Variable-Reluctance Sensor Interface with Differential Input and Adaptive Peak Threshold

The MAX9924–MAX9927 variable reluctance (VR or magnetic coil) sensor interface devices are ideal for position and speed sensing for automotive crankshafts, camshafts, transmission shafts, etc. These devices integrate a precision amplifier and comparator with selectable adaptive peak threshold and zero-crossing circuit blocks that generate robust output pulses even in the presence of substantial system noise or extremely weak VR signals.

The MAX9926/MAX9927 are dual versions of the MAX9924/MAX9925, respectively. The MAX9924/MAX9926 combine matched resistors with a CMOS input precision operational amplifier to give high CMRR over a wide range of input frequencies and temperatures. The MAX9924/MAX9926 differential amplifiers provide a fixed gain of 1V/V. The MAX9925/MAX9927 make all three terminals of the internal operational amplifier available, allowing greater flexibility for gain. The MAX9926 also provides a direction output that is useful for quadrature-connected VR sensors that are used in certain high-performance engines. These devices interface with both new-generation differential VR sensors as well as legacy single-ended VR sensors.

The MAX9924/MAX9925 are available in the 10-pin µMAX® package, while the MAX9926/MAX9927 are available in the 16-pin QSOP package. All devices are specified over the -40°C to +125°C automotive temperature range.

Applications

* Camshaft VRS Interfaces * Crankshaft VRS Interfaces * Vehicle Speed VRS Interfaces

* Differential Input Stage Provides Enhanced Noise Immunity

* Precision Amplifier and Comparator Allows Small-Signal Detection

* User-Enabled Internal Adaptive Peak Threshold or Flexible External Threshold

* Zero-Crossing Detection Provides Accurate Phase Information