AN854 Datasheet, PDF (2/3 Pages) Silicon Laboratories – VERSATILE BUFFERED REFERENCE IC

AN854
The nano-power reference in the TS12011 is unbuffered, a design trade-off taken to absolutely minimize the supply
current drain at all costs. You can only draw 100 nA from it, according to the data sheet specification. That is
acceptable if the reference is being used to set a comparator threshold or op-amp virtual ground level, but, if more
drive is needed, buffering is required. When dividing the reference output with resistors, lower values are generally
better from a noise and leakage standpoint, but care should be taken not to overload it. In Figure 1B, the total
divider series resistance must be 5.8 M or greater (0.58 V/100 nA). The TS12011 op amp has tighter offset
current specs than input bias current specs, so it usually makes sense to add a series resistor at the other input to
compensate for the high values used in the divider.
These basic reference circuits are a good starting point for all sorts of designs. Accuracy for Figure 1A is ±4.8%
including temp drift, VOS, IOS, and 1% resistor tolerances, which is good enough for building a wake-up detector,
timer, or power converter. The relatively high open-loop gain of the op amp keeps the load regulation characteristic
flat up to 1 mA. Supply current for either circuit is less than 2 µA. The extra latching comparator is a bonus, shown
employed as a voltage detector with 0.3 V trip threshold in Figure 1B.
Load Regulation
Circuit of Figure A, VDD = 1V
680
660
640
620
600
580
1
10
100
1000
ILOAD (uA)
10000
Figure 2. 0.666 V VREF Load Regulation
For additional information, please see the TS12011 data sheet.
2
Rev. 1.0