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A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
Discontinued Product
This device is no longer in production. The device should not be
purchased for new design applications. Samples are no longer available.
Date of status change: October 31, 2011
Recommended Substitutions:
• for the A1242ELHLT-I2-T use the A1244LLHLX-I2-T
• for the A1242ELHLT-I1-T use the A1244LLHLX-I1-T
• for the A1242LLHLT-I2-T use the A1244LLHLX-I2-T
• for the A1242LLHLT-I1-T use the A1244LLHLX-I1-T
• for the A1242EUA-I1-T and A1242LUA-I1-T use the A1244LUA-I1-T
• for the A1242LUA-I2-T use the A1244LUA-I2-T
NOTE: For detailed information on purchasing options, contact your
local Allegro field applications engineer or sales representative.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, revisions to the anticipated product life cycle plan
for a product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The
information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no respon-
sibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use.
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A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
Features and Benefits
Chopper stabilization
Superior temperature stability
Extremely low switchpoint drift
Insensitive to physical stress
Reverse battery protection
Solid-state reliability
Small size
Robust EMC capability
High ESD ratings (HBM)
Packages: 3 pin SOT23W (suffix LH), and
3 pin SIP (suffix UA)
Description
The A1242 Hall effect latch is a two-wire latch especially
suited for operation over extended temperature ranges, from
–40 to +150°C. Superior high-temperature performance is
made possible through the Allegro® patented dynamic offset
cancellation technique, which reduces the residual offset
voltage normally caused by device overmolding, temperature
dependencies, and thermal stress.
The current-switching output technique allows for the reduction
in cost in the wiring harness because only two connections to
the device are required. The current-switching output structure
also inherently provides more immunity against EMC/ESD
transients. These devices have low magnetic thresholds, thereby
enabling more flexibility in the magnetic circuit design.
The Hall effect latch will be in the high output current state
in the presence of a magnetic South Pole field of sufficient
magnitude and will remain in this state until a sufficient North
Pole field is present.
The A1242 includes the following on a single silicon chip:
a voltage regulator, Hall-voltage generator, small-signal
amplifier, chopper stabilization, Schmitt trigger, and a current
source output. Advanced BiCMOS wafer fabrication processing
takes advantage of low-voltage requirements, component
Not to scale
Continued on the next page…
Functional Block Diagram
VCC
Clock/Logic
Amp
Regulator
To All Subcircuits
Low-Pass
Filter
1242-DS, Rev. 6
GND
Package UA Only
GND
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A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
Description (continued)
matching, very low input-offset errors and small component
geometries.
Suffix ‘L-’ devices are rated for operation over a temperature range
of –40°C to +150°C; suffix ‘E-’ devices are rated for operation over
a temperature range of –40°C to +85°C. Two A1242 package styles
provide magnetically optimized solutions for most applications.
Package LH is a SOT23W, a miniature low-profile surface-mount
package, while package UA is a three-pin ultramini SIP for through-
hole mounting. Each package is available lead (Pb) free, with 100%
matte tin plated leadframes.
Selection Guide
Part Number
Packaging*
A1242ELHLT-I1-T
A1242ELHLT-I2-T
7-in. reel, 3000 pieces/reel
A1242EUA-I1-T
Bulk, 500 pieces/bag
A1242LLHLT-I1-T
A1242LLHLT-I2-T
7-in. reel, 3000 pieces/reel
A1242LUA-I1-T
A1242LUA-I2-T
Bulk, 500 pieces/bag
*Contact Allegro for additional packing options.
