The A3150JLT and A3150JUA programmable switches provide
tooth/valley recognition in large gear-tooth sensing applications. Each
sensor consists of a single element, chopper-stabilized Hall-effect IC
X
PTCT
V
CC
1
32
that can be programmed to the desired magnetic switch point, optimizing sensor airgap and timing accuracy performance after final
packaging. The small package can be easily assembled and used in
conjunction with a wide variety of gear/target shapes and sizes. The
two devices differ only in package style.
The sensing technology used for this sensor is Hall-effect based.
The sensor incorporates a single-element Hall IC that switches in
response to magnetic signals created by a ferrous target. The programmability of the circuit eliminates magnet and system offsets such as
those caused by tilt yet provides zero-speed detection capabilities
without the associated running jitter inherent in classical digital solutions.
A proprietary dynamic offset cancelation technique, with an
SUPPLY
GROUND
Dwg. PH-003-2
PRELIMINARY INFORMATION
(subject to change without notice)
April 12, 1999
ABSOLUTE MAXIMUM RATINGS
at T
= 25°C
A
Supply Voltage, VCC........................... 26.5 V
Reverse Supply Voltage, V
Overvoltage Supply Current, ICC..... 100 mA
Magnetic Flux Density, B ............ Unlimited
DISCONTINUED PRODUCT
Output Current, I
Output OFF Voltage, V
Reverse Output Current, I
Operating Temperature Range,
TA............................... -40°C to +115°C
Storage Temperature, TS................... +170°C
— FOR REFERENCE ONLY.
..... Internally Limited
OUT
OUT
Use A3250 for new design
OUTPUT
............ -30 V
RCC
................. 26.5 V
......... -50 mA
ROUT
internal high-frequency clock, reduces the residual offset voltage,
which is normally caused by device overmolding, temperature
dependancies, and thermal stress. This technique produces devices that
have an extremely stable quiescent output voltage, are immune to
mechanical stress, and have precise recoverability after temperature
cycling. Many problems normally associated with low-level analog
signals are minimized by having the Hall element and amplifier in a
single chip. Output precision is obtained by internal gain adjustments
during the manufacturing process and operate-point programming in the
user’s application.
This sensor system is ideal for use in gathering speed, position, and
timing information using gear-tooth-based configurations. The
A3150JLT/JUA are particularly suited to those applications that require
accurate duty cycle control or accurate edge detection. The lower
vibration sensitivity also makes these devices extremely useful for
transmission speed sensing.
Continued next page
Always order by complete part number: the prefix 'A' + the basic four-digit
part number + a suffix to indicate operating temperature range +
a suffix to indicate package style, e.g., A3150JLT .
Two package styles provide a magnetically optimized package for most applications. Suffix ‘–LT’ is a
miniature SOT-89/TO-243AA transistor package for
surface-mount applications; while suffix ‘–UA’ is a
three-lead ultra-mini-SIP for through-hole mounting.
Chopper-Stabilized Technique. These devices use a
proprietary dynamic offset cancellation technique, with an
internal high-frequency clock to reduce the residual offset
voltage of the Hall element that is normally caused by device
overmolding, temperature dependencies, and thermal stress.
This technique produces devices that have an extremely stable
quiescent Hall output voltage, are immune to thermal stress, and
have precise recoverability after temperature cycling. This
technique will also slightly degrade the device output repeatability.
The Hall element can be considered as a resistor array
similar to a Wheatstone bridge. A large portion of the offset is a
result of the mismatching of these resistors. The chopperstabilizing technique cancels the mismatching of the resistors by
changing the direction of the current flowing through the Hall
plate and Hall voltage measurement taps, while maintaining the
Hall-voltage signal that is induced by the external magnetic flux.
The signal is, then, captured by a sample-and-hold circuit.
Operation. The output of these devices switches low (turns
ON) when a magnetic field (south pole) perpendicular to the
Hall sensor exceeds the operate point threshold (BOP). After
turn-ON, the output is capable of sinking 25 mA and the output
voltage is V
OUT(SAT)
. When the magnetic field is reduced below
the release point (BRP), the device output goes high (turns OFF).
