feature

Miniature Surface Mount Components

Wide field of view ±6 Gauss

1.0 mV/V/Gaussian sensitivity

Low Power Operation to 1.8V

On-chip set/reset and offset band patent

Product Description

Honeywell HMC1051 , HMC1052 and HMC1053 are high performance magnetoresistive sensors designed on a single chip (HMC1051, HMC1052) or two chips (HMC1053). Advantages of these patented chips include quadrature biaxial sensing (HMC1052), miniaturization for ultra-small surface mount and low cost packaging. Each magnetoresistive sensor is configured to convert the magnetic field difference output voltage as a quaternary Wheatstone bridge. Capable of sensing magnetic fields less than 120 microgauss, these sensors offer a compact, highly sensitive and reliable solution for low magnetic field sensing.

compass

Navigation System

attitude reference

Traffic detection

medical instruments

location sensing

Pin Configuration (The arrow indicates the output voltage after generating the positive set pulse.) Model HMC1051

Basic Equipment Operation

Honeywell's HMC105X magnetoresistive series sensors are used to measure magnetic fields in a Wheatstone bridge device. When powered on the bridge, the sensor converts the direction of the sensitive axis to a differential voltage output. In addition to the bridge circuit, the sensor has two magnetically coupled bands on board; an offset band and a set/reset band. These straps are Honeywell's accident scene adjustment and magnetic domain alignment; eliminating the use of external coils around the sensor. The magnetoresistive sensor is made of a nickel-iron (Permalloy) thin film deposited on a silicon wafer as a resistive strip element. In the presence of a magnetic field, the changing resistive elements of the bridge cause an output voltage across the bridge. These resistive elements are aligned together on a common sensitive axis (indicated by arrows) to provide positive voltage changes in the magnetic field increasing in the sensitive direction. Because the output is only proportional to the one-dimensional axis (anisotropy principle) and its scale. Orders of magnitude, additional sensor bridges located in orthogonal directions allow precise measurement of arbitrary field directions. Sensor combination dual-axis and triple-axis quadrature bridge for applications such as compass and magnetometer. The offset band allows for multiple modes of operation when direct current is passed through. These modes are: 1) for unwanted external magnetic fields, 2) bridge offset null voltage, 3) closed loop magnetic field cancellation, 4) automatic bridge gain calibration. The set/reset band can be pulsed with high currents with the following advantages: 1) enables the sensor to perform high sensitivity measurements, 2) reverses the polarity of the bridge output voltage, and 3) periodically serves to improve linearity, reducing the cross axis effect and temperature effect. Noise Characteristics The noise density of the HMR105X series is about 50nV/sqrt Hz at the 1Hz corner, and drops rapidly below 10nV/sqrt Hz at 5Hz, and begins to accommodate Johnson noise values just below 5nV/sqrt Hz at 50 Hz. The 10Hz noise voltage averages about 1.4 microvolts with a standard deviation of 0.8 microvolts.

Horizontal axis effect

The horizontal axis effect of the HMR105X series is typically specified as ±3% of full scale to 1 Gauss. See about this effect and the null method. Offset Strips Offset strips are metallized helical connections on the sensitive shaft of the sensor element. By design, this strap is common to both bridges and must be present if each bridge requires a different strap. In a triaxial design, the A and B bridges are offset bands that drive all three bridges in series along with the C bridge sharing a common node. Each offset band is nominally measured at 15 ohms and requires 10 mA per Gaussian induced field. This strap can easily withstand the shock of current or push fields through the ±6 Gauss linear measurement range, but designers should take care when you do this. In most applications, not using offset bands can be ignored. Designers can leave one or both strap connections (disconnect and disconnect+) open, or ground a connection node. Do not tie two straps together to avoid short circuits. Fix/Reset Tape The Fix/Reset tape is another helix of metallization coupled to the sensor element's easy axis (perpendicular to the sensitive axis on the sensor chip). Like the offset strap, the set/reset strap passes through a pair of bridging element compacts that maintain the overall die size. Each set/reset strip has a nominal minimum requirement of 3 to 6 ohms for the reset or set pulses with a peak current of 400 mA. With the rare exception, the set/reset band must be used to periodically adjust the best and reliable magnetoresistive element. The set pulse is defined as a positive pulse of current into the S/R+ band connection. The successful result is that the magnetic domains are aligned in the direction of the forward easy axis, so that the sensor bridge polarity is a positive slope, producing a positive voltage on the sensitive axis bridge output connection.

A reset pulse is defined as a negative pulse of current into the S/R+ band connection. The successful result is that the magnetic domains are aligned in the opposite easy-axis direction, so that the sensor bridge polarity is a negative slope, producing a negative voltage across the sensitive axis to bridge the output connection. A reset pulse is usually sent first, followed by a set of pulses a few milliseconds later. By pushing magnetic domains in diametrically opposite directions, any previous magnetic interference could be wiped out entirely by the pulse duet. For simplicity against noise and to be precise, a unipolar pulse circuit can be used (set all or reset all). With these unipolar pulses, several pulses together approach the performance of the set/reset pulse circuit. Figure 1 shows a quick and dirty manual pulse circuit for applying pulsed unipolar to the set/reset band

Application Notes

A low-cost dual-axis compass can be used for very high-accuracy measurements when interfacing with low-accuracy sensors using the HMC105X series of sensors, noise amplifiers, and 12- to 16-bit analog-to-digital converters. For low resolution (3° or higher accuracy) or low resolution cost compass applications, 8 or 10 bit A/D converters can be used for general purpose op amps. Figure 2 shows a typical 2-axis compression application using off-the-shelf components. The basic principle of biaxial compression is to orient the two sensor bridge elements horizontally to the ground. (perpendicular to the gravitational field) and measure the resulting X and Y analog output voltages. With the amplified sensor bridge voltage that can be simultaneously converted (measured) to its digital equivalent, the arctangent y/x can be calculated to derive heading information relative to the sensitive direction of the x-axis.

