A3295 Datasheet

A3295
Chopper Stabilized, Precision Hall Effect Switch for
Consumer and Industrial Applications
FEATURES AND BENEFITS
•
•
•
•
•
•
•
DESCRIPTION
Resistant to physical stress
Superior temperature stability
Output short-circuit protection
Operation from unregulated supply
Reverse battery protection
Solid-state reliability
Small package size
The A3295 Hall effect switch is an extremely temperaturestable 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.
Packages:
3-Pin SOT23W (suffix LH)
3-Pin SIP (suffix UA)
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. A south 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 lowprofile 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.
Not to scale
VCC
Amp
Sample and Hold
Dynamic Offset
Cancellation
Regulator
OUT
Low-Pass
Filter
Control
Current Limit
1Ω
GND
Functional Block Diagram
A3295-DS, Rev. 11
Chopper Stabilized, Precision Hall Effect Switch
for Consumer and Industrial Applications
A3295
SPECIFICATIONS
Selection Guide
Magnetic Switchpoints2
Part Number
Packing1
Package Type
A3295KLHLT-T
3000 pieces per 7-in. reel
Surface mount SOT23W
A3295KLHLX-T
10000 pieces per 13-in. reel
Surface mount SOT23W
A3295KUA-T
500 pieces per bulk bag
Through hole ultramini SIP
Operate,
BOP (G)
Release, BRP
(G)
75 max.
5 min.
1Contact Allegro
21
for additional packing options.
G (gauss) = 0.1 mT (millitesla).
Absolute Maximum Ratings
Rating
Units
Supply Voltage
Characteristic
Symbol
VCC
Notes
26.5
V
Reverse Battery Voltage
VRCC
–30
V
Output Off Voltage
VOUT
26
V
Continuous Output Current
IOUT
25
mA
Reverse Output Current
IROUT
–50
mA
Device provides internal current limiting to help protect itself
from output short circuits
Magnetic Flux Density
B
Operating Ambient Temperature
TA
Maximum Junction Temperature
TJ(max)
165
ºC
Tstg
–65 to 170
ºC
Storage Temperature
Range K
Terminal List
3
Name
PTCT
PTCT
1
2
1
Package LH,
3-Pin SOT23W Pin-out
Diagram
2
VCC
OUT
GND
LH
1
2
3
Number
UA
1
3
2
Unlimited
G
–40 to 125
ºC
Function
Power supply
Output
Ground
3
Package UA,
3-Pin SIP Pin-out
Diagram
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
Chopper Stabilized, Precision Hall Effect Switch
for Consumer and Industrial Applications
A3295
ELECTRICAL CHARACTERISTICS over operating temperature range, unless otherwise noted
Characteristic
Supply Voltage
Range2
Output Leakage Current
Output Saturation Voltage
Symbol
Test Conditions
Min.
Typ.1
Max
Units
VCC
Operating, TJ < 165°C
3.0
–
24
V
IOFF
VOUT = 24 V, B < BRP
–
–
10
µA
VOUT(SAT)
IOUT = 20 mA, B > BOP
–
185
500
mV
Output Current Limit
ION
B > BOP
30
–
60
mA
Power-On Time
tPO
VCC > 4.2 V
–
–
50
µs
Chopping Frequency
fC
–
800
–
kHz
Output Rise Time
tR
RLOAD = 820 Ω, CLOAD = 20 pF
–
0.2
2.0
µs
Output Fall Time
tF
RLOAD = 820 Ω, CLOAD = 20 pF
–
0.1
2.0
µs
B < BRP , VCC = 12 V
–
3.0
8.0
mA
B > BOP , VCC = 12 V
–
4.0
8.0
mA
VRCC = –30 V
–
–
–5.0
mA
ICC = 15 mA, TA = 25°C
28
–
–
V
–
50
–
Ω
Min.
Typ.
Max.
Units
–
–
75
G
5
–
–
G
–
–
70
G
Supply Current
ICC
Reverse Battery Current
IRCC
Zener Voltage
VZ + VD
Zener Impedance
ZZ + ZD
ICC = 15 mA, TA = 25°C
1Typical data at T = 25°C, 12 V.
A
2Maximum V
CC must be derated for power dissipation and junction temperature. See Application Information.
MAGNETIC CHARACTERISTICS over VCC range, unless otherwise noted
Characteristic
Operate Point
Symbol
Test Conditions
BOP
Release Point
BRP
Hysteresis
BHYS
BOP – BRP
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A3295
Chopper Stabilized, Precision Hall Effect Switch
for Consumer and Industrial Applications
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic
Symbol
Package Thermal Resistance
Test Conditions*
RθJA
Value
Units
Package LH, 1-layer PCB with copper limited to solder pads
228
ºC/W
Package LH, 2-layer PCB with 0.463 in.2 of copper area each side
connected by thermal vias
110
ºC/W
Package UA, 1-layer PCB with copper limited to solder pads
165
ºC/W
*Additional thermal information available on Allegro website.
Maximum Allowable VCC (V)
Power Derating Curve
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
VCC(max)
2-layer PCB, Package LH
(RθJA = 110 ºC/W)
1-layer PCB, Package UA
(RθJA = 165 ºC/W)
1-layer PCB, Package LH
(RθJA = 228 ºC/W)
20
40
60
80
100
120
VCC(min)
140
160
180
Temperature (ºC)
Power Dissipation, PD (m W)
Power Dissipation versus Ambient Temperature
1900
1800
1700
1600
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
2l
(R aye
rP
θJ
C
A =
11 B, P
0 º ac
1-la
C/ ka
W
(R yer PC
) ge L
θJA =
B
H
165 , Pac
ºC/ kage
W)
UA
1-lay
er P
(R
CB,
θJA =
228 Packag
ºC/W
e LH
)
20
40
60
80
100
120
Temperature (°C)
140
160
180
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
Chopper Stabilized, Precision Hall Effect Switch
for Consumer and Industrial Applications
A3295
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 technology, 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 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 further 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, ChopperStabilized Amplifiers with a Track-and-Hold Signal Demodulator.
