SENSOR PRODUCTS APPLICATIONS Compassing Navigation Systems 1 & 2 Axis Magnetoresistive Microcircuits Attitude Reference Traffic Detection Medical Devices Non-Contact Switch Not actual size HMC1001 / 1002 HMC1021 / 1022 C onfigured as a 4-element wheatstone bridge, these highly sensitive sensors convert magnetic fields to a differential output voltage, capable of sensing magnetic fields as low as 30 µgauss. These MRs offer a small, low cost, high sensitivity and high reliability solution for low field magnetic sensing. FEATURES AND BENEFITS Wide Field Range Field range up to ±6 gauss, (earth’s field = 0.5 gauss) Small Package • Designed for 1- and 2-axis to work together to provide 3-axis (x, y, z) sensing • 1-axis part in an 8-pin SIP or an 8-pin SOIC or a ceramic 8-pin DIP package • 2-axis part in a 16-pin or 20-pin SOIC package Solid State These small devices reduce board assembly costs, improve reliability and ruggedness compared to mechanical fluxgates. On-Chip Coils Patented on-chip set/reset straps to reduce effects of temperature drift, non-linearity errors and loss of signal output due to the presence of high magnetic fields Patented on-chip offset straps for elimination of the effects of hard iron distortion Cost Effective The sensors were specifically designed to be affordable for high volume OEM applications. HMC10XX FAMILY HMC1001/1002 SPECIFICATIONS Characteristic Conditions Min Typ Max Unit Bridge Supply (4) Vbridge referenced to GND 5 10 Volts Bridge Resistance Bridge current = 10mA 600 850 1200 ohm Operating Temperature (4) Ambient -40 85 °C Storage Temperature (4) Ambient, unbiased -55 125 °C Field Range (1) (2) (4) Full scale (FS), total applied field -2 +2 gauss Linearity Error (1) (2) (4) Best fit straight line (at 25° C) 0.1 1 0.5 2 %FS Hysteresis Error (1) (2) (4) 3 sweeps across ±2 gauss @ 25° C 0.05 0.10 %FS Repeatability Error (1) (2) (4) 3 sweeps across ±2 gauss @ 25° C 0.05 0.10 %FS S/R Repeatability (1) S/R Repeatability (2) Output variation after alternate S/R pulses 2 10 100 µV Bridge Offset Offset = (OUT+) - (OUT-), Field=0 gauss after Set pulse, Vbridge=8V -60 -15 30 mV Sensitivity (1) (2) At IOFFSET = ±50mA, Vbridge=8V 2.5 3.2 4.0 mV/V/gauss Noise Density Noise at 1Hz, Vbridge=5V 29 nV/ Resolution Bandwidth=10Hz, Vbridge=5V 27 µgauss Bandwidth Magnetic signal (lower limit = DC) 5 MHz OFFSET Strap Measured from OFFSET+ to OFFSET- OFFSET Strap ΩTempco TA=-40 to 85° C OFFSET Field (4) Field applied in sensitive direction Set/Reset Strap Measured from S/R+ to S/R- Set/Reset Current (2) (3) (4) Current at 0.1% duty cycle, or less Disturbing Field (4) Sensitivity starts to degrade. Use S/R pulse to restore sensitivity. ±1 gauss ±2 gauss 2.5 3.5 3900 46 3.0 Hz ohm ppm/° C 51 56 mA/gauss 1.5 1.8 ohm 3.2 5 Amp 3 gauss TA=-40 to 85° C Vbridge=8V Ibridge=5mA -3000 -600 ppm/° C Bridge Offset Tempco TA=-40 to 85° C Ibridge=5mA no Set/Reset with Set/Reset ±300 ±10 ppm/° C Resistance Tempco Vbridge=8V, -40 to 85° C 2500 ppm/° C Cross-Axis Effect Cross field=1gauss (see AN-205) ±3 +0.5 %FS Max. Exposed Field (4) No perming effect on zero reading Weight HMC1001 HMC1002 Sensitivity Tempco no Set/Reset with Set/Reset 100 0.14 0.53 (1) VBridge = 4.3V, IS/R = 3.2A, T = 25°C. VOUT = VSET - VRESET (2) If VBridge = 8.0V, IS/R = 2.0A, T = 25°C, lower S/R current leads to greater output variation. (3) Effective current from power supply is less that 1mA. (4) Not tested, guaranteed by characterization. Units: 1 gauss (g) = 1 Øersted (in air), = 79.58 A/m, 1G = 10E-4 Tesla, 1G = 10E5 gamma. 