[volt-nuts] Trimming the LTZ1000 tempco
bruce.griffiths at xtra.co.nz
Fri Oct 7 09:19:05 UTC 2011
There's little point in adding the tempco compensation resistor if you
do that as your proposed connection essentially eliminates the
additional correction provided by the resistor.
There's no way of avoiding the sensitivity to the value of this resistor
if this method of tempco trimming is used.
However if a +50ppm/K LTZ1000 residual tempco (with the tempco trim
resistor = 0) is typical, then the sensitivity will only be about 10% or
so of that esstimated by Adreas.
> I would take the output voltage between pins 3 and 7 and leave the
> resistor "outside". There is already a diode between the op-amp output
> and the zener cathode and the diode must be much less time and
> temperature stable than a resistor.
> Or did I misunderstand something again?
> 2011/10/7, Andreas Jahn<Andreas_-_Jahn at t-online.de>:
>> But consider: a resistance change on the 200R resistor of page 6
>> will directly affect output voltage. 200R * 5mA = 1V.
>> A 100 ppm change of the 200R Resistor has a 1V/8.2V
>> = 12 ppm change on output voltage.
>> All other resistors have below 1ppm change with 100ppm resistance change.
>> So the 200 Ohms resistor will be the most
>> critical for tempco and ageing in the whole system.
>> So in my opinion its only worth to consider if you
>> really need to save the 20-30 mA for the heater.
>> With best regards
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