HMC1051/HMC1052/HMC1053
For operation at normal 3.3 or 5-volt logic levels, a single complementary MOSFET pair can be used in a single ended
circuit shown in Figure 4. Other complementary MOSFET pairs can be used with the caution that the chosen devices
should have less than 0.5 ohms ON resistance and be able to handle the needed supply voltages and set/reset currents.
Note that even a 1Hz rate of set/reset function draws an
average current of less than 2 microamperes.
Vsr
200Ω
Vcc
1µf
+
Magnetic Field Detection
IRF7509(P)
S
-
For simple magnetic field sensing applications such
Magnetic Anomaly Detectors (MADs) and Magnetometers,
a similar circuit to the compass application can be
G
.1µf
D
set/reset
D
implemented using one, two, or three magnetic sensors. In
G
the example circuit in Figure 5, a HMC1051Z sensor bridge
is used with a low voltage capable dual op-amp to detect
sufficient intensity of a magnetic field in a single direction.
Uses of the circuit include ferrous object detection such as
vehicle detection, a “sniffer” for currents in nearby
conductors, and magnetic proximity switching. By using two
or three sensor circuits with HMC1051, HMC1052, or
HMC1053 parts, a more omni-directional sensing pattern
Rset/reset
S
4Ω
IRF7509(N)
Figure 4
Single-Ended Driver
can be implemented. There is nothing special in choosing the resistors for the differential op-amp gain stages other than
having like values (e.g. the two 5kΩ and the 500kΩ resistors) matched at 1% tolerance or better to reject common-mode
interference signals (EMI, RFI). The ratio of the 500kΩ/5kΩ resistors sets the stage gain and can be optimized for a
specific purpose. Typical gain ratios for compass and magnetometer circuits using the HMC105X family, range from 50 to
500. The choice of the 5kΩ value sets impedance loading seen by the sensor bridge network and should be about 4 kilo-
ohms or higher for best voltage transfer or matching. Note that Figure 5 also shows an alternative set/reset strap driver
circuit using two darlington complentary paired BJTs as electronic switches.
U1
Vcc
Vcc
5.0v
.1µf
500k
10kΩ pot
Threshold Set
5.00k
5.00k
-
TLC072
+
U2
output
LED
500k
-
TLC072
Vcc/2
+
HMC1051
10kΩ
Vcc
RLED
* Low ESR Tantalum
200Ω
1µf*
-
+
10kΩ
0.1µf
0.1µf
FMMT717
FMMT617
.1uf
set/reset
offset
set/reset
S
R
Figure 5
Magnetic Field Detector
10kΩ
Alternating or Direct Current Sensing
The HMC105X family sensors can be utilized in a novel way for moderate to high current sensing applications using a
nearby external conductor providing the sensed magnetic field to the bridge. Figure 6 shows a HMC1051Z used as a
current sensor with thermistor element performing a temperature compensation function for greater accuracy over a wide
range of operational temperatures. Selection of the temperature compensation (tempco) resistors used depends on the
thermistor chosen and is dependant on the thermistor’s %/°C shift of resistance. For best op-amp compatibility, the
thermistor resistance should be above about 1000 ohms. The use of a 9-volt alkaline battery supply is not critical to this
application, but permits fairly common operational amplifiers such as the 4558 types to be used. Note that the circuit
must be calibrated based on the final displacement of the sensed conductor to the measuring bridge. Typically, an
optimally oriented measurement conductor can be placed about one centimeter away from the bridge and have
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