2 gauss gram HMC10XX FAMILY HMC1021/1022 SPECIFICATIONS Characteristic Conditions Min Typ Max Unit Bridge Supply Vbridge referenced to GND 3 5 12 Volts Bridge Resistance Bridge current = 5mA 80 0 1100 1300 Ω Operating Temperature Ambient -40 85 °C Storage Temperature Ambient, unbiased -55 125 °C Field Range Full scale (FS) — total applied field -6 +6 gauss Linearity Error Best fit straight line (at 25° C) Hysteresis Error 0.05 0.4 1.6 %FS 3 sweeps across ±3 gauss @ 25° C 0.08 %FS Repeatability Error 3 sweeps across ±3 gauss @ 25° C 0.08 %FS Gain Error Applied field for zero reading 0.05 0.10 %FS Bridge Offset Offset = (OUT+) - (OUT-), Field=0 gauss after Set pulse, Vbridge=5V -10 ±2.5 +10 mV Sensitivity At Vbridge=5V 0.8 1.0 1.2 mV/V/gauss Noise Density Noise at 1Hz, Vbridge=5V 48 nV/√Hz Resolution Bandwidth=10Hz, Vbridge=5V 85 µgauss Bandwidth Magnetic signal (lower limit = DC) 5 MHz OFFSET Strap Measured from OFFSET+ to OFFSET- OFFSET Strap ΩTempco TA=-40 to 85° C OFFSET Field Field applied in sensitive direction Set/Reset Strap Measured from S/R+ to S/R- Set/Reset Current Disturbing Field ±1 gauss ±3 gauss ±6 gauss 50 60 3900 Ω ppm/° C 4.0 4.6 6.0 mA/gauss 6 7.7 9 Ω Current at 0.1% duty cycle, or less 0.5 0.5 4.0 Amp Sensitivity starts to degrade. Use S/R pulse to restore sensitivity. 20 TA=-40 to 85° C Vbridge=5V Ibridge=5mA Bridge Offset Tempco TA=-40 to 85° C Ibridge=5mA no Set/Reset with Set/Reset Resistance Tempco Sensitivity Tempco 40 -2800 gauss -3000 -600 -3200 ppm/° C ±500 ±10 ppm/° C Vbridge=5V, -40 to 85° C 2500 ppm/° C Cross-Axis Effect Cross field=1gauss (see AN-205) +0.3 %FS Max. Exposed Field No perming effect on zero reading 200 gauss Set/Reset (1) S/R current > 0.5 Amps 30 µV (1) Not tested, guaranteed by design. Happlied=±1 gauss Units: 1 gauss (G) = 1 Oersted (in air), 1G = 79.58 A/m, 1G = 10E-4 Tesla, 1G = 10E5 gamma 3 HMC10XX FAMILY KEY PERFORMANCE DATA Sensor output vs magnetic field Output is repeatable in field range ±20 Oe Sensor output vs magnetic field after being set or reset 15 60 1021/1022 1021/1022 10 40 Voltage Output (mV) Output Voltage (mV) Vb=5V 5 0 Reset -5 Set -10 Vb=5V 20 0 -20 2 sweeps 2 sweeps -40 -15 -60 -20 -2 -1 0 1 -20 2 -15 -10 -5 0 5 Sensitivity vs temperature Constant voltage power supply 15 20 Sensor noise vs frequency 1.3 1000 1021/1022 1021/1022 1.2 Vb=5V Vb=5V Sensitivity (mV/V/Oe) Noise Density (nV/rt Hz) 10 Field (Oe) Field (Oe) 100 10 1.1 1 0.9 0.8 0.7 0.6 1 0.1 1 10 100 -50 1000 -25 0 Frequency (Hz) 25 50 75 100 125 Temperature (C) Effects of set/reset pulse variation 2µ sec pulse duration, S/R voltage >4V is recommended Bridge resistance vs temperature 1400 1 Vb=5V 1021/1022 All types 0.8 Vb=5V Nonrepeatability Resistance (ohm) 1300 1200 1100 Null Voltage (mV) (Set) Sensitivity (mV/V/Oe) (Set) 0.4 0.2 900 0 -25 0 25 50 75 100 Sensitivity (mV/V/Oe) (Reset) no set/reset in this region 1000 -50 Null Voltage (mV) (Reset) 0.6 0 125 Temperature (C) 1 2 3 Set/Reset Voltage (V) 4 4 5 HMC10XX FAMILY PACKAGE / PINOUT SPECIFICATIONS HMC1001—One Axis MR Microcircuit HMC1002—Two-Axis MR Microcircuit GND1 (A) 1 20 S/R- (A) OUT+ (A) 2 Die A OFFSET- (A) 3 Vbridge (A) 4 18 GND PLN 17 OFFSET (+A) OUT- (A) 5 16 S/R+ (A) GND2 (A) 6 Die B S/R- (B) 7 15 OFFSET+ (B) 14 S/R+ (B) GND1 (B) 8 13 GND2 (B) Out+ (B) 9 12 OUT- (B) OFFSET- (B) 10 11 Vbridge (B) HMC1022—Two-Axis MR Circuit OFFSET- (A) OUT+ (A) VBRIDGE (A) OUT- (A) OUT- (B) VBRIDGE (B) GND (A) S/R+ (B) 1 2 3 4 5 6 7 8 •Die A 16 15 14 13 12 11 10 9 Die B 1 2 3 4 Die 8 7 6 5 Die HMC1021S—One-Axis MR Circuit OFFSET+ (A) S/R- (A) S/R+ (A) GND (B) OUT+ (B) OFFSET- (B) OFFSET+ (B) S/R- (B) OUT+ VBRIDGE GND OUT- 1 2 3 4 • Die 8 7 6 5 OFFSETOFFSET+ S/RS/R+ HMC1021S HMC1021D—One-Axis MR Circuit OUT+ VBRIDGE GND OUT- • S/R+ 1 OFFSET+ 2 S/R- 3 GND 4 Out+ 5 OFFSET- 6 Vbridge 7 Out- 8 19 NC HMC1021Z—One-Axis MR Circuit OUTVBRIDGE S/R+ GND S/ROFFSET+ OFFSETOUT+ OFFSETOFFSET+ S/RS/R+ 1 2 3 4 5 6 7 8 Arrow indicates direction of applied field that generates a positive output voltage after a SET pulse. 