Allegro A3245LLHLT-T Chopper-stabilized omnipolar hall-effect switch Datasheet

A3245
Chopper-Stabilized
Omnipolar Hall-Effect Switches
GND
Package LH, 3-pin Surface Mount
3
1
3
2
2
VCC
VOUT
1
1
2
3
VCC
GND
VOUT
Package UA, 3-pin SIP
1 2
3
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VCC .......................................... 28 V
Reverse-Supply Voltage, VRCC ........................ –18 V
Reverse-Supply Current, IRCC ........................–2 mA
Output Off Voltage, VOUT .................................. 28 V
Output Current, IOUTSINK ........... Internally Limited
Magnetic Flux Density, B .........................Unlimited
Operating Temperature
Ambient, TA, Range E.................. –40ºC to 85ºC
Ambient, TA, Range L................ –40ºC to 150ºC
Maximum Junction, TJ(MAX) ......................165ºC
Storage Temperature, TS .................. –65ºC to 170ºC
A3245-DS, Rev. 1
The A3245 integrated circuit is an omnipolar, ultrasensitive Hall-effect switch
with a digital output. This sensor has an integrated regulator permitting operation
to 24 V, making it the first omnipolar switch available for operation to 24 V. This
device is especially suited for operation over extended temperature ranges, up
to +150°C. Superior high-temperature performance is made possible through an
Allegro® patented dynamic offset cancellation, which reduces the residual offset
voltage normally caused by device overmolding, temperature excursions, and
thermal stress.
The A3245 Hall-effect switch includes the following on a single silicon chip:
voltage regulator, Hall-voltage generator, small-signal amplifier, chopper stabilization, Schmitt trigger, and a short circuit protected open-drain output. Advanced
BiCMOS wafer fabrication processing is used to take advantage of low-voltage
requirements, component matching, very low input-offset errors, and small component geometries.
The omnipolar operation of the A3245 allows activation with either a north or
a south polarity field of sufficient strength. In the absence of a magnetic field,
the output is off. This patented magnetic-polarity-independence feature makes
this device an excellent replacement for reed switches, with improved ease of
manufacturing, because the A3245 does not require manufacturers to orient their
magnets. These devices allow simple on/off switching in industrial, consumer, and
automotive applications.
The A3245 is rated for operation between the ambient temperatures –40°C and
85°C for the E temperature range, and –40°C to 150°C for the L temperature
range. The small geometries of the BiCMOS process allow these devices to be
provided in ultrasmall packages. The package styles available provide magnetically optimized solutions for most applications. Package LH is an SOT23W, a
miniature low-profile surface-mount package, while package UA is a three-lead
ultramini SIP for through-hole mounting. Each package is available in a lead (Pb)
free version, with 100% matte tin plated leadframes.
Features and Benefits
Omnipolar operation
Output short circuit protection
Chopper stabilization
Solid state reliability
Superior temperature stability
Extremely low switchpoint drift
Insensitive to physical stress
Reverse battery protection
Small size
Robust EMC capability
High ESD ratings (HBM)
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Product Selection Guide
Part Number
Pb-Free
A3245ELHLT
–
A3245ELHLT-T
Yes
A3245LLHLT
–
A3245LLHLT-T
Yes
A3245LUA
Bulk, 500 pieces/bag
3-pin SIP through hole
7-in. reel, 3000 pieces/reel
3-pin SOT23W surface mount
–40 to 150
–
A3245LUA-T
3-pin SOT23W surface mount
–40 to 85
–
A3245EUA-T
Ambient, TA
(°C)
Mounting
7-in. reel, 3000 pieces/reel
Yes
A3245EUA
Packing*
Bulk, 500 pieces/bag
Yes
3-pin SIP through hole
*Contact Allegro for additional packing options.