The difference in the magnetic operate and release points is the
hysteresis (B
) of the device. This built-in hysteresis allows
hys
clean switching of the output even in the presence of external
mechanical vibration and electrical noise.
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.
B
+V
+V
V
CC
OUTPUT VOLTAGE
0
0
REG
X
—
HALL
VOLTAGE
+
Dwg. AH-011-2
B
RP
FLUX DENSITY
& HOLD
SAMPLE
Dwg. EH-012
B
OP
V
OUT(SAT)
+B
Dwg. GH-007-2
SUPPLY
The simplest form of magnet that will operate these devices
is a bar magnet with the south-seeking pole towards the branded
surface of the device. Many other methods of operation are
possible. Extensive applications information on magnets and
Hall-effect sensors is also available in the Allegro ElectronicData Book AMS-702 or Application Note 27701, or
The A3150JLT and A3150JUA operate points are programmed by serially addressing the device through the
supply terminal (pin1). After the correct operate point is
determined, the device programming bits are selected and
then a “lock” set to prevent any further (accidental)
programming.
Program Enable. To program the device, a sequence of
pulses is used to activate/enable the addressing mode as
shown in figure 1. This sequence of a V
seven VPH pulses, and a VPP pulse with no supply interruptions, is designed to prevent the device from being programmed accidentally (for example, as a result of noise on
the supply line).
pulse, at least
PP
V
PP
V
PH
V
PL
t
d(1)
0
PROGRAM ENABLE
(AT LEAST 7 PULSES)
t
d(1)
t
d(0)
Dwg. WH-013
Figure 1 — Program enable
PROGRAMMING PROTOCOL over operating temperature range.
Limits
CharacteristicSymbolDescriptionMin.Typ.Max.Units
Programming VoltageV
Programming CurrentI
Pulse Widtht
Pulse Rise Timet
Pulse Fall Timet
V
V
t
PP
d(0)
d(1)
t
dP
PL
PH
PP
r
f
NOTE: Typical data is at TA = +25°C and is for design information only.
Address Determination. The operate point is adjust-
A
able in 64 increments. With the appropriate target or gear*
in position, the 64 switch points are sequentially selected
(figure 2) until the required operate point is reached. Note
that the difference between the operate point and the
release point (hysteresis) is a constant for all addresses.
Set-Point Programming. After the desired set-point
address is determined (0 through 63), each bit of the
equivalent binary address is programmed individually. For
example, as illustrated in figure 3, to program address code
5 (binary 000101), bits 1 and 3 need to be programmed.
Each bit is programmed during the
wide V
pulse and is not reversible.
PP
PROGRAMMABLE, CHOPPER-
STABILIZED, PRECISION,
HALL-EFFECT SWITCH
VPH
VPL
ADDRESS 0
ADDRESS 1
ADDRESS 2
0
td(1)td(0)
Figure 2 — Address determination
ADDRESS N-2
3150
ADDRESS N-1
Dwg. WH-014
ADDRESS N
(UP TO 63)
Lock Programming. After the desired set point is
programmed, the program lock is then activated (figure 4)
to prevent further programming of the device.
V
PP
V
PH
V
PL
0
t
d(1)
PROGRAM ENABLE
t
d(1)
BIT 3 PROGRAM
(000100)
ADDRESS 4
t
d(0)
Figure 3 — Set-point programming
V
PP
V
PH
V
PL
0
t
d(1)
PROGRAM ENABLELOCK PROGRAM
t
d(1)
t
d(0)
Figure 4 — Lock programming
PROGRAM ENABLE
BIT 1 PROGR
t
dP
Dwg. WH-015
(65 PULSES)
t
dP
Dwg. WH-016
* In application, the terms “gear” and “target” are often
interchanged. However, “gear” is preferred when motion
is transferred.
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 appliances, 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 infringements of patents or other rights of
third parties that may result from its use.