Understanding Smart Sensors - Nomads.usp

Getting Sensor Information Into the MCU 75B+GNDC10.2 µ F3 U1MC78L08ACPIOG2C20.2 µ FR7TrimNotes:R7 is nominally 39.2 k and seleceted for zero pressure V OUT = 0.5Vfor MPX2010 sensors R1 = 150 k and R4 = 61.9 Ohms1R51.33 k1%R339.2k1%3121R611 k1%XDCD1MPX2000 seriessensorU1B3 MC33272+ 12 −1R41001%5+6−8 7U2BMC33272R1 93.1 k 1%C2 0.001 µ FR27501%OUTFigure 4.2 Sensor-specific signal conditioning circuit.resistors. The MCU can increase this accuracy through software and avoid ananalog trim in the amplifier.4.2.2 SLEEPMODE Operational AmplifierIntegrated circuits designed to optimize performance may provide new solutionsfor smart sensors. For example, in battery-powered applications, the currentdrain and power consumption must be low to obtain optimum battery life.A bipolar operational amplifier has been designed that conserves power in portableand other low-power applications but can handle higher current drainfor improved performance [7]. The SLEEPMODE operational amplifier consumesonly 140 mA maximum (40 mA typical) with up to 5V when it is asleep. 1In the awake mode, it has a typical gain bandwidth product of 2.2 MHz and aCMRR of 90 dB and can drive 700 mA. The key elements of this IC are shownin Figure 4.3. In the sleep mode, the amplifier is active and waiting for an inputsignal from the sensor. When a signal is applied that sinks or sources 200 mA,the amplifier automatically switches to the awake mode for higher slew rate,increased gain bandwidth, and improved drive capability. The amplifier automaticallyreturns to sleep mode when the output current drops below thethreshold (90 mA). This unit swings within 100 mV (typical) of both rails.1. SLEEPMODE is a trademark of Semiconductor Components Industries, LLC (d.b.a. ONSemiconductor).