The high cost is my concern, although high performance demands high >>>> price >>>> typically. I am trying to double the voltage reference from either an >>>> LM399 or LTZ1000, hence the need for precision matched resistors for a >>>> x2 >>>> non-inverting amplifier (using a LT1151 precision op amp). An >>>> alternative >>>> I am investigating is using the LTC1043 in a voltage doubling circuit as >>>> shown in Linear Technology app note AN 42, page 6, Figure 16. It states >>>> that Vout = 2xVin ± 5 ppm. I am less concerned about the absolute >>>> >>>> accuracy than I am about the long term stability. I assume that a high >>>> quality capacitor is required (low leakage, low ESR, low dielectric >>>> absorbtion, etc.) but the circuit does not appear to be dependent on the >>>> absolute value of the capacitors. I'm not sure if the two 1uF caps >>>> need >>>> to be matched. If they do then that would be a show stopper. >>>> >>>> Does anyone have any experience using the LTC1043 in such a circuit? >>>> >>>> Thanks, >>>> >>>> Randy >>>> >>>> _______________________________________________ >>>> >>> volt-nuts mailing list -- volt-nuts@febo.com >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >>> mailman/listinfo/volt-nuts >>> and follow the instructions there. >>> >>> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/volt-nuts >> and follow the instructions there. >> > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