5 • Die HMC10XX FAMILY BASIC DEVICE OPERATION The OFFSET strap allows for several modes of operation when a dc current is driven through it. Honeywell magnetoresistive sensors are simple resistive bridge devices (Figure 1) that only require a supply voltage to measure magnetic fields. When a voltage from 0 to 10 volts is connected to Vbridge, the sensor begins measuring any ambient, or applied, magnetic field in the sensitive axis. In addition to the bridge circuit, the transducer has two onchip magnetically coupled straps—the OFFSET strap and the Set/Reset strap. These straps are patented by Honeywell and eliminate the need for external coils around the devices. Vbridge (7) R OFFSET + (2) R 3.5 Ω max. • An unwanted magnetic field can be subtracted out • The bridge offset can be set to zero • The bridge output can drive the OFFSET strap to cancel out the field being measured in a closed loop configuration • The bridge gain can be auto-calibrated in the system on command. The Set/Reset (S/R) strap can be pulsed with a high current to: OFFSET (6) • Force the sensor to operate in the high sensitivity mode • Flip the polarity of the output response curve • Be cycled during normal operation to improve linearity and reduce cross-axis effects and temperature effects. Ioffset R=600-1200 Ω OUT(8) R R 2.0 Ω max. S/R + (1) S/R (3) Iset, -Ireset GND (4) The output response curves shown in Figure 2 illustrate the effects of the S/R pulse. When a SET current pulse (Iset) is driven into the SR+ pin, the output response follow the curve with the positive slope. When a RESET current pulse (Ireset) is driven into the SR- pin, the output response follow the curve with the negative slope. These curves are mirror images about the origin except for two offset effects. Figure 1—On-Chip components (HMC1001) Magnetoresistive sensors are made of a nickel-iron (Permalloy) thin film deposited on a silicon wafer and patterned as a resistive strip. In the presence of an applied magnetic field, a change in the bridge resistance causes a corresponding change in voltage output. In the vertical direction, the bridge offset shown in Figure 2, is around -25mV. This is due to the resistor mismatch during the manufacture process. This offset can be trimmed to zero by one of several techniques. The most straight forward technique is to add a shunt (parallel) resistor across one leg of the bridge to force both outputs to the same voltage. This must be done in a zero magnetic field environment, usually in a zero gauss chamber. An external magnetic field applied normal to the side of the film causes the magnetization vector to rotate and change angle. This in turn will cause the resistance value to vary (∆R/ R) and produce a voltage output change in the Wheatstone bridge. This change in the Permalloy resistance is termed the magnetoresistive effect and is directly related to the angle of the current flow and the magnetization vector. The offset of Figure 2 in the horizontal direction is referred to here as the external offset. This may be due to a nearby ferrous object or an unwanted magnetic field that is interfering with the applied field being measured. A dc current in the OFFSET strap can adjust this offset to zero. Other methods such as shielding the unwanted field can also be used to zero the external offset. The output response curves due to the SET and RESET