ATS660LSB
TRUE ZERO-SPEED,
HALL-EFFECT ADAPTIVE
GEAR-TOOTH SENSOR
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.
ꢀ immunity to magnetic overshoot — the air-gap
independent hysteresis minimizes the impact of overshoot
on the switching of device output,
ꢀ response to surface defects in the gear — the gain-
adjust circuitry reduces the effect of minor gear anomalies
that would normally causes false switching,
ꢀ 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,
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
ꢀ temperature drift* — changes in temperature do not
greatly affect this device due to the stable amplifier design
and the offset rejection circuitry,
ꢀ 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,
ꢀ immunity to gear run out — the differential-sensor
configuration eliminates the base-line variations caused by
gear run out, and
ꢀ 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:
ꢀ tooth width (T) > 2 mm;
ꢀ valley width (pC - T) > 2 mm;
ꢀ valley depth (ht) > 2 mm;
ꢀ gear thickness (F) > 3 mm; and the
ꢀ 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.
ꢀ dual edge detection — because this device references
the positive and negative peaks of the signal, dual edge
detection is guaranteed,
* Target must be rotating for proper update algorithim
operation.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
8
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