Texas Instruments' LM4041 – When a Zener Just Doesn’t Cut it
Finding a good voltage reference is as difficult as asking a cigar afficionado for the perfect smoke – the answer depends on the mood and the character of the individual queried. TI’s LM4041 series provides a “common sense” solution for all those not desperate for the highest accuracy.
From a technical point of view, the LM4041 is but a better zener diode available in various three- and five-terminal SMD housings. This means that the responsibility for current limitation falls solely in the hands of the user – directly connecting the part to a high, unregulated DC voltage rail leads to catastrophic failure. Instead, the simplest possible approach involves a shunt regulator as shown in figure one.
The protection resistor limits the current flowing through the reference
TI provides an adjustable version of the LM4041, which works via a set of external feedback resistors. In that case, total accuracy depends on both the resistors and the LM4041 – a situation which can become interesting as thermal drift takes place.
In general, TI promises an original accuracy of their 0.1 or 0.2% as shipped, with detailed data given on the influence of temperature changes on system performance. Sadly, TI does not specify much in terms of long-time stability: the maximum information given in the datasheet claims a 125ppm change in voltage output over 1000 hours.
Nevertheless, the part – for sure – is interesting and should be at the back of your mind when working on data acquisition systems.