pulses are reflected about these two offsets. During manufacture, the easy axis (preferred direction of magnetic field) is set to one direction along the length of the film. This allows the maximum change in resistance for an applied field within the permalloy film. However, the influence of a strong magnetic field (more than 10 gauss) along the easy axis could upset, or flip, the polarity of film magnetization, thus changing the sensor characteristics. Following such an upset field, a strong restoring magnetic field must be applied momentarily to restore, or set, the sensor characteristics. This effect will be referred to as applying a set pulse or reset pulse. Polarity of the bridge output signal depends upon the direction of this internal film magnetization and is symmetric about the zero field output. 40 Vcc=8V Output Voltage (mV) 20 (1001/1002) response after Iset response after Ireset 0 bridge offset -20 -40 external offset -60 1.50 1.25 1.00 0.75 0.50 0.25 0.00 -0.25 -0.50 -0.75 -1.00 -1.50 -80 -1.25 OUT+ (5) Applied Field (Gauss) Figure 2—Output Voltage vs. Applied Magnetic Field 6 HMC10XX FAMILY WHAT IS OFFSET STRAP? Any ambient magnetic field can be canceled by driving a defined current through the OFFSET strap. This is useful for eliminating the effects of stray hard iron distortion of the earth’s magnetic field. For example, reducing the effects of a car body on the earth’s magnetic field in an automotive compass application. If the MR sensor has a fixed position within the automobile, the effect of the car on the earth’s magnetic field can be approximated as a shift, or offset, in this field. If this shift in the earth's field can be determined, then it can be compensated for by applying an equal and opposite field using the OFFSET strap. Another use for the OFFSET strap would be to drive a current through the strap that will exactly cancel out the field being measured. This is called a closed loop configuration where the current feedback signal is a direct measure of the applied field. in field the MR sensor measures—call that the delta applied field (∆Ha). The MR sensor gain is then computed as: MRgain = (H2-H1) / ∆Ha There are many other uses for the OFFSET strap than those described here. The key point is that ambient field and the OFFSET field simply add to one another and are measured by the MR sensor as a single field. NOISE CHARACTERISTICS The noise density curve for a typical MR sensor is shown in Figure 3. The 1/f slope has a corner frequency near 10 Hz and flattens out to 3.8 nV/√Hz. This is approximately equivalent to the Johnson noise (or white noise) for an 850Ω resistor—the typical bridge resistance. To relate the noise density voltage in Figure 3 to the magnetic fields, use the following expressions: The field offset strap (OFFSET+ and OFFSET-) will generate a magnetic field in the same direction as the applied field being measured. This strap provides a 1 Oersted (Oe) field per 50 mA of current through it. (Note: 1 gauss=1 Oersted in air). That is, if 25 mA were driven from the OFFSET+ pin to the OFFSET- pin, a field of 0.5 gauss would be added to any ambient field being measured. Also, a current of -25 mA would subtract 0.5 gauss from the ambient field. The OFFSET strap looks like as a nominal 2.5 ohm resistance between the OFFSET+ and OFFSET- pins. For Vsupply=5V and Sensitivity=3.2mV/V/gauss, Bridge output response = 16 mV/gauss or 16 nV/µgauss The noise density at 1Hz ≈ 30nV/√Hz and corresponds to 1.8 µgauss/√Hz The OFFSET strap can be used as a feedback element in a closed loop circuit. Using the OFFSET strap in a current feedback loop can produce desirable