A1351
High Precision Linear Hall Effect Sensor IC
with a Push/Pull, Pulse Width Modulated Output
21
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
To construct a current sensor using the A1351, first consider a
current carrying wire that we want to observe. As dictated by
Amperes Law, a magnetic field is produced around the wire
that is proportional to the amount of current flowing through
the wire. By passing this wire through a soft magnetic core, the
magnetic flux produced by the wire can be concentrated and
directed through a gap in the core. The magnetic flux density can
be measured by inserting the A1351 SIP into the gap in the core.
As a result, the output of the A1351 device will be proportional
to the amount of current flowing through the wire.
The example feedthrough current sensing setup shown below
(figure 7) has a core made of mu metal that is 2 mm thick
and 4 mm wide. The inner radius of the core is 14.5 mm and
the outer radius is 18.5 mm. The wire going through the center
of the core has a radius of 9 mm. Using this setup with a gap of
1.7 mm, a field strength results that is on the order of 7 G / A at
the Hall element in the A1351.
The recommended core material for construction of the concen-
trator depends on the specific application. If high flux saturation
is desired, then an alloy such as HyPerm49 is recommended.
For lower-current level sensing applications, a material such as
HyMu80 may be desired. (HyMu80 has lower magnetic flux
saturation than HyPerm49, therefore more HyMu80 mate-
rial is required to carry the same amount of flux compared
to Hyperm49.) If frequency response is a concern, then eddy
currents can be reduced by either laminating the HyPerm49 or
HyMu80 alloys, or by using a ferrite core.
Constructing a Current Sensor Using the A1351
?8 mm
4 mm
2 mm
?7 mm
Application-specific housing
Ring concentrator
Current-conducting wire
A136x
Center Hall element in gap
1.7 mm
Figure 7. The example current sensor setup used to generate the data in this section was
constructed with a split-ring concentrator and an A1351 device. A copper wire was fed
through the concentrator, and the A1351 placed in its gap. This approximates a typical
ammeter application on a thick wire, such as shown in the left view. Note that such
applications usually have a protective housing, which should be taken into consideration
when designing the nal application. The housing is beyond the scope of this example.