Functional Block Diagram
VCC
Regulator
Amp
Low-Pass
Filter
Amp
Sample and Hold
Dynamic Offset
Cancellation
To All Subcircuits
VOUT
Control
Current Limit
<1Ω
GND
Terminal List
Name
Description
Number
Package LH
Package UA
Connects power supply to chip
1
1
VOUT
Output from circuit
2
3
GND
Ground
3
2
VCC
2
A3245-DS, Rev. 1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
OPERATING CHARACTERISTICS valid over full operating voltage and ambient temperature ranges, unless otherwise noted
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
Electrical Characteristics
Supply Voltage1
Output Leakage Current
VCC
Operating, TJ < 165°C
3.6
–
24
V
IOUTOFF
VOUT = 24 V, B < BRP
–
–
10
μA
VOUT(SAT)
IOUT = 20 mA, B > BOP
–
–
500
mV
Output Current Limit
IOM
B > BOP
30
–
60
mA
Power-On Time
tPO
VCC > VCC(MIN)
–
–
50
μs
–
200
–
kHz
Output On Voltage
Chopping Frequency
fc
Output Rise Time2
tr
RLOAD = 820 Ω, CS = 20 pF
–
–
1
μs
Output Fall Time2
tf
RLOAD = 820 Ω, CS = 20 pF
–
–
1
μs
ICCON
B > BOP
–
1.5
3.5
mA
ICCOFF
B < BRP
–
1.5
3.5
mA
VRCC = –18 V
–
–
–2
mA
VZSupply
ICC = 6.5 mA; TA = 25°C
28
–
–
V
IZSupply
VS = 28 V
–
–
6.5
mA
BOPS
South pole adjacent to branded face of device
15
38
55
G
BOPN
North pole adjacent to branded face of device
–55
–38
–15
G
BRPS
South pole adjacent to branded face of device
5
20
50
G
BRPN
North pole adjacent to branded face of device
–50
–20
–5
G
BHYS
|BOPX – BRPX|
5
18
30
G
Supply Current
Reverse Battery Current
Supply Zener Clamp Voltage
Supply Zener
Current3
IRCC
Magnetic Characteristics4
Operate Point
Release Point
Hysteresis
1
Maximum voltage must be adjusted for power dissipation and junction temperature, see Power Derating section.
CS = oscilloscope probe capacitance.
3 Maximum current limit is equal to the maximum I
CC(MAX) + 3 mA.
4 Magnetic flux density, B, is indicated as a negative value for north-polarity magnetic fields, and as a positive value for south-polarity magnetic fields.
This so-called algebraic convention supports arithmetic comparison of north and south polarity values, where the relative strength of the field is indicated
by the absolute value of B, and the sign indicates the polarity of the field (for example, a –100 G field and a 100 G field have equivalent strength, but
opposite polarity).
2
DEVICE QUALIFICATION PROGRAM
Contact Allegro for information.
EMC (Electromagnetic Compatibility) REQUIREMENTS
Contact Allegro for information.
3
A3245-DS, Rev. 1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Electrical Characteristic Data
Supply Current (On) versus Ambient Temperature
Supply Current (On) versus Supply Voltage
5.0
5.0
4.0
VCC (V)
3.0
24
3.6
2.0
ICCON (mA)
ICCON (mA)
4.0
1.0
3.0
–40
25
150
2.0
1.0
0
–50
TA (°C)
0
0
50
TA (°C)
100
150
0
25
4.0
VCC (V)
3.0
24
3.6
2.0
ICCOFF (mA)
ICCOFF (mA)
20
5.0
4.0
TA (°C)
–40
25
150
3.0
2.0
1.0
1.0
0
0
0
50
TA (°C)
100
0
150
5
10
15
20
25
VCC (V)
Output Voltage (On) versus Ambient Temperature
Output Voltage (On) versus Supply Voltage
500
500
450
450
400
400
350
350
300
VCC (V)
250
24
3.6
200
150
VOUT(SAT) (mV)
VOUT(SAT) (mV)
15
Supply Current (Off) versus Supply Voltage
5.0
TA (°C)
300
–40
25
150
250
200
150
100
100
50
50
0
–50
10
VCC (V)
Supply Current (Off) versus Ambient Temperature
–50
5
0
0
50
TA (°C)
100
150
0
5
10
15
20
25
VCC (V)
4
A3245-DS, Rev. 1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Magnetic Characteristic Data
Operate Point (South) versus Ambient Temperature
55
-15
50
-20
45
-25
40
-30
VCC (V)
35
BOPN (G)
BOPS (G)
Operate Point (North) versus Ambient Temperature
24
3.6
30
-45
20
-50
–50
-55
0
50
TA (°C)
100
–50
150
Release Point (South) versus Ambient Temperature
0
50
TA (°C)
100
150
Release Point (North) versus Ambient Temperature
50
-5
45
-10
40
-15
-20
30
VCC (V)
25
24
3.6
20
BRPN (G)
35
BRPS (G)
24
3.6
-40
25
15
VCC (V)
-35
-25
VCC (V)
-30
24
3.6
-35
15
-40
10
-45
5
-50
–50
0
50
TA (°C)
100
150
–50
0
50
TA (°C)
100
150
Hysteresis versus Ambient Temperature
30
BHYS (G)
25
20
VCC (V)
15
24
3.6
10
5
–50
0
50
100
150
TA (°C)
Continued on the next page...
