A3211EELLT-T Просмотр технического описания (PDF) - Allegro MicroSystems

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производитель

A3211EELLT-T

Micropower, Ultra-sensitive Hall-ef fect Switches

Allegro MicroSystems 

A3211 and

A3212

Micropower, Ultrasensitive

Hall Effect Switch

FUNCTIONAL DESCRIPTION

Low Average Power. Internal timing circuitry activates the

sensor for 45 μs and deactivates it for the remainder of the pe-

riod (45 ms). A short "awake" time allows for stabilization prior

to the sensor sampling and data latching on the falling edge of

the timing pulse. The output during the "sleep" time is latched in

the last sampled state. The supply current is not affected by the

output state.

IDD(EN)

IDD(DIS)

0

"AWAKE"

PERIOD

"SLEEP"

SAMPLE &

OUTPUT LATCHED

Dwg. WH-017-2

Chopper-Stabilized Technique. The Hall element can be

considered as a resistor array similar to a Wheatstone bridge. A

large portion of the offset is a result of the mismatching of these

resistors. These devices use a proprietary dynamic offset cancel-

lation technique, with an internal high-frequency clock to reduce

the residual offset voltage of the Hall element that is normally

caused by device overmolding, temperature dependencies, and

thermal stress. The chopper-stabilizing technique cancels the

mismatching of the resistor circuit by changing the direction of

the current flowing through the Hall plate using CMOS switches

and Hall voltage measurement taps, while maintaing the Hall-

voltage signal that is induced by the external magnetic flux. The

signal is then captured by a sample-and-hold circuit and further

processed using low-offset bipolar circuitry. This technique

produces devices that have an extremely stable quiescent Hall

output voltage, are immune to thermal stress, and have precise

recoverability after temperature cycling. A relatively high sam-

pling frequency is used for faster signal processing capability

can be processed.

More detailed descriptions of the circuit operation can be found

in: Technical Paper STP 97-10, Monolithic Magnetic Hall Sensor

Using Dynamic Quadrature Offset Cancellation and Technical

Paper STP 99-1, Chopper-Stabilized Amplifiers With A Track-

and-Hold Signal Demodulator.

B

+V

—

HALL

VOLTAGE

+

Dwg. AH-011-2

+V

X

Dwg. EH-012-1

Allegro MicroSystems, Inc.

7

115 Northeast Cutoff, Box 15036

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

www.allegromicro.com

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