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1. Device Overview: ATS685LSH Gear Tooth Sensor

️· Function: A two-wire, zero-speed gear tooth sensor IC. It detects gear rotation and provides a digital output signal (current amplitude).
️· Two-Wire Sensing: Requires an external sense resistor (R SENSE) to convert the current output to a voltage signal for measurement. Can be placed on either the VCC or GND pins, affecting the output signal's polarity.
️· Power-On Behavior: The device initially powers on in a high current state (I CC(High)).
️· Initial Edge Detection: Self-calibrates using the first detected teeth, requiring a brief "calibration" period (CAL I) for optimal performance.

2. Output Signal & Polarity

️· Output Polarity States: The polarity of the output voltage (V SENSE) depends on the location of the sense resistor (R SENSE) relative to VCC and GND.
- Low-Side Sensing (GND pin side): V SENSE is in phase with I CC.
- High-Side Sensing (VCC pin side): V SENSE is inverted relative to I CC.
️· Automatic Gain Control (AGC): The device uses the first three rising edges (high peaks) after power-on to calibrate the AGC, which optimizes the sensitivity to gear tooth signals.

3. Key Features and Algorithms

️· Continuous Update Algorithm: This algorithm adapts to changes in the magnetic field induced by the target. This helps compensate for issues like:
- Eccentric mounting (target not perfectly centered)

- Out-of-round target shape
- Target position shifts
️· AGC Calibration: The duration of the AGC calibration period (CAL I) can vary depending on the target feature opposite the sensor IC upon power-on, and the target speed.

4. Operational Sequence (simplified)

1. Power-On: Device starts in high current state.
2. Initial Edge Detection: The device detects the first teeth and begins a calibration period.
3. AGC Calibration: The device uses the first few rising edges to calibrate the AGC.
4. Running Mode: The device operates in normal gear tooth sensing mode.



Essentially, the ATS685LSH is a robust sensor designed to work reliably even under less-than-ideal conditions (eccentric mounting, etc.) through its adaptive algorithms and automatic calibration.