[time-nuts] TAPR TICC boxed (input protection)
davidwhess at gmail.com
Tue Apr 4 14:05:39 EDT 2017
Low current measurements take a lot of time on the automatic test
equipment and time in this case is measured in seconds. The same
applies to low frequency noise.
For an example, take a look at the National (now TI) LMC6001 and
Unlike National, TI does not care about input bias current in their
selection guides so you will have to look that up in the datasheets:
The difference in the parts is that the LMC6001 is tested for an Ib of
25fA and below and this is reflected in the price which is $5.76
instead of the $0.83 of the LMC6081.
Right about the time that the LMC6001 was released, Robert Pease wrote
some articles talking about the bias current testing and the
The same thing applies to all of those small signal transistors with
25, 50, and 100nA leakage specifications. Those numbers are simply
good enough for typical applications and what the tester can handle in
the time allotted and have nothing to do with the actual transistor
So collector-base junctions make good low leakage high voltage diodes
although they are slow which does not normally matter for an input
protection circuit and may even be preferable. Emitter-base junctions
make good low leakage fast diodes but with low breakdown voltages.
The cheapest guaranteed low leakage diode is probably some variety of
4117/4118/4119 n-channel JFET.
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