a3210ex Allegro MicroSystems, Inc., a3210ex Datasheet - Page 6

• Manufacturer Part Number: a3210ex
• Description: Micropower, Ultra-sensitive Hall-effect Switches
• Manufacturer: Allegro MicroSystems, Inc.

6
Low Average Power. Internal timing circuitry activates the
device for 60 µs and deactivates it for the remainder of the
period (480 µs for the A3209Ex and 60 ms for the A3210Ex).
A short "awake" time allows for stabilization prior to the
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.
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
cancellation 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 dependen-
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. This technique will also slightly degrade the device
output repeatability. A relatively high sampling frequency is
used in order that faster signals can be processed.
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.
I
I
DD(DIS)
DD(EN)
3209
MICROPOWER,
ULTRA-SENSITIVE
HALL-EFFECT SWITCHES
More detailed descriptions of the circuit operation can be
0
AND
SAMPLE &
OUTPUT LATCHED
60 µs - "AWAKE"
3210
"SLEEP"
PERIOD
FUNCTIONAL DESCRIPTION
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
Dwg. WH-017-1
Operation. The output of this device switches low (turns on)
when a magnetic field perpendicular to the Hall element exceeds
the operate point B
output is capable of sinking up to 1 mA and the output voltage
is V
release point B
switches high (turns off). The difference in the magnetic
operate and release points is the hysteresis (B
This built-in hysteresis allows clean switching of the output
even in the presence of external mechanical vibration and
electrical noise.
than zero (algebraic convention) and -50 G is less than +10 G.
OUT(ON)
As used here, negative flux densities are defined as less
. When the magnetic field is reduced below the
+V
RPS
+V
B
(or increased above B
OPS
X
(or is less than B
Dwg. AH-011-2
HALL
VOLTAGE
OPN
RPN
—
+
). After turn-on, the
), the device output
hys
) of the device.
Dwg. EH-012-1