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ATS612LSB Datasheet(PDF) 9 Page - Allegro MicroSystems |
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ATS612LSB Datasheet(HTML) 9 Page - Allegro MicroSystems |
9 / 17 page 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 ATS660LSB TRUE ZERO-SPEED, HALL-EFFECT ADAPTIVE GEAR-TOOTH SENSOR 8 DEVICE DESCRIPTION — Continued In addition to the gain control circuitry, the device also has provisions to zero out chip, magnet, and installation offsets. This is accomplished using two D-to-A converters that capture the peak and valley of the signal and use them as a reference for the switching comparator. This allows the switch points to be precisely controlled independent of air gap or temperature. The two Hall transducers and the electronics are inte- grated on a single silicon substrate using a proprietary BiCMOS process. Solution advantages. The ATS660LSB true zero- speed detecting gear-tooth sensor uses a differential Hall- element configuration. This configuration is superior in most applications to a classical single-element GTS. The single-element configuration commonly used requires the detection of an extremely small signal (often <100 G) that is superimposed on an extremely large back biased field, often 1500 G to 3500 G. For most gear configurations, the back-biased field values change due to concentration effects, resulting in a varying baseline with air gap, with eccentricities, and with vibration. The differential con- figuration eliminates the effects of the back-biased field through subtraction and, hence, avoids the issues presented by the single Hall element. The signal-processing circuitry also greatly enhances the functionality of this device. Other advantages are s temperature drift* — changes in temperature do not greatly affect this device due to the stable amplifier design and the offset rejection circuitry, s timing accuracy/duty cycle variation due to air gap* — the accuracy variation caused by air-gap changes is minimized by the self-calibration circuitry. A two-to-three times improvement can be seen over conventional zero- crossing detectors, s dual edge detection — because this device references the positive and negative peaks of the signal, dual edge detection is guaranteed, s immunity to magnetic overshoot — the air-gap independent hysteresis minimizes the impact of overshoot on the switching of device output, s response to surface defects in the gear — the gain- adjust circuitry reduces the effect of minor gear anomalies that would normally causes false switching, s immunity to vibration and backlash — the gain-adjust circuitry keeps the hysteresis of the device roughly propor- tional to the peak-to-peak signal. This allows the device to have good immunity to vibration even when operating at close air gaps, s immunity to gear run out — the differential-sensor configuration eliminates the base-line variations caused by gear run out, and s use with stamped-gear configurations — the high- sensitivity switch points allow the use of stamped gears. The shallow mechanical slopes created by the stamping process create an acceptable magnetic gradient down to zero speed. The surface defects caused by stamping the gear are ignored through the use of gain control circuitry. Operation versus air-gap/tooth geometry. Operat- ing specifications are impacted by tooth size, valley size and depth, gear material, and gear thickness. In general, the following guidelines should be followed to achieve greater than 2 mm air gap from the face of unit: s tooth width (T) > 2 mm; s valley width (p C - T) > 2 mm; s valley depth (h t) > 2 mm; s gear thickness (F) > 3 mm; and the s gear material must be low-carbon steel. Signal duty cycle. For regular tooth geometry, precise duty cycle is maintained over the operating air-gap and temperature range due to an extremely good symmetry in the magnetic switch points of the device. For irregular tooth geometry, there will a small but noticeable change in pulse width versus air gap. * Target must be rotating for proper update algorithim operation. |
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