A1242 ALLEGRO [Allegro MicroSystems], A1242 Datasheet - Page 7

• Manufacturer Part Number: A1242
• Description: Two-Wire Chopper-Stabilized Hall Effect Latch
• Manufacturer: ALLEGRO [Allegro MicroSystems]

OPERATION
The output, I
when a magnetic field perpendicular to the Hall sensor exceeds
the operate point threshold, B
that is, a south pole of sufficient strength towards the branded
surface of the device switches the device output to I
device retains its output state if the south pole is removed. When
the magnetic field is reduced to below the release point thresh-
old, B
ference between the magnetic operate and release points is called
the hysteresis of the device, B
clean switching of the output even in the presence of external
mechanical vibration and electrical noise.
.
TYPICAL APPLICATION CIRCUIT
The A1242 should be protected by an external bypass capaci-
tor, C
GND, of the device. C
noise generated by the chopper-stabilization function. As shown
in figure 2, a 0.01 μF capacitor is typical.
Installation of C
the A1242 pins are no greater than 5 mm in length.
All high-frequency interferences conducted along the supply
lines are passed directly to the load through C
only to protect the A1242 internal circuitry. As a result, the load
ECU (electronic control unit) must have sufficient protection,
other than C
A series resistor on the supply side, R
tion with C
When determining the minimum V
device, the voltage drops across R
R
R
A1242-DS
SENSE
SENSE
BYP
RP
, must be taken into consideration. The typical value for
is approximately 100 Ω.
, the device output goes to the low current state. The dif-
, connected between the supply, V
BYP
BYP
CC
, creates a filter for EMI pulses.
, of the A1242 switches to the high current state
, installed in parallel with the A1242.
BYP
must ensure that the traces that connect it to
BYP
reduces both external noise and the
OP
HYS
Two-Wire Chopper-Stabilized Hall Effect Latch
. Note that the device latches,
. This built-in hysteresis allows
S
CC
and the ECU sense resistor,
S
requirement of the A1242
(not shown), in combina-
CC
, and the ground,
BYP
, and it serves
Functional Description
CC(H)
. The
A1242
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
• Soldering Methods for Allegro Products – SMD and Through-Hole,
All are provided in Allegro Electronic Data Book, AMS-702
and the Allegro Web site: www.allegromicro.com.
Figure 1. Switching Behavior of the A1242. 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).
Figure 2. Typical Application Circuit
and Lead Forming, AN27703.1
AN26009
I+
0
V+
B–
A
GND
A1242
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
ECU
VCC
B
R
HYS
SENSE
GND
0
A
B
Package UA Only
Maximum separation 5 mm
B
B
B+
C
0.01 uF
I
I
BYP
CC(H)
CC(L)
7