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PDF A3295 Data sheet ( Hoja de datos )
| Número de pieza | A3295 | |
| Descripción | Precision Hall Effect Switch | |
| Fabricantes | Allegro | |
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A3295
Chopper Stabilized, Precision Hall Effect Switch for
Consumer and Industrial Applications
FEATURES AND BENEFITS
• 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 A3295 Hall effect switch is an extremely temperature-
stable and stress-resistant sensor IC unipolar switch, 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 device is not intended for automotive applications.
The device includes, 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.
An onboard regulator permits operation with supply voltages
in the range of 3 to 24 volts.
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-lead
ultramini SIP for through-hole mounting. Both packages are
lead (Pb) free, with 100% matte tin plated leadframes.
VCC
A3295-DS, Rev. 11
Amp
Regulator
Low-Pass
Filter
Control
Current Limit
OUT
1Ω
GND
Functional Block Diagram
1 page  
A3295
Chopper Stabilized, Precision Hall Effect Switch
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 A3295 uses a proprietary dynamic offset
cancellation technique, with an internal high-frequency clock, to
reduce the residual offset, see figure 2. The chopper-stabilizing
technique cancels the mismatching of the resistor circuit by
changing the direction of the current flowing through the Hall
element. To do so, CMOS switches and Hall voltage measure-
ment 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
+V CC B
+VHALL
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 to process faster signals.
More detailed descriptions of the circuit operation can be found
on the Allegro Web site, 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 output of the A3295 switches low (turns on) when a mag-
netic field perpendicular to the Hall element transitions through
and exceeds the Operate Point threshold, BOP. This is illus-
trated in figure 3. After turn-on, the output is capable of sinking
25 mA, and the output voltage reaches VOUT(SAT).
Note that 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 transi-
tion, 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 hysteresis allows clean switching of
the output, even in the presence of external mechanical vibration
and electrical noise.
–V HALL
Figure 1: Hall Element, Basic Circuit Operation
Regulator
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 Magnetic 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 9 Páginas | |
| PDF Descargar | [ Datasheet A3295.PDF ] | |
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