*Patent Pending
MLX90215 Programmable Hall Effect Sensor
Rev 4.3
7/6/01
Page 9
MLX90215
Precision Programmable*
Linear Hall Effect Sensor
ApplicationNotes
5
4
3
2
1
0
0
-100
100
Current (Amps)
MLX
90215
V
DD
A slotted ferrite
toroidal core and a
series of windings are
the main elements of a
current sensor. By
adding a
programmable Hall IC
to the air gap, not only
can the output be
calibrated accurately,
but it can also be
adjusted to respond to
virtually any range of
current
Programmable Current Sensor
LinearPrecisionCurrentSensor
The Programmable gain, offset, and temperature co m-
pensation of MLX90215 allows great flexiblity in the
design of a current sensor.
Current flowing through a conductor can produce a
proportional magnet field. The MLX90215 can then
produce an output voltage proportional to the current.
Using the programmable gain and offset function the
output of the MLX90215 can be adjusted to sense a
wide range of current allowing for a flexib le design.
Slotted Torroid Example Assuming infinite perme-
abilty of the core, the magnetic field through the air
gap produced by a single wire turn is given by equa-
tion 2
Equation 2
Where: I = current in Amperes
B = magnetic field in Tesla
lg = length of air gap in Meters
uo = Permeability of free space (4π10
-7H/m)
This equation is a close estimate for the field in the air
gap, but does not take into account magnetic losses in
the core, fringing effects, and mechanical tolerances of
the air gap.
The programmable MLX90215 can be
adjusted to compensate for these errors simplifying the
design. The temperature compensation of MLX90215
can also be adjusted to counteract temperature losses
of core.
For sensing a current ±100A, with an air gap of 2mm
equation 2 yields a magnetic field range of ±63mT.
The output range of the MLX90215 is 0.5V to 4.5V
(4V full scale). Equations 3a and 3b yield a sensitivity
of 32mV/mT and a Voq of 2.5V.
Equation 3
a) S = 4000mV/ 126mT
b) Voq = 4V/2 + 0.5V
The resulting gain of the current sensor is 20mV/A
with an offset of 2.5V. For best results it is recommend
that MLX90215 be programmed with a Voq of 50%
Vdd 1/2 Vdd bit set.
o
g
u
l
I
B
=
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