Data Sheet

2
HMC1501 / HMC1512 SENSOR PRODUCTS
Anisotropic magnetoresistance (AMR) occurs in ferrous
materials. It is a change in resistance when a magnetic
field is applied in a thin strip of ferrous material. The mag-
netoresistance is a function of cos
2
θ where θ is the angle
between magnetization M and current flow in the thin strip.
When an applied magnetic field is larger than 80 Oe, the
magnetization aligns in the same direction of the applied
field; this is called saturation mode. In this mode, θ is the
angle between the direction of applied field and the current
flow; the MR sensor is only sensitive to the direction of
applied field.
The sensor is in the form of a Wheatstone bridge (Figure 1).
The resistance R of all four resistors is the same. The bridge
power supply V
S
causes current to flow through the resistors,
the direction as indicated in the figure for each resistor.
Both HMC1501 and HMC1512 are designed to be used in
saturation mode. HMC1501 contains one MR bridge and
HMC1512 has two identical MR bridges, coexisting on a
single die. Bridge B physically rotates 45° from bridge A.
The HMC1501 has sensor output ∆V=-V
S
S sin (2θ) and
the HMC1512 has sensor output ∆V=V
S
S sin (2θ) for sen-
sor A and sensor B output ∆V
S
=-V
S
S cos (2θ), where V
S
is
supply voltage, S is a constant, determined by materials.
For Honeywell sensors, S is typically 12mV/V.
PRINCIPLES OF OPERATION
MR SENSOR CIRCUITS
Figure 1
Current
Flow
Permalloy
Thin Film
(NiFe)
Metal Contact
M
Applied
Field
θ
PINOUT DRAWINGS
OUT+ 1
GND 1 2
3
4
•
8 OUT-
7 GND 2
6
5 VBRIDGE
θ
•
8
7
6
5
θ
1
2
3
4
OUT- A
OUT- B
VBRIDGEB
VBRIDGEA
GNDA
GNDB
OUT+ B
OUT+ A
HMC1501
HMC1512
Caution: Do not connect GND or Power to Pin 3,4 &6.
OUT+
A
OUT-
A
VBRIDGE A
GND A
B
r
id
ge
A
R
R
R
R
OUT+
OUT-
VBRIDGE
GND 1
R
R
R
R
GND 2
VBRIDGE BOUT +B
OUT -BGND B
B
r
id
ge
B
R
R
R
R
+ -
∆V
R+∆R
M
M
R-∆R
R+∆R
R-∆R
MM
Applied Field Direction
Vs
I