True Zero-Speed High-Accuracy

Gear Tooth Sensor IC

ATS668LSM

10

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Undervoltage Lockout

When the supply voltage falls below the undervoltage lockout

plied. This lockout feature prevents false signals, caused by under-

voltage conditions, from propagating to the output of the IC.

Power Supply Protection

The device contains an on-chip regulator and can operate over a

EMC protection components virtually eliminating the need for

additional external passive components.

Automatic Gain Control (AGC)

This feature allows the device to operate with an optimal internal

electrical signal, regardless of the air gap (within the AG speci-

fication). At power-on, the device determines the peak-to-peak

amplitude of the signal generated by the target. The gain of the

IC is then automatically adjusted. Figure 8 illustrates the effect of

this feature.

Automatic Offset Adjust (AOA)

The AOA circuitry automatically compensates for the effects of

chip, magnet, and installation offsets. This circuitry is continu-

ously active, including during both power-on mode and running

mode, compensating for any offset drift (within the Allowable

User-Induced Differential Offset). Continuous operation also

allows it to compensate for offsets induced by temperature varia-

tions over time.

Running Mode Lockout

The ATS668 has a running mode lockout feature to prevent

switching in response to small signals that are characteristic

of vibration signals. The internal logic of the chip considers

small-signal amplitudes below a certain level to be vibration. The

output is held to the state prior to lockout until the amplitude of

the signal returns to normal operational levels.

Watchdog

The ATS668 employs a watchdog circuit to prevent extended loss

of output switching during sudden impulses and vibration in the

system. If the system changes the magnetic input drastically such

that target feature detection is terminated, the device will fully

reset itself, allowing the chip to recalibrate properly on the new

magnetic input signal.

Assembly Description

The ATS668 is integrally molded into a plastic body that has been

optimized for size, ease of assembly, and manufacturability. High

operating temperature materials are used in all aspects of con-

struction.

Mechanical Profile

Internal Differential

Analog Signal

Response, with AGC

Internal Differential

Analog Signal

Response, without AGC

Ferrous Target

V+

V+

Figure 8: Automatic Gain Control (AGC). The AGC

function corrects for variances in the air gap. Differ-

ences in the air gap cause differences in the magnetic

field at the device, but AGC prevents that from affect-

ing device performance, as shown in the lowest panel.