Precision Resistors, low tempco

Here’s a couple sources for precision resistors.

One source seems to provide a great price/performance trade, the other is really the best quality resistor you’ll be able to buy. BUT precision low drift resistor arrays require careful inspection of the data sheet. Here’s a couple examples.

Recently I noticed that Maxim IC, (famous makers of 5V powered RS232 interface chips), have begin selling a pair of precise resistors in a SOT23 package, at an attractive price.

This family of parts, the MAX5491, claims to have 2ppm/degC resistor to resistor drift of the pair in the same package. Take care – sometimes the large print giveth, and the small print taketh away – the absolute tempco is spec’d as 35ppm/degC, so if you compare two different individual SOT23 units with each other, they may drift more that that nice small 2ppm value at the top of the spec sheet!

link to the Maxim-IC precision resistor array MAX5491 data sheet

For better matching, the VFCD1505 parts made by Vishay, also available at DigiKey, are spec’d for 0.2ppm/degC drift, or 10X better than the Maxim parts (and, well, about 5.7X the price, at $20/qnty 1, vs the $3.50 qnty 1 at DigiKey).

link to the Vishay VFCD1505 precision resistor data sheets

I like that Vishay also details subtle values such as ‘voltage coefficient’ and the current noise (or sometimes called ‘excess noise’, noise that is beyond the thermal noise of the resistor value).

The specifications of the Vishay parts are about where the state of the art is for actual resistors you can buy. Better resistors can be found only at NIST.

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