Two-Wire, Zero-Speed

Differential Gear Tooth Sensor IC

ATS684LSN

13

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 minimum operating

the state of the magnetic gradient from the target. This lockout

feature prevents false signals, caused by undervoltage conditions,

may not be within specification.

Power Supply Protection

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

lated power supply, transient protection must be added externally.

For applications using a regulated line, EMI/RFI protection may

still be required. Contact Allegro for information on the circuitry

needed for compliance with various EMC specifications.

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 specifica-

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

tude of the signal generated by the target. The gain is then auto-

matically adjusted. Figure 9 illustrates the effect of this feature.

Running Mode Gain Adjust

The ATS684 has a feature during Running mode to compensate

for dynamic air gap variation. If the system increases the mag-

netic input drastically, the device will gradually readjust the gain

downwards, allowing the chip to regain the optimum internal

electrical signal with the new, larger, magnetic signal.

Dynamic Offset Cancellation (DOC)

The offset circuitry when combined with AGC automatically

reduces the effects of chip, magnet, and installation offsets. This

circuitry is continuously active, including both Power-on mode

and Running mode, compensating for any offset drift (within

Allowable User-Induced Differential Offset). Continuous opera-

tion also allows it to compensate for offsets induced by tempera-

ture variations over time.

Running Mode Lockout

The ATS684 has a Running mode lockout feature to prevent

switching on small signals that are characteristic of vibration

signals. The internal logic of the chip evaluates small signal

amplitudes below a certain level to be vibration. In that event, the

output is blanked (locked-out) until the amplitude of the signal

returns to normal operating levels.

Watchdog

The ATS684 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.

The AGC function corrects for

variances in the air gap. Differences

in the air gap cause differences in the

magnetic field at the device, but AGC

prevents that from affecting device

performance, as shown in the lowest

panel.

Mechanical Profile

Internal Differential

Analog Signal

Response, with AGC

Internal Differential

Analog Signal

Response, without AGC

Ferrous Target

V+

V+

Figure 9: Automatic Gain Control (AGC).