[volt-nuts] Matched resistors

[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_-_Jahn at 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 at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/volt-nuts
> and follow the instructions there.
>