Dynamic, Self-Calibrating, Threshold-Detecting, Differential

Speed and Direction Hall-Effect Gear Tooth Sensor IC

ATS657

11

Allegro MicroSystems, Inc.

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 volt-

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

lockout feature prevents false signals, caused by undervoltage

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. Refer to

figure 7 for an example of a basic application circuit.

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. The two differential channels have their gain set

independent of each other, so both channels may or may not have

the same gain setting.

Automatic Offset Adjust (AOA)

The AOA circuitry, when combined with AGC, automatically

compensates for the effects of chip, magnet, and installation

offsets. (For capability, see Allowable User Induced Differential

Offset, in the Electrical Characteristics table.) This circuitry is

continuously active, including both during Power-On mode and

Running mode, compensating for offset drift. Continuous opera-

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

ture variations over time. Similar to AGC, the AOA is set inde-

pendently for each channel, so the offset adjust is set per channel,

based on the offset characteristics of that specific channel.

Figure 8. Automatic Gain Control (AGC). 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.

Figure 7. Typical application circuit

Mechanical Profile

Internal Differential Signal

Response, without AGC

Internal Differential Signal

Response, with AGC

Ferrous Target

V+

V+

2

ATS657

1

3

4

0.01 F (optional)

100

R

L

C

L

C

BYPASS

V

CC