[volt-nuts] Matched resistors

Andreas Jahn Andreas_-_Jahn at t-online.de
Fri Jul 18 01:37:30 EDT 2014

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 
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 
(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


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

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