ATS612LSB datasheet(14/16 Pages) ALLEGRO

14 / 16 page

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

ATS612LSB

DYNAMIC, SELF-CALIBRATING, PEAK-DETECTING,

DIFFERENTIAL HALL-EFFECT GEAR-TOOTH SENSOR

Operation From a Regulated Power Supply. These

devices require minimal protection circuitry during opera-

tion from a low-voltage regulated line. The on-chip voltage

regulator provides immunity to power supply variations

between 3.6V and 24V. However, even while operating

from a regulated line, some supply and output filtering is

required to provide immunity to coupled and injected noise

on the supply line. A basic RC low-pass circuit (R1C1) on

the supply line and an optional output capacitor (C2) is

recommended for operation in noisy environments.

Because the device has an open-collector output, an

output pull-up resistor (RL) must be included either at the

sensor output (pin 2) or by the signal processor input.

sufficiently high reverse breakdown capabilities so as to

withstand the most negative transient. The current-limiting

resistor (RZ) and the Zener diode should be sized for

power dissipation requirements.

Capacitor Requirements. The choice of the capacitor at

pin 3 (C3) defines the minimum operating speed of the

target. This capacitor (0.1

µF minimum) is required to

stabilize the internal amplifiers as well as to eliminate the

signal offsets. Typically, a 0.22

µF low-leakage ceramic

capacitor is recommended. Values greater than 0.47

µF

should not be used as this may cause high-speed perfor-

mance degradation.

Capacitor leakage current at pin 3 will cause degra-

dation in the low-speed performance of the device. Ex-

cess capacitor leakage can result in the sensor changing

output state without movement of the gear tooth being

sensed. In addition to the capacitor leakage, it is ex-

tremely important to minimize the leakage at the PC board

and between the pins of the sensor. Up to 50nA of

external leakage can be tolerated at the capacitor pin node

to ground. Choice of low-leakage-current potting com-

pounds and the use of clean PC board techniques are

extremely important.

Additional applications Information on gear-tooth

and other Hall-effect sensors is provided in the

Allegro

Integrated and Discrete Semiconductors Data Book or

Application Note 27701.

Vcc

Dwg. EH-008A

Ω

0.033

µF

0.22

µF

100 pF

OUTPUT

SUPPLY

0.033

µF

2.5 k

Ω

6.8 V

C 2

R 1

R Z

C S

Dwg. EH-008-1A

Vcc

Ω

R L

0.033

µF

0.22

µF

100 pF

OUTPUT

SUPPLY

C 1

R 1

Operation From an Unregulated Power Supply. In

automotive applications, where the device receives its

power from an unregulated supply such as the battery, full

protection is generally required so that the device can

withstand the many supply-side transients. Specifications

for such transients vary between car manufacturers, and

protection-circuit design should be optimized for each

application. In the circuit below, a simple Zener-controlled

regulator is constructed using discrete components. The

RC low-pass filter on the supply line (R1C1) and a low-

value supply bypass capacitor (CS) can be included, if

necessary, so as to minimize susceptibility to EMI/RFI.

The npn transistor should be chosen with sufficiently high

forward breakdown voltage so as to withstand supply-side

transients. The series diode should be chosen with

APPLICATIONS INFORMATION — Continued

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