115 Northeast Cutoff, Box 15036

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

ATS660LSB

TRUE ZERO-SPEED,

HALL-EFFECT ADAPTIVE

GEAR-TOOTH SENSOR

10

APPLICATIONS INFORMATION — Continued

Operation from unregulated supply

Operation from regulated supply

Operation from a regulated power supply. These

devices require minimal protection circuitry during

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

voltage regulator provides immunity to power supply

variations between 4.5 V and 26.5 V. 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.

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 shown, a standard protection circuit is

constructed using discrete components. The Zener diode

is used to provide over-voltage protection against load

dumps greater than about 40 V; for load dumps less than

about 40 V, the internal Zener is sufficient. The series

resistor (R

1

) provides current limiting and with the capaci-

tor (C

1

) noise filtering. The Zener diode and current-

limiting resistor should be sized for power dissipation

requirements. The series diode protects the external Zener

diode against reverse battery and provides protection

against transients greater than -24 V; it must be rated to

withstand the most negative transient. In many transmis-

sion applications there is already a Zener diode in the

TCU, and the diode and external Zener are not necessary.

3

X

X

+

-

12

4

Vcc

Dwg. EH-008-6

RL

100 pF

C 2

OUTPUT

SUPPLY

C1

R 1

3

X

X

Dwg. EH-008-7

+

-

12

4

Vcc

20

Ω

R L

0.1

µF

100 pF

C2

OUTPUT

SUPPLY

C 1

R 1