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PDF A3291 Data sheet ( Hoja de datos )
| Número de pieza | A3291 | |
| Descripción | Precision Hall-Effect Latches | |
| Fabricantes | Allegro | |
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A3290 and A3291
Chopper-Stabilized, Precision Hall-Effect Latches for
Consumer and Industrial Applications
FEATURES AND BENEFITS
• Symmetrical switchpoints
• Resistant to physical stress
• Superior temperature stability
• Output short-circuit protection
• Operation from unregulated supply
• Reverse battery protection
• Solid-state reliability
• Small package size
Packages:
3-Pin SOT23W
(suffix LH)
3-Pin SIP (suffix UA)
Not to scale
DESCRIPTION
The A3290 and A3291 Hall-effect latches are extremely
temperature-stable and stress-resistant sensor ICs, especially
suited for operation over extended temperature ranges (up
to 125°C). Superior high-temperature performance is made
possible through dynamic offset cancellation, which reduces
the residual offset voltage normally caused by device package
overmolding, temperature dependencies, and thermal stress.The
two devices are identical except for their magnetic switchpoints.
They are not intended for automotive applications.
Both devices include, on a single silicon chip, a voltage regulator,
a Hall voltage generator, a small-signal amplifier, chopper
stabilization, a Schmitt trigger, and a short-circuit protected
open-drain output to sink up to 25 mA.Asouth polarity magnetic
field of sufficient strength is required to turn the output on. A
north polarity field of sufficient strength is necessary to turn
the output off. An onboard regulator permits operation with
supply voltages in the range of 3 to 24 V.
Two package styles provide a magnetically optimized package
for most applications: type LH is a miniature SOT23W low-
profile surface-mount package, and type UA is a three-pin
ultramini SIP for through-hole mounting. Both packages are
lead (Pb) free with 100% matte-tin leadframe plating.
(A3290)
VCC
(A3291)
Amp
Regulator
Low-Pass
Filter
Control
Current Limit
OUT
1Ω
GND
A3290-DS, Rev. 15
Functional Block Diagram
1 page  
A3290 and
A3291
Chopper-Stabilized, Precision Hall-Effect Latches
for Consumer and Industrial Applications
FUNCTIONAL DESCRIPTION
Chopper-Stabilized Technique
The Hall element can be considered as a resistor array similar
to a Wheatstone bridge. A basic circuit is shown in Figure 1,
demonstrating the effect of the magnetic field flux density (B)
impinging on the Hall element. When using Hall-effect tech-
nology, a limiting factor for switchpoint accuracy is the small
signal voltage (VHALL) developed across the Hall element. This
voltage is disproportionally small relative to the offset that can
be produced at the output of the Hall device, caused by device
overmolding, temperature dependencies, and thermal stress.
A large portion of the offset is a result of the mismatching of
these resistors. The A3290 and A3291 use a proprietary dynamic
offset cancellation technique, with an internal high-frequency
clock, to reduce the residual offset. The chopper-stabilizing tech-
nique cancels the mismatching of the resistor circuit by changing
the direction of the current flowing through the Hall element
(refer to Figure 2). To do so, CMOS switches and Hall voltage
measurement taps are used, while maintaining VHALL signal that
is induced by the external magnetic flux.
The signal is then captured by a sample-and-hold circuit and fur-
ther 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
+V CC B
+VHALL
–V HALL
Figure 1: Hall Element, Basic Circuit Operation
Regulator
recoverability after temperature cycling. This technique will also
slightly degrade the device output repeatability. A relatively high
sampling frequency is used in order to process faster signals.
More detailed descriptions of the circuit operation can be found
on the Allegro website, including: Technical Paper STP 97-10,
Monolithic Magnetic Hall Sensing Using Dynamic Quadrature
Offset Cancellation, and Technical Paper STP 99-1, Chopper-
Stabilized Amplifiers with a Track-and-Hold Signal Demodula-
tor.
Operation
The outputs of the A3290 and A3291 switch low (turn on) when
a magnetic field perpendicular to the Hall element transitions
through and exceeds the Operate Point threshold (BOP). This
is illustrated in Figure 3. After turn-on, the output is capable of
sinking 25 mA, and the output voltage reaches VOUT(SAT).
Note that these devices latch; that is, after a south (+) polarity
magnetic field of sufficient strength impinging on the branded
face of the device turns on the device, the device remains on
until the magnetic field is reduced below the Release Point
threshold (BRP ). At that transition, the device output goes high
(turns off). The difference in the magnetic operate and release
points is the hysteresis (BHYS) of the device. This built-in hyster-
esis allows clean switching of the output, even in the presence
of external mechanical vibration and electrical noise.
When the devices are powered on, if the ambient magnetic field
has an intensity that is between BOP and BRP , the initial output
state is indeterminate. The first time that the level of B either
rises through BOP , or falls through BRP , however, the correct
output state is obtained.
Hysteresis of ∆VOUT
Switching Due to ∆B
V+
VOUT(off)
Amp
Low-
Pass
Filter
Figure 2: Chopper Stabilization Circuit (Dynamic
Quadrature Offset Cancellation)
VOUT(on)(sat)
B+
BHYS
Figure 3: Output Voltage Responds to Sensed Mag-
netic Flux Density
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet A3291.PDF ] | |
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