Issue link: https://resources.mouser.com/i/1442772
choosing high-value pull-up resistors where possible, or using load switches to disable entire sub-circuits via load switches when they are not needed. Also, components with low rail voltages usually offer low operating and quiescent currents, but this may compromise some other performance parameters. Using low voltages may be a challenge for analog circuits as these signals are by their nature sensitive to noise; low operating voltages often result in reduced signal-to-noise ratio (SNR) and thus require additional attention to both internal and external noise sources to minimize the impact. Further, modeling of the circuit performance at nominal-condition operation, as well as with temperature-related drift, maximum/minimum performance specifications, and tolerance of passive components is critical to design reliability and consistency. So Many Very Good Options The ideal op-amp or comparator with perfect performance specifications and requiring no power (other than what is being delivering to the load) doesn't exist. But many of today's devices come quite close, especially in the power area, with microamp active-mode current requirements as well as microamp and even nanoamp quiescent current ratings, as four examples demonstrate. The LPV801 (single channel) and LPV802 (dual channel) nanopower CMOS op-amps are designed for long run-time applications that are powered by small batteries or even energy harvesting, such as carbon dioxide (CO) and oxygen (O2) gas detectors, passive infrared (PIR) motion detectors Figure 5, and ionization smoke alarms. They operate from a single supply down to 1.6V with rail-to-rail output that swings to within 3.5mV of the supply rail with a 100kΩ load. Figure 5: The LPV802 dual op-amp is well-suited for long-life battery operation in applications such as the widely used PIR detector. (Source: Texas Instruments) However, those specifications don't tell the whole story, which includes the fact that their ultralow quiescent current of just 320nA/channel along with 8kHz of bandwidth—more than adequate for these applications— really stands out. Further, this quiescent current is fairly constant across the entire operating temperature range at a given supply voltage, Figure 6; this eases design-in worst-case calculations and simulation. Figure 6: While the quiescent current of the LPV801 op-amp increases with increasing temperature, it remains fairly constant across the entire supply-voltage range, which eases design analysis and corner case concerns. (Source: Texas Instruments) Some applications need an instrumentation amplifier, a specialized configuration of three op-amps that provides unique attributes with respect to gain, gain setting, bandwidth, stability, and common mode rejection. The INA828, Figure 7, features 50μV maximum offset, gain drift of 5ppm/°C (at gain G = 1) and 50ppm/°C (G > 1), extremely low noise of 7nV/√Hz, and wide bandwidth of 2MHz (G = 1) and 260kHz (G = 100). In addition, its maximum quiescent current is just 650μA at 25°C, rising to just 850μA at 125°C. It can be used in single-supply designs (5V) as well as those with dual supplies up to ±18V. Figure 7: In instrumentation, amplifiers such as the INA828 greatly minimize many sensor-interface concerns due to its ease of gain setting, high common mode rejection, and overall performance stability. (Source: Texas Instruments) 14