A3211 ALLEGRO [Allegro MicroSystems], A3211 Datasheet - Page 7

• Manufacturer Part Number: A3211
• Description: Micropower, Ultra-sensitive Hall-effect Switches
• Manufacturer: ALLEGRO [Allegro MicroSystems]

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 sam pling 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.
I
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 de pen den cies, 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.
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DD(DIS)
DD(EN)
A3211
A3212
0
and
SAMPLE &
OUTPUT LATCHED
"AWAKE"
"SLEEP"
PERIOD
FUNCTIONAL DESCRIPTION
Dwg. WH-017-2
Micropower, Ultrasensitive
+V
X
+V
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
Hall Effect Switch
B
Dwg. AH-011-2
HALL
VOLTAGE
Dwg. EH-012-1
—
+
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