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Does an LM285 voltage reference IC's noise scale with reverse current?

I'll try to find out for myself, but I think having looked at the data sheet and found no obvious answer, I can justify asking here..

The LM285-2.5 reference has wideband noise (10 Hz to 10 KHz) at 120µV when its reverse current is 100µA, according to both the National Semiconductor and Linear Technology data sheets. Neither says what happens at different reverse currents, and the graphs don't allow me to work it out.

Either I'm missing something obvious thart I ought to know (and can't hwlp thinking ought to be spelled out in the data sheet too if it's that important), or it's not different enough at any operating curent to matter. Anyone know which?

Reply to
Lostgallifreyan
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Lostgallifreyan schrieb:

Noise will be dertermined by the input stage, whose operating conditions do not depend on reverse current of the LM385; that is felt by the output stage only. Filtering capacitors integrated on the chip apparently shape the frequency characteristics of the noise, they appear too cut it down above 1kHz to 10kHz. This can be seen from curves in the corresponding LT1004 data sheets. The LT1004-1.2 and -2.5 made by LT and also by TI are the same device with tighter voltage tolerances (other specs and circuit diagram agree) while still affordable. One typically gets +-1mV at room temperature.

If unsatisfied by the actual noise performance of the LT385 load with C or R-C.

Martin.

Reply to
clicliclic

snipped-for-privacy@freenet.de wrote in news: snipped-for-privacy@freenet.de:

Thankyou. That looks complete. I can't help wondering why they specify the noise at a given reverse current though, if it does not depend on it.

Anyway, I'll be filtering with 10K and 1µF before the low noise amp I'm already using (because several inputs will be fed with this reference).

I'll also look at the LT1004, though for this current task the differences between voltages are ok, no worse than between existing references in the rest of the system.

Reply to
Lostgallifreyan

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