TABLE OF CONTENTS As discussed in Chapter 14, the XFET is an outstanding voltage reference with many excellent features, including low cost. Most noticeable are its ultra-low noise level, a very low initial accuracy ( 0.05%, B-grade devices), low quiescent current (less than 800 ?A), a very flat 3 ppm/ C tempco, and a wider operating temperature range ( automotive, -40 C to +125 C), than most bandgaps or buried-zener types. Its tempco is flat and linear compared to either the bandgap or buried-zener, and its long-term drift is better than most other types of reference. Because its tempco is inherently lower than most bandgap references, much less compensation is required. Because less resistor noise (used for compensation) is involved, as well as using inherently low-noise JFETs at its reference core, this all helps the device have a significantly lower overall noise level. For example, the noise level for an ADR431 (2.5-volt) XFET is given as less than 4 ?V pk-pk (at 0.1 Hz to 10 Hz) typical, whereas the noise density at 1 KHz is typically 60nV/ ?Hz both excellent characteristics. The long-term stability of the device is typically 40 ppm/1000 hours, which is also impressive.
The output of a typical XFET uses a buffer amplifier, which provides a source capability of 30 mA, a sink capability of 20 mA, and an indefinite short-circuit current to ground of about 40 mA. This is significantly higher than most...
