link to page 7 AD8468Data Sheet500mV OVERDRIVECROSSOVER BIAS POINT Rail-to-rail inputs of this type, in both op amps and comparators, INPUT VOLTAGE have a dual front-end design. Certain devices are active near the 10mV OVERDRIVE VCC rail and others are active near the VEE rail or ground. At some VN ± VOS predetermined point in the common-mode range, a crossover occurs. At this point, normally VCC/2, the direction of the bias current reverses, and there are changes in measured offset DISPERSION 0 voltages and currents. -01 3 Q OUTPUT 85 08 The AD8468 slightly elaborates on this scheme. Crossover Figure 10. Propagation Delay—Overdrive Dispersion points can be found at approximately 0.8 V and 1.6 V. MINIMUM INPUT SLEW RATE REQUIREMENTINPUT VOLTAGE1V/ns With the rated load capacitance and normal good PC board design practice, as discussed in the Optimizing Performance VN ± VOS10V/ns section, these comparators should be stable at any input slew rate with no hysteresis. Broadband noise from the input stage is observed in place of the violent chattering seen with most other high speed comparators. With additional capacitive loading or DISPERSION poor bypassing, oscillation may be encountered. These oscilla- 11 0 3- Q OUTPUT tions are due to the high gain bandwidth of the comparator in 85 08 Figure 11. Propagation Delay—Slew Rate Dispersion combination with feedback through parasitics in the package and PC board. In many applications, chattering is not harmful. Rev. A | Page 8 of 12 Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION REVISION HISTORY SPECIFICATIONS ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS APPLICATIONS INFORMATION POWER/GROUND LAYOUT AND BYPASSING TTL-/CMOS-COMPATIBLE OUTPUT STAGE OPTIMIZING PERFORMANCE COMPARATOR PROPAGATIONDELAY DISPERSION CROSSOVER BIAS POINT MINIMUM INPUT SLEW RATE REQUIREMENT TYPICAL APPLICATION CIRCUITS OUTLINE DIMENSIONS ORDERING GUIDE AUTOMOTIVE PRODUCTS