3425 Datasheet, PDF (9/12 Pages) Allegro MicroSystems – DUAL, CHOPPER-STABILIZED, ULTRA-SENSITIVE, BIPOLAR HALL-EFFECT SWITCH

3425
DUAL, CHOPPER-STABILIZED,
ULTRA-SENSITIVE,
BIPOLAR HALL-EFFECT SWITCH
APPLICATIONS INFORMATION (cont'd)
Power Dissipation and Junction Temperature.
Operating characteristics are limited by allowable package
power dissipation (P_D) as a function of ambient tempera-
ture (T_A), which is defined by the maximum internal
junction temperature (T_J = 170°C) and the package
thermal resistance (R_θJA = 177°C/W).
P_D = (T_J – T_A)/R_θJA = (170 – T_A)/177
This is shown in the graph on page 2.
Actual or required package power dissipation is the
sum of the two output powers (d.c. x I_OUT1 x V_OUT(SAT)1) +
(d.c. x I_OUT2 x V_OUT(SAT)2) and the sensor power (I_CC x
V_CC).
At high ambient operating temperatures (above about
120°C), it is easy to exceed the allowable package power
dissipation. In this case, the output currents or the supply
voltage must be reduced.
Operation with Fine-Pitch Ring Magnets. For
targets with a circular pitch of less than 4 mm, a perfor-
mance improvement can be observed by rotating the front
face of the sensor subassembly (see below). This sensor
rotation decreases the effective sensor-to-sensor spacing,
provided that the Hall elements are not rotated beyond the
width of the target.
Applications. It is strongly recommended that an
external 0.01 µF 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 internal logic.
The simplest form of magnet that will operate these
devices is a ring magnet. Other methods of operation,
such as linear magnets, are possible. Extensive applica-
tions information on magnets and Hall-effect sensors is
also available in the “Hall-Effect IC Applications Guide”
which can be found in the latest issue of the Allegro
MicroSystems Electronic Data Book, AMS-702 or Appli-
cation Note 27701, or at
www.allegromicro.com
0.039"
1.00 mm
A
1
2
3
4
α
TARGET FACE WIDTH, F
>1.00 SIN α (mm)
>0.039 SIN α (inch)
A
1
2
3
4
www.allegromicro.com
Rotated sensor for
fine-pitch ring
magnets
Dwg. MH-024-1
9