results for measuring magnetic fields. To do this, connect the output of the bridge amplifier to a current source that drives the OFFSET strap. Using high gain and negative feedback in the loop, this will drive the MR bridge output to zero, (OUT+) = (OUT-). This method gives extremely good linearity and temperature characteristics. The idea here is to always operate the MR bridge in the balanced resistance mode. That is, no matter what magnetic field is being measured, the current through the OFFSET strap will cancel it out. The bridge always “sees” a zero field condition. The resultant current used to cancel the applied field is a direct measure of that field strength and can be translated into the field value. For the noise components, use the following expressions: 30 * √(ln(10/.1)) nV 64 nV (rms) 4 µgauss (rms) 27 µgauss (p-p) 1/f noise(0.1-10Hz) = white noise (BW=1KHz) = 3.8 * √BW nV 120 nV (rms) 50 µgauss (p-p) 1000 (1001/1002) 100 Noise Density (nV/ √ Hz) The OFFSET strap can also be used to auto-calibrate the MR bridge while in the application during normal operation. This is useful for occasionally checking the bridge gain for that axis or to make adjustments over a large temperature swing. This can be done during power-up or anytime during normal operation. The concept is simple; take two point along a line and determine the slope of that line—the gain. When the bridge is measuring a steady applied magnetic field the output will remain constant. Record the reading for the steady field and call it H1. Now apply a known current through the OFFSET strap and record that reading as H2. The current through the OFFSET strap will cause a change 10 1 0.1 1 10 Frequency 100 (Hz) Figure 3—Typical Noise Density Curve 7 1000 HMC10XX FAMILY WHAT IS SET/RESET STRAP? There are many ways to design the set/reset pulsing circuit, though, budgets and ultimate field resolution will determine which approach will be best for a given application. A simple set/reset circuit is shown in Figure 4. Most low field magnetic sensors will be affected by large magnetic disturbing fields (>4 gauss) that may lead to output signal degradation. In order to reduce this effect, and maximize the signal output, a magnetic switching technique can be applied to the MR bridge that eliminates the effect of past magnetic history. The purpose of the Set/ Reset (S/R) strap is to restore the MR sensor to its high sensitivity state for measuring magnetic fields. This is done by pulsing a large current through the S/R strap. The Set/ Reset (S/R) strap looks like a resistance between the SR+ and SR- pins. This strap differs from the OFFSET strap in that it is magnetically coupled to the MR sensor in the crossaxis, or insensitive, direction. Once the sensor is set (or reset), low noise and high sensitivity field measurement can occur. In the discussion that follows, the term “set” refers to either a set or reset current. 6-9V 3 IRF7105 25K 0.2µF S/R+ S/R- 4 RESET SET RESET Signal should be in RESET state when idle 0.1µF 5,6 7,8 2 1 Signal input 5V Manual Switch Figure 4—Single-Axis Set/Reset Pulse Circuit (1001) The on-chip S/R should be pulsed with a current to realign, or “flip”, the magnetic domains in the transducer. This pulse can be as short as two microsecond and on average consumes less than 1 mA dc when pulsing continuously. The duty cycle can be selected for a 2 µsec pulse every 50 msec, or longer, to conserve power. The only requirement is that each pulse only drive in one direction. That is, if a +3.5 amp pulse is used to “set” the sensor, the pulse decay should not drop below zero current. Any undershoot of the current pulse will