A1642LK-I1-T View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
A1642LK-I1-T
Allegro MicroSystems
'A1642LK-I1-T' PDF : 13 Pages View PDF
A1642LK
Two-Wire True Zero-Speed Miniature Differential Peak-Detecting Sensor with Continuous Calibration
SENSOR OPERATION
Each operating mode is described in detail below.
Power-On
When power (VCC > VCC(Min)) is applied to the device, a short
period of time is required to power the various portions of the
IC. During this period, the A1642 powers-on in the high current
state, ICC(High). After power-on, there are conditions that could
induce a change in the output state. Such an event could be
caused by thermal transients, but would require a static applied
magnetic field, proper signal polarity, and particular direction
and magnitude of internal signal drift.
Initial Offset Adjust
The sensor initially cancels the effects of chip, magnet, and
installation offsets. Once offsets have been cancelled, the digital
tracking DAC is ready to track the signal and provide output
switching. The period of time required for both Power-On and
Initial Offset Adjust is defined as the Power-On Time.
Calibration Mode
The calibration mode allows the sensor to automatically select
the proper signal gain and continue to adjust for offsets. The
AGC is active, and selects the optimal signal gain based on the
amplitude of the VPROC signal. Following each adjustment to
the AGC DAC, the Offset DAC is also adjusted to ensure the
internal analog signal is properly centered.
During this mode, the tracking DAC is active and output switch-
ing occurs, but the duty cycle is not guaranteed to be within
specification.
Running Mode
After the Initial Calibration period, CI, establishes a signal gain,
the device moves to Running mode. During Running mode, the
sensor tracks the input signal and gives an output edge for every
peak of the signal. AOA remains active to compensate for any
offset drift over time.
The A1642 incorporates a novel algorithm for adjusting the
signal gain during Running mode. This algorithm is designed
to optimize the VPROC signal amplitude in instances where the
magnetic signal “seen” during the calibration period is not repre-
sentative of the amplitude of the magnetic signal for the installed
sensor air gap (see figure 9).
1
Internal Differential
Signal, VPROC
2
3
4
BOP
BRP
5
BOP
BRP
Sensor Electrical
Output, IOUT
Figure 9: Operation of Running Mode Gain Adjust.
Position 1. The device is initially powered-on. Self-calibration occurs.
Position 2. Small amplitude oscillation of the target sends an erroneously small differential signal to the sensor. The ampli-
tude of VPROC is greater than the switching hysteresis (BOP and BRP), and the device output switches.
Position 3. The calibration period completes on the third rising output edge, and the device enters Running mode.
Position 4. True target rotation occurs and the correct magnetic signal is generated for the installation air gap. The estab-
lished signal gain is too large for the target’s rotational magnetic signal at the given air gap.
Position 5. Running Mode Calibration corrects the signal gain to an optimal level for the installation air gap.
A1642LK-DS
Allegro MicroSystems, Inc.
11
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
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