The best resistors you can get

Let’s just say you need the best resistor you can get, in terms of precision and stability, in a low-power rating. What can you get?

Under the topic of Resistor, Fixed, Single, Surface Mount, the SiliconExpert Technologies website (www.siliconexpert.com) lists 2,389,592 parts — and that’s just SMT. There’s another 1,807,032 part numbers under single through-hole. That’s a lot of resistors to look over. Let me help.

If you are even thinking you will need a precision resistor in a surface mount package, use the 0805 SMT size — for one reason or another, there seems to be more availability in that size, though 0603 and 1206 are also very available.

Bourns offers the CRT series of 0.01% tolerance SMT resistors with a ±2 ppm to ±5 ppm/°C TCR, depending on size and value. It comes in 0402 to 1206 sizes, with the 0805 size having 2 ppm TCR available from 49.9 Ω to 30 KΩ. An example part number is the CRT0805-PV-3301ELF 3.3 KΩ 0805 with 0.01% tolerance and 5 ppm TCR is just $1.76 ea in single reel quantities.

Fig. 1: The Bourns CRT series resistor

Vishay Precision Group offers a number of precision resistors (way too many, I would think). But if you are talking precision, the Vishay Z-series is tops, with 0.005% tolerance and ± 0.05 ppm/°C nominal (0 °C to +60 °C) TCR and ± 0.2 ppm/°C nominal (-55 °C to +125 °C), This is a foil resistor and, if you can believe it, the Z-Series part number begins with a Y. Example part number Y1453100R000V is a 100Ω device rated for 0.6 W at 70°C. This 0.300 x 0.326 x 0.1.5-inch radial through-hole resistor is available with 5.00 Ω to 100 KΩ values and costs ~$19.51 ea/50. It is available from a number of distributors.

Fig. 2: The Vishay Precision group Z-Series resistor

VPG also offers axial lead wirewound resistors with excellent tolerances, like the MR106500R00TAE66 500 Ω, 250 MW part with 0.01% tolerance and 2 ppm/°C drift. But these cost $45 ea/50.

SUSUMU International has the RG and URG surface mount series in 0402 to 1206 sizes. They have 0.01% precision with 5 ppm/°C TCR. The 805 and 1206 versions have an optional 2 ppm/°C specification. The RG2012L-152-L-T05 1/10 W 1.5 KΩ part has the 2 ppm spec and is available for only $2.52 ea/100.

Caddock makes the USF 200 series of 0.33 W resistors with values from 50 Ω to 10 MΩ. These are larger (0.75 x 0.375-inch) through-hole devices with a 2 ppm TCR from -40° to +85°C and a tolerance of 0.01%. Matched pairs are also available. They are constructed with two selected USF 300 Series resistors bonded back-to-back to achieve very low TCR performance. The resistors are to be connected in parallel on the circuit board. 

Fig. 3: The Caddock through-hole precision resistor

RCD Components offers their BLU series of precision SMT resistors with 0.01% tolerance and a TCR of 5 ppm/°C. In a 0805 size, this accuracy is available in 50 Ω to 16 KΩ. Only the ±10 ppm version seems to be readily available. An example part number of BLU08051002TT10 would be for a 1 KΩ 10 ppm/°C. Prices seem to vary greatly for this part.

RCD also makes precision wirewound in SMT and through-hole with 0.005% tolerance available.