tend to “un-set” the sensor and the sensitivity will not be optimum. The magnitude of the set/reset current pulse depends on the magnetic noise sensitivity of the system. If the minimum detectable field for a given application is roughly 500 µgauss, then a 3 amp pulse (min) is adequate. If the minimum detectable field is less than 100 µgauss, then a 4 amp pulse (min) is required. The set/reset straps on the Honeywell magnetic sensors are labeled S/R+ and S/R-. There is no polarity implied since this is simply a metal strap resistance of typically 1.5Ω per sensor. Therefore, for a three axis system, the total series strap resistance is typically 4.5Ω. Using the S/R strap, many effects can be eliminated or reduced that include: temperature drift, non-linearity errors, cross-axis effects, and loss of signal output due to the presence of a high magnetic fields. This can be accomplished by the following process: If three axis are used, it is recommended that the straps are connected in series to insure the same current pulse flows through all three sensors. Assuming the pulse drive circuitry has a source impedance of 0.5Ω, the set/reset current pulse will effectively drive a 5Ω load. Now to generate a 3-4 amp minimum pulse into a 5Ω load requires a 15-20V supply. • A current pulse, Iset, can be driven from the S/R+ to the S/R- pins to perform a “SET” condition. The bridge output can then be measured and stored as Vout(set). • Another pulse of equal and opposite current should be driven through the S/R pins to perform a "RESET" condition. The bridge output can then be measured and stored as Vout(reset). • The bridge output, Vout, can be expressed as: Vout = [Vout(set) - Vout(reset)]/2. This technique cancels out offset and temperature effects introduced by the electronics as well as the bridge temperature drift. The magnitude of the S/R current pulse depends on the magnetic noise sensitivity of the application. If the minimum detectable field for a given application is roughly 500 µgauss, then a 2.5 amp pulse (min) is adequate. If the minimum detectable field is less than 100 µgauss, then a 3.5 amp pulse (min) is required. The circuit that generates the S/R pulse should be located close to the MR sensor and have good power and ground connections. 8 HMC10XX FAMILY SET and RESET signals are generated from a microprocessor and control the P and N channel HEXFET drivers (IRF7106). The purpose of creating the TRS and the TSR delays are to make sure that one HEXFET is off before the other one turns on. Basically, a break-before-make switching pattern. The current pulse is drawn from the 4.7 µF capacitor. If the 5V to 20V converter is used as shown in Figure 6, then the resultant noise and droop on the 16-20V supply is not an issue. But if the 16-20V supply is used elsewhere in the system, then a series dropping resistor (≈500Ω) should be placed between the 4.7µF capacitor and the supply.time constant. That is, the minimum high and low time for Clock is ≈25 µs. Single Clock Circuitry—Some form of clock is needed to trigger the set and reset pulses (Figure 5) to create the switching signal. The circuit shown in Figure 7 can be used to create a strong (>4Amp) pulse. The diodes, resistors, capacitors and inverters basically create the TRS and the TSR delays. Now a single signal (Clock) can trigger a set or reset pulse. The minimum timing between the rising and falling edges of Clock are determined by the 25KΩ and 1nF time constant. That is, the minimum high and low time for Clock is ≈25 µs. Micro Processor—The circuit in Figure 8 generates a strong set/reset pulse (>4 Amp) under microprocessor control. The MAX662A 