5
A3245-DS, Rev. 1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Magnetic Characteristic Data (Continued)
Operate Point (South) versus Supply Voltage
Operate Point (North) versus Supply Voltage
55
-15
50
-20
-25
40
TA (°C)
35
–40
25
150
30
BOPN (G)
BOPS (G)
45
TA (°C)
-35
–40
25
150
-40
25
-45
20
-50
15
0
5
10
15
20
-55
25
0
5
10
15
20
25
VCC (V)
VCC (V)
Release Point (South) versus Supply Voltage
Release Point (North) versus Supply Voltage
50
-5
45
-10
40
-15
35
-20
TA (°C)
30
–40
25
150
25
20
BRPN (G)
BRPS (G)
-30
–40
25
150
-30
-35
15
-40
10
-45
5
TA (°C)
-25
-50
0
5
10
15
20
25
0
5
10
VCC (V)
15
20
25
VCC (V)
Hysteresis versus Supply Voltage
30
BHYS (G)
25
TA (°C)
20
–40
25
150
15
10
5
0
5
10
15
20
25
VCC (V)
6
A3245-DS, Rev. 1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic
Symbol
RθJA
Package Thermal Resistance
Test Conditions
Package LH-3, 1-layer PCB with copper limited to
solder pads
Package LH-3, 2-layer PCB with 0.926 in2 on each
side, connected by thermal vias
Package UA, 1-layer PCB with copper limited to
solder pads
Value
Units
110
ºC/W
228
ºC/W
165
ºC/W
Maximum Allowable V CC (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
V CC(max)
1-layer PCB, Package LH
(R θJA= 110 °C/W)
1-layer PCB, Package UA
(R θJA= 165 °C/W)
2-layer PCB, Package LH
(R θJA= 228 °C/W)
V CC(min)
20
40
60
80
100
120
140
160
180
Temperature (°C)
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
1l
(R aye
rP
θJ
C
A =
11 B, P
0 º ac
1-la
C/ ka
W
(R yer P
) ge L
CB
θJA =
H
165 , Pac
k
ºC/
a
W) ge U
A
2-la
y
(R er PCB
,
θJA =
228 Packa
ºC/W ge L
H
)
20
40
60
80
100
120
Temperature (°C)
140
160
180
7
A3245-DS, Rev. 1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Functional Description
Operation
The output of this device switches low (turns on) when a magnetic field perpendicular to the Hall sensor exceeds the operate
point, BOPS (or is less than BOPN). After turn-on, the output
voltage is VOUT(SAT). The output transistor is capable of sinking current up to the short circuit current limit, IOM, which is a
minimum of 30 mA. When the magnetic field is reduced below
the release point, BRPS (or increased above BRPN), the device
output switches 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.
Powering-on the device in a hysteresis region, between BOPX
and BRPX, allows an indeterminate output state. The correct state
is attained after the first excursion beyond BOPX or BRPX.
Applications
It is strongly recommended that an external bypass capacitor be
connected (in close proximity to the Hall sensor) between the
supply and ground of the device to reduce both external noise
and noise generated by the chopper stabilization technique. As is
shown in Panel B of figure 1, a 0.1μF capacitor is typical.
Omnipolar switches allow operation with either a north pole or
south pole magnet orientation, enhancing product manufacturability with the device.
Extensive applications information on magnets and Hall-effect
sensors is available in:
• Hall-Effect IC Applications Guide, AN27701,
• Hall-Effect Devices: Gluing, Potting, Encapsulating, Lead
Welding and Lead Forming, AN27703.1
• Soldering Methods for Allegro’s Products – SMT and ThroughHole, AN26009
All are provided in Allegro Electronic Data Book, AMS-702 and
the Allegro Web site: www.allegromicro.com
(B)
(A)
V+
Switch to High
VOUT
VS
VCC
CBYP
0.1 μF
A3245
RLOAD
VOUT
Sensor Output
VOUT(SAT)
BHYS
BRPS
0
BOPS
BOPN
B–
BRPN
0
Switch to Low
Switch to Low
Switch to High
VS
B+
GND
BHYS
Figure 1: Switching Behavior of Omnipolar Switches. In Panel A, on the horizontal axis, the B+ direction indicates increasing south polarity
magnetic field strength, and the B– direction indicates decreasing south polarity field strength (including the case of increasing north
polarity). This behavior can be exhibited when using a circuit such as that shown in panel B.
8
A3245-DS, Rev. 1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Chopper Stabilization Technique
When using Hall-effect technology, a limiting factor for
switchpoint accuracy is the small signal voltage developed
across the Hall element. This voltage is disproportionally small
relative to the offset that can be produced at the output of the
Hall sensor. This makes it difficult to process the signal while
maintaining an accurate, reliable output over the specified operating temperature and voltage ranges.
Chopper stabilization is a unique approach used to minimize
Hall offset on the chip. The patented Allegro technique, namely
Dynamic Quadrature Offset Cancellation, removes key sources
of the output drift induced by thermal and mechanical stresses.