Mounting
3-pin SOT23W surface mount
3-pin SIP through hole
3-pin SOT23W surface mount
3-pin SIP through hole
Low Current, ICC(L)
(mA)
5.0 to 6.9
2.0 to 5.0
5.0 to 6.9
5.0 to 6.9
2.0 to 5.0
5.0 to 6.9
2.0 to 5.0
Ambient, TA
(°C)
–40 to 85
–40 to 150
BRP(MIN)
(G)
–80
BOP(MAX)
(G)
80
Absolute Maximum Ratings
Characteristic
Supply Voltage
Reverse Supply Voltage
Magnetic Flux Density
Symbol
VCC
VRCC
B
Operating Ambient Temperature
TA
Maximum Junction Temperature
Storage Temperature
*1 G (gauss) = 0.1 mT (millitesla)
TJ(max)
Tstg
Pin-out Diagrams
LH Package
UA Package
3
NC
12
123
Notes
Range E
Range L
Rating
28
–18
Unlimited
–40 to 85
–40 to 150
165
–65 to 170
Unit*
V
V
G
ºC
ºC
ºC
ºC
Terminal List
Name
VCC
Number
Package LH Package UA
Function
1 1 Connects power supply to chip
GND
3
2,3 Ground
NC 2
– No internal connection
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
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A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
ELECTRICAL CHARACTERISTICS over full operating voltage and temperature ranges, unless otherwise specified
Characteristic
Symbol
Test Conditions
Min. Typ.1 Max. Units
Electrical Characteristics
Supply Voltage2 3
Supply Current
Output Slew Rate4
Chopping Frequency
Power-On Time
Power-On State5
Supply Zener Clamp Voltage
Supply Zener Current6
Reverse Battery Current
Magnetic Characteristics7
VCC
ICC(L)
ICC(H)
dI/dt
fC
tPO
POS
VZ(supply)
IZ(supply)
IRCC
Operating, TJ < 165°C
-I1, B < BRP
-I2, B < BRP
-I1 and -I2, B > BOP
RS = 100 Ω, CS = 20 pF, no bypass capacitor
VCC > VCC(MIN)
tPO < tPO(max), dVCC / dt > 25 mV / μs
ICC = 20 mA; TA = 25°C
VS = 28 V
VRCC = –18 V
3.5 – 24 V
5 – 6.9 mA
2 – 5 mA
12 – 17 mA
– 36 – mA/μs
– 200 – kHz
– – 25 μs
– ICC(H)
28 –
V
– – 20 mA
– – 2.5 mA
Operate Point
BOP South pole adjacent to branded face of device
5 32 80 G
Release Point
BRP North pole adjacent to branded face of device
–80 –32
–5
G
Hysteresis
BHYS
BOP – BRP
40 64 110 G
1 Typical values are at TA = 25°C and VCC = 12 V. Performance may vary for individual units, within the specified maximum and mini-
mum limits.
2 Maximum voltage must be adjusted for power dissipation and junction temperature; see Power Derating section.
3 VCC represents the generated voltage between the VCC pin and the GND pin.
4 The value of dI is the difference between 90% of ICC(H) and 10% of ICC(L), and the value of dt is time period between those two
points. The value of dI/dt depends on the value of the bypass capacitor, if one is used, with greater capacitances resulting in lower
rates of change.
5 For t > tPO(max), and BRP < B < BOP, POS is undefined.
6 Maximum current limit is equal to the maximum ICCL(max) + 3 mA.
7 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 rela-
tive 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).
DEVICE QUALIFICATION PROGRAM
Contact Allegro for information.
EMC (Electromagnetic Compatibility) PERFORMANCE
Contact Allegro for information.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
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A1242
Two-Wire Chopper-Stabilized Hall Effect Latch
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic
Package Thermal Resistance
Symbol
RθJA
Test Conditions*
Package LH, minimum-K PCB (single layer, single-sided with
copper limited to solder pads)
Package LH, low-K PCB (single layer, double-sided with
0.926 in2 copper area)
Package UA, minimum-K PCB (single layer, single-sided with
copper limited to solder pads)
*Additional information available on the Allegro Web site.
Power Derating Curve
TJ(max) = 165°C; ICC = ICC(max)
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
Low-K PCB, Package LH
9
8
7
(R JA = 110 °C/W)
Minimum-K PCB, Package UA
6
5
4
(R JA = 165 °C/W)
Minimum-K PCB, Package LH
3
2
(R JA = 228 °C/W)
20 40 60 80 100 120 140 160
Temperature (°C)
VCC(max)
VCC(min)
180
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
Low-K PCB, Package LH
(R JA = 110 °C/W)
Min-K PCB, Package UA
(R JA = 165 °C/W)
Min-K PCB, Package LH
(R JA = 228 °C/W)
20 40 60 80 100 120 140
Temperature (°C)
160
180
Value Units
228 ºC/W
110 ºC/W
165 ºC/W
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
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