Operation
The output of the A3295 switches low (turns 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 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 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
V+
Hysteresis of ∆VOUT
Switching Due to ∆B
VOUT(off)
Switch to High
VOUT
VOUT(on)(sat)
BOP
BRP
LowPass
Filter
Switch to Low
Amp
Sample and Hold
Regulator
B+
BHYS
Figure 2: Chopper Stabilization Circuit (Dynamic
Quadrature Offset Cancellation)
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
A3295
Chopper Stabilized, Precision Hall Effect Switch
for Consumer and Industrial Applications
When the device is 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.
APPLICATION INFORMATION
It is strongly recommended that an external bypass capacitor be
connected (in close proximity to the Hall element) between the
supply and ground of the device to reduce both external noise
and noise generated by the chopper-stabilization technique. This
configuration is shown in figure 4.
The simplest form of magnet that will operate these devices is a
ring magnet. Other methods of operation, such as linear magnets,
are possible.
The device must be operated below the maximum junction
temperature of the device, TJ(max). Under certain combinations of
peak conditions, reliable operation may require derating supplied
power or improving the heat dissipation properties of the application. The Package Thermal Resistance, RθJA, is a figure of merit
summarizing the ability of the application and the device to dissi-
pate heat from the junction (die), through all paths to the ambient
air. Its primary component is the Effective Thermal Conductivity,
K, of the printed circuit board, including adjacent devices and
traces. Radiation from the die through the device case, RθJC, is
relatively small component of RθJA. Ambient air temperature,
TA, and air motion are significant external factors, damped by
overmolding. Sample power dissipation results are given in the
Thermal Characteristics section. Additional thermal data is also
available on the Allegro website.
Extensive applications information for Hall-effect devices is
available in: Hall-Effect IC Applications Guide, Application Note
27701 and Guidelines for Designing Subassemblies Using HallEffect Devices, Application Note 27703.1
VCC
A3295
VCC
0.1 uF
VOUT
GND
Figure 4: Typical Basic Application Circuit
A bypass capacitor is highly recommended.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
Chopper Stabilized, Precision Hall Effect Switch
for Consumer and Industrial Applications
A3295
CUSTOMER PACKAGE DRAWINGS
For Reference Only – Not for Tooling Use
(Reference DWG-2840)
Dimensions in millimeters – NOT TO SCALE
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
+0.12
2.98 –0.08
D
1.49
4° ±4°
A
3
+0.020
0.180 –0.053
0.96
D
+0.19
1.91 –0.06
+0.10
2.90 –0.20
2.40
0.70
D
0.25 MIN
1.00
2
1
0.55 REF
0.25 BSC
0.95
Seating Plane
Branded Face
Gauge Plane
B
PCB Layout Reference View
8X 10°
REF
1.00 ±0.13
A1101, A1102,
A1103, A1104,
and A1106
NNT
+0.10
0.05 –0.05
0.95 BSC
0.40 ±0.10
N = Last three digits of device part number
T = Temperature Code (Letter)
A Active Area Depth, 0.28 mm
B Reference land pattern layout; all pads a minimum of 0.20 mm from all adjacent pads;
adjust as necessary to meet application process requirements and PCB layout tolerances
C Branding scale and appearance at supplier discretion
A1101, A1102,
A1103, and
A1104, only
NNN
D Hall elements, not to scale
N = Last three digits of device part number
C
Standard Branding Reference View
Figure 5: Package LH, 3-Pin SOT23W
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
Chopper Stabilized, Precision Hall Effect Switch
for Consumer and Industrial Applications
A3295
For Reference Only – Not for Tooling Use
(Reference DWG-9049)
Dimensions in millimeters – NOT TO SCALE
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
45°
B
4.09
+0.08
–0.05
1.52 ±0.05
E
2.04
C
2 X 10°
1.44 E
3.02
E
Mold Ejector
Pin Indent
+0.08
–0.05
45°
Branded
Face
2.16 MAX
0.51 REF
A
1
2
0.79 REF
3
0.43
+0.05
–0.07
0.41
+0.03
–0.06
1.27 NOM
NNT
15.75 ±0.25
1
D
Standard Branding Reference View
= Supplier emblem
N = Last three digits of device part number
T = Temperature code
A
Dambar removal protrusion (6X)
B
Gate and tie bar burr area
C
Active Area Depth, 0.50 mm REF
D
Branding scale and appearance at supplier discretion
E
Hall element, not to scale
Figure 6: Package UA, 3-Pin SIP
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
A3295
Chopper Stabilized, Precision Hall Effect Switch
for Consumer and Industrial Applications
Revision History
Revision
Revision Date
9
November 11, 2012
10
January 2, 2015
11
July 13, 2015
Description of Revision
Conform Description
Added LX option to Selection Guide
Corrected LH package Active Area Depth value
Copyright ©2005-2015, Allegro MicroSystems, LLC
Allegro MicroSystems, LLC reserves the right to make, from time to time, such departures from the detail specifications as may be required to
permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that
the information being relied upon is current.
Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, LLC assumes no responsibility for its
use; nor for any infringement of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
Similar pages