Set/Reset Circuit Notes

The above set/reset circuit in Figure 1 uses the IRF7507 dual complementary mosfet as shown in Figure 2. Details of its H-bridge drive configuration are shown in Figure 2. This configuration is primarily intended for battery powered applications where the 500mA nominal set/reset pulses are used for best current conditions at low voltages. The 200 ohm resistor trickle charges the storage capacitor to the Vcc level for the 1uf power supply and isolates the battery and MOSFET switching from the high current action of the capacitor. In the normal logic state one totem pole switch holds one node capacitor of 0.1uf low, while the other switch charges the capacitor across from the Vcc node. On the first logic change, the polarity of the capacitor is almost twice Vcc, giving the series set/reset load with enough pulse current. Restoring the logic state flip uses 0.1uf capacitor energy storage to produce second nearly equal but opposite polarity current pulses through the set/reset belt. For operation at normal 3.3 or 5V logic levels, a single complementary MOSFET pair can be used in a single-ended circuit as shown in Figure 4. Other complementary MOSFET pairs are available with note that the device selected has a resistance of 0.5 ohms capable of handling the required supply voltage and set/reset current. Note that even the 1Hz set/reset function rate average current is less than 2µA.

Magnetic field detection

For simple magnetic field sensing applications such as Magnetic Anomaly Detectors (MADs) and Magnetometers Circuits similar to compass applications can be implemented using one, two or three magnetic sensors. In the example circuit in Figure 5, the HMC1051Z sensor bridge and dual op amps supporting low voltage are used to detect a magnetic field of sufficient strength in a single direction. Uses for circuits include ferrous object detection, such as vehicle detection, "sniffers" for current in nearby conductors, and magnetic proximity switches. Using two or three sensor circuits with the HMC1051, HMC1052, or HMC1053 parts enables a more omnidirectional sensing mode implementation. There is nothing special about choosing the resistors for the gain stage of the differential op amp to have the same value (e.g. two 5k: and 500k: resistors) matched to 1% or better tolerance to reject common mode interfering signals (EMI, RFI) . The ratio of 500k/5k resistors sets the stage gain and can be optimized for a specific purpose. Typical gain ratios for compass and magnetometer circuits using HMC105X series ranges are from 50 to 500. The choice of 5k: value sets the impedance load seen by the sensor bridge network and should be around 4k ohms or more for voltage transfer or maximum best match. Note that Figure 5 also shows another option to use two Darlington fully paired BJTs as electronic switches to set/reset the belt drive circuit.

AC or DC induction

The HMC105X series of sensors can be used in medium to high current sensing applications to provide an induced magnetic field to the bridge near external conductors. Figure 6 shows use as a current sensor with a thermistor element, with temperature compensation to improve a wide operating temperature range. The choice of temperature compensation (tempco) resistor used depends on the thermistor chosen and on the percentage/degree Celsius change in the thermistor's resistance. For best op amp compatibility, the thermistor resistance should be greater than about 1000 ohms. The use of 9 volt alkaline battery power is not critical for this application, but allows the use of fairly common op amps like the 4558 type. Note that the circuit must calibrate the bridge based on the measured final displacement of the sense conductor. Typically, optimally oriented measurement conductors can be placed in distance bridges and have AC or DC currents ranging from tens of milliamps to over 20 amps.

Tilt-compensated three-axis linkage

For full triaxial compression, the circuit shown in Figure 7 shows the HMC1051 and HMC1052. Triaxial induction magnetic field. Alternatively, a single HMC1053 can be used in a single sensor assembly design. Also shown is a dual-axis accelerometer with digital (PWM) output to provide pitch and roll (tilt) sensing. Corrects the three-axis magnetic sensor output to tilt-compensated two-axis heading. The accelerometer can be replaced with a fluid 2-axis tilt sensor if desired. For low voltage operation (2.5 to 3.6Vdc) powered by lithium batteries, the setup/reset circuit should be upgraded from a single IRF7507 to a dual IRF7507 implementation (according to Figure 2) allowing the HMC1052 and HMC1051 sensors.

Work cycle with reduced energy consumption

For battery powered and other applications requiring limited energy consumption, the sensor bridge and stand electronics can be "turned off" between magnetic field measurements. The HMC105X series magnetic sensors are very low capacitance (bandwidth >5MHz) sensor bridges that settle quickly, usually electronics can before support. Other energy saving ideas are to minimize the number of set/reset pulses, thus saving energy more than battery life. Figure 8 shows a simple power switch circuit that can be controlled by a microprocessor to cycle (switch) electronics in medium current (<25 mA) applications.

The application circuits here constitute typical uses and interfaces for Honeywell products. Honeywell makes no warranty or liability for customer designed circuits from this description or depiction. Honeywell reserves the right to make changes to improve reliability, function or design. Honeywell disclaims any liability arising out of the application or use of any product or circuit described herein; nor does it imply a license under its patents or the rights of others.