Miniature, Two-Wire, True Zero Speed

Differential Peak-Detecting Sensor IC

ATS682LSH

12

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Device Operation

Power-On

device, a short period of time is required to activate the various

portions of the IC. During this period, the ATS682 powers-on in

tions that could induce a change in the output state. Such an event

could be caused by thermal transients, but it would also require a

static applied magnetic field, proper signal polarity, and particular

direction and magnitude of internal signal drift.

Initial Offset Adjust

The IC initially compensates for differ-

lation alignment. Once the effective differential magnetic offset

has 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 specification.

Calibration Mode

The calibration mode allows the IC to auto-

matically select the proper signal gain and continue to adjust for

DC differential magnetic offset. The AGC is active, and selects

signal. Following each adjustment to the AGC DAC, the Offset

DAC is also adjusted to ensure the internal analog signal is prop-

erly centered. During this mode, the tracking DAC is active and

output switching occurs, but the duty cycle is not guaranteed to

be within specification.

Running Mode

edges) establishes a signal gain, the device moves to Running

mode. During Running mode, the IC tracks the input signal and

continues to give an output edge for every peak of the signal.

AOA remains active to compensate for any offset drift over time.

The ATS682 also incorporates an algorithm for adjusting the

signal gain during Running mode. This algorithm is designed to

netic signal during the calibration period is not representative of

the amplitude of the magnetic signal for the installed application

air gap (see figure 9).

IC Electrical

Output, I

OUT

Internal Differential

Signal, V

PROC

1

2

3

4

5

Figure 9: Operation of Running Mode Gain Adjust.

Position 1. The device is initially powered-on. Self-calibration occurs.

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 established signal gain is too large for

the rotational magnetic signal of the target, at the given air gap.

Position 5. Running mode calibration corrects the signal gain to an optimal level for the installation air gap.