This offset reduction technique is based on a signal modulationdemodulation process. The undesired offset signal is separated
from the magnetic-field-induced signal in the frequency domain,
through modulation. The subsequent demodulation acts as a
modulation process for the offset, causing the magnetic-fieldinduced signal to recover its original spectrum at baseband,
while the dc offset becomes a high-frequency signal. The magnetic-field-induced signal then can pass through a low-pass filter,
while the modulated dc offset is suppressed. This configuration
is illustrated in figure 2.
The chopper stabilization technique uses a 200 kHz high-frequency clock. For demodulation process, a sample and hold
technique is used, where the sampling is performed at twice the
chopper frequency (400 kHz). This high-frequency operation
allows a greater sampling rate, which results in higher accuracy
and faster signal-processing capability. This approach desensitizes the chip to the effects of thermal and mechanical stresses,
and produces devices that have extremely stable quiescent Hall
output voltages and precise recoverability after temperature
cycling. This technique is made possible through the use of a
BiCMOS process, which allows the use of low-offset, low-noise
amplifiers in combination with high-density logic integration and
sample-and-hold circuits.
The repeatability of magnetic-field-induced switching is affected
slightly by a chopper technique. However, the Allegro highfrequency chopping approach minimizes the affect of jitter and
makes it imperceptible in most applications. Applications that
are more likely to be sensitive to such degradation are those
requiring precise sensing of alternating magnetic fields; for
example, speed sensing of ring-magnet targets. For such applications, Allegro recommends its digital sensor families with lower
sensitivity to jitter. For more information on those devices,
contact your Allegro sales representative.
Regulator
Amp
Low-Pass
Filter
Hall Element
Sample and
Hold
Clock/Logic
Figure 2. Chopper Stabilization Circuit (Dynamic Quadrature Offset Cancellation)
9
A3245-DS, Rev. 1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Power Derating
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. This section presents a procedure for correlating
factors affecting operating TJ. (Thermal data is also available on
the Allegro MicroSystems Web site.)
The Package Thermal Resistance, RθJA, is a figure of merit summarizing the ability of the application and the device to dissipate
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.
The effect of varying power levels (Power Dissipation, PD), can
be estimated. The following formulas represent the fundamental
relationships used to estimate TJ, at PD.
PD = VIN × IIN
(1)
ΔT = PD × RθJA
(2)
TJ = TA + ΔT
(3)
Example: Reliability for VCC at TA = 150°C, package LH, using a
low-K PCB.
Observe the worst-case ratings for the device, specifically:
RθJA = 228 °C/W, TJ(max) = 165°C, VCC(max) = 24 V, and
ICC(max) = 5 mA.
Calculate the maximum allowable power level, PD(max). First,
invert equation 3:
ΔTmax = TJ(max) – TA = 165 °C – 150 °C = 15 °C
This provides the allowable increase to TJ resulting from internal
power dissipation. Then, invert equation 2:
PD(max) = ΔTmax ÷ RθJA = 15°C ÷ 228 °C/W = 65.8 mW
Finally, invert equation 1 with respect to voltage:
VCC(est) = PD(max) ÷ ICC(max) = 65.8 mW ÷ 5 mA = 13.2 V
The result indicates that, at TA, the application and device can
dissipate adequate amounts of heat at voltages ≤VCC(est).
Compare VCC(est) to VCC(max). If VCC(est) ≤ VCC(max), then reliable operation between VCC(est) and VCC(max) requires enhanced
RθJA. If VCC(est) ≥ VCC(max), then operation between VCC(est) and
VCC(max) is reliable under these conditions.
For example, given common conditions such as: TA= 25°C,
VCC = 12 V, ICC = 1.5 mA, and RθJA = 165 °C/W, then:
PD = VCC × ICC = 12 V × 1.5 mA = 18 mW
ΔT = PD × RθJA = 18 mW × 165 °C/W = 3°C
TJ = TA + ΔT = 25°C + 3°C = 28°C
A worst-case estimate, PD(max), represents the maximum allowable power level (VCC(max), ICC(max)), without exceeding TJ(max),
at a selected RθJA and TA.
10
A3245-DS, Rev. 1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
Package LH, 3-Pin (SOT-23W)
Package UA, 3-Pin
11
A3245-DS, Rev. 1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3245
Chopper-Stabilized Omnipolar Hall Effect Switches
The products described herein are manufactured under one
or more of the following U.S. patents: 5,045,920; 5,264,783;
5,442,283; 5,389,889; 5,581,179; 5,517,112; 5,619,137; 5,621,319;
5,650,719; 5,686,894; 5,694,038; 5,729,130; 5,917,320; and other
patents pending.
Allegro MicroSystems, Inc. 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 products are not authorized for use as critical components in life-support devices or systems without express written
approval.
The information included herein is believed to be accurate and
reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other
rights of third parties which may result from its use.
Copyright © 2005 Allegro MicroSystems, Inc.
12
A3245-DS, Rev. 1
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
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