5V 2 Clock C1+ C2- C1- C2+ 3 0.22µF* 0.22µF* 1 16V set 8 TPW ≈ 2 µsec 1µF SHDN GND 7 Vout S/R 5V -16V 5 reset 4 20V 6 1N5818 Vcc 2µF 1µF 12V 1µF Figure 5—Single Clock Set/Reset Timing * Use tantalum capacitors Figure 6—5V to 20V Converter +16 to 20V 4.7µF (3) 5V 9 8 25K 74HC04 25K 3 25K 3 4 IRF7106 (1) Clock 14 4 7 1N4001 1nF 25K 1 2 5 6 0.1µF 10K S/R strap @ 4.5Ω typ. 3A peak (min.) HMC2003 1 17 0.22µF (2) 5,6 7,8 2N3904 2 S/R 1 1nF (1) HEXFETs with ≈0.2Ω Ron (2) 0.22µF Tantalum or a 0.68 µF Ceramic CK06 (3) Tantalum, low R Figure 7—Single Clock Set/Reset Pulse Circuit (1001/1002) +16 to 20V 5V 4.7µF (1) SET 25K 25K TRS 3 TSR IRF7106 (2) RESET 4 16V set 10K 0.1µF SET S/R TRS ≥ 5 µsec TSR ≥ 5 µsec TPW ≈ 2 µsec -16V reset HMC2003 17 0.22µF 1 5,6 7,8 2N3904 TPW S/R strap @ 4.5Ω typ. 3A peak (min.) 2 RESET S/R 1 (1) Tantalum, low R (2) HEXFETs with ≈0.2Ω Ron Figure 8—Set/Reset Circuit With Microprocessor Control(1001/1002) 9 HMC10XX FAMILY Low Field Measurements—When measuring 100 µgauss resolution or less, the permalloy film must be completely set, or reset, to insure low noise and repeatable measurements. A current pulse of 4 amps, or more, for just a couple microseconds will ensure this. The circuits in Figures 7 and 8 are recommended for applications that require low noise and high sensitivity magnetic readings. For any magnetic sensor application, if temperature drift is not an issue, then the reset pulse need only be occasionally applied. This will save power and enable the use of digital filtering techniques as shown in Figure 11. Circumstances for a reset pulse would be 1) power on or, 2) field over/ under range condition. Any other time the sensor should perform normally. Low Cost—For minimum field measurements above 500 µgauss, a less elaborate pulsing circuit can be used. In both Figures 9 and 10, the pulse signal is switched using lower cost Darlington transistors and fewer components. This circuit may have a more limited temperature range depending on the quality of transistors selected. If accuracy is not an issue and cost is, then the reset only circuit in Figure 10 will work. 200 1µF (1) +5V 10K 0.1µF HMC1022 FMMT717 14 8 9,15 0.1µF 0.1µF +16 to 20V Clock 4.7µF (1) 10K S/R strap @ 4.5Ω typ. 3A peak (min.) 0.022µF FMMT617 10K (1) Tantalum, low R ZTX705 HMC2003 17 0.22µF Figure 11—5V Circuit for SET/RESET (1021/1022) 1 0.022µF Clock ZTX605 The circuit in Figure 12 generates a strong set/reset pulse under a microprocessor clock driven control. A free running 555 timer can also be used to clock the circuit. The SET current pulse is drawn from the 4.7µF capacitor and a 200 ohm dropping resistor should be placed in series with the supply to reduce noise. S/R 10K (1) Tantalum, low R Figure 9—Single Clock Set/Reset Circuit(1001/1002) S/R strap @ 4.5Ω typ. 3A peak (min.) +16 to 20V 100K HMC2003 0.22µF 17 1 0.022µF Clock ZTX605 S/R 10K 5V Clock S/R TPW ≈ 2 µsec -16V reset Figure 10—Single Clock Reset Only Circuit (1001/1002) 10 HMC10XX FAMILY 200 1µF (1) +5 to 15V 5V 3 Clock 4 4 to14V TPW ~ 2 µsec S/R HMC1022 IRF7105 (2) DI9952 (2) set 14 8 9,15 0.1µF reset Clock -4 to -14V set 5,6 7,8 2 rst set S/R 1 (1) Tantalum, low R (2) Rds ~0.2 ohm Figure 12—Set/Reset Pulse With Clock Control(1021/1022) Low Power—For low power application, down to 3.3 volt supply, the circuit shown in Figure 14 can be used. These low threshold FETs provide low on-resistance (0.3W) at VGS=2.7V. The set/reset pulsing does not need to be continuous. To save power, the SET pulse can be initially applied followed by a single RESET pulse. The offset (OS) can be calculated as: SET Pulse Read Vset RESET Pulse Read Vrst OS = (Vset + Vrst)/2 OS = (Vset+Vrst)/2 This offset term will contain the DC offset of both the sensor bridge and interface electronics, as well as the temperature drift of the bridge and interface electronics. Store this value and subtract it from all future bridge output readings. Once the bridge is RESET, it will remain in that state for years— or until a disturbing field (>20 gauss) is applied. A timer can be set, say every 10 minutes, to periodically update the offset term. A flow chart is shown in Figure 13 along with a timing diagram in Figure 14 to illustrate this process. Ta Tb Ta Vout = Vrst - OS Timer expired? n Read Vrst Figure 13—Low Power Set/Rst Flowchart Tc 200 Reset +3.3 to 6.5V Set 1,3 Td Td read Vrst read Vset Vout Vp Set + HMC1022 14 NDS9933 8 9,15 0.1µF 5,6,7,8 Reset TPW Ta > 5 µsec Tb > 1 µsec Tc > 20 µsec, 50 msec(max) Td > 20 µsec 1µF (1) 2,4 5,6,7,8 set S/R y -Vp 2,4 S/R 1,3 reset (1) Tantalum, low R (2) Rds ~0.2 ohm NDS8926 TPW ~ 2 µsec Vp > 3 V Figure 14—Single Clock Set/Reset Pulse Circuit (1021/1022) 11 HMC10XX FAMILY Simple Circuit Application 30mV. The magnet must be strong (200 gauss) and have one of its magnetic poles point along the sensitive direction of the sensor. This circuit can be used to detect a door open/ closed status or the presence or absence of an item. Figures 16, 17 and 18 show other circuit examples. The circuit in Figure 15 shows a simple magnetic sensor. This circuit acts as a proximity sensor and will turn on the LED when a magnet is brought within 0.25 to 0.5 inch of the sensor. The amplifier acts as a simple comparator and switches low when the HMC1001 bridge output exceeds Magnetic Sensor +5V +5V 7 0.15µF# 7 HMC1001 magnet movement 100 1 8 V+ V- 5 + AMP04 - 2 R1* LED 400 8 3 6 Vout 5 4 Gain=1000, BW=10Hz * R1 is used to trim switchpoint # provides 10Hz rolloff 4 Calibrate: 1. Trim R1 for (+V) - (-V) < 30mV 2. Apply signal < 30mV, LED should be off. 3. Apply signal > 30mV, LED should be on. Figure 15—Magnetic Proximity Switch Magnetic Sensor 650 V+ 7 HMC1001 +5V R1* 8 2 5 3 8 + 7 Ain+ 8 AMP04 5 Ain- V+ 25K 1.6Ω 3 Vout 6 Vref 10 LM440 2.5V 1 9 12 V+ CONV SCLK Ref+ SDATA NDRDY XIN RefGnd CAL NCS 6,11,13 +5V 2 14 15 16 4 3 Serial Bus Interface R2* 4 CS5509 16 bit A/D 1.5nF# 1 1 * R1 or R2 used to trim offest # provides 1KHz rolloff S/R Pulse Figure 16—One-Axis Sensor With Digital Interface BS250 +6-15V 100K Magnetic Sensor 4 10 3 CS5509 16 bit A/D R1* 8 5 mA 2 3 5 R2* 4 1 8 + Ain+ Ain- V+ 25K LM440 2.5V 1 S/R Pulse 7 8 AMP04 5 1.6Ω 3 Vout 6 Vref 9 10 12 Ref+ RefGnd V+ CONV SCLK SDATA NDRDY XIN CAL NCS 6,11,13 2 +5V 14 15 16 4 3 Serial Bus Interface R3** + - 22.1K LMC7101 650 1.5nF# HMC1001 1 Vref V+ 7 0.01 1 * R1 or R2 used to trim offest **R3 = 451Ω for 1 axis, 921Ω for 2 axis, or 1411Ω for 3 axis # provides 1KHz rolloff Figure 17—One-Axis Sensor With Constant Bridge Current and Digital Interface 12 HMC10XX FAMILY Magnetic SensorS V+ 4 +5V 5 X 650 2 3 2 TLC2543 12 bit A/D 8 + 6 1 AMP04 2 5 Vref HMC1002 V+ 11 650 R3* Y 2 12 3 1.5nF# 10 AIN1 DOUT NCS EOC Ref+ RefGnd 20 +5V 18 17 16 15 19 8 + R4* 8,13 13 1 9 6 +5V AMP04 5 25K Vref 20 14 LM440 2.5V 1.6 1.6 7,18 16 MAX662A * R1-R4 used to trim offest # provides 1KHz rolloff 0.22µF + 1K 4 + 25K 3 0.2µF 3 12V 4.7µF tantalum IRF7105 +5V 14 V+ CLK DIN AIN0 Serial Bus Interface R2* 1,6 1.5nF# 1 R1* 4.7µF 6 C2C2+ Vout C1+ C1Vcc SHDN GND 4 2 + 1 0.22µF 5 +5V 8 4.7µF 7 0.1µF 0.1µF 5,6 7,8 2 SR Signal input 5V Manual Switch 1 Rst Set Rst Signal should be in Rst state when idle Figure 18—Two-Axis Sensor With Set/Reset Circuit and Digital Interface 13 HMC10XX FAMILY PACKAGE OUTLINES HMC1002—Package Outline A1 D 20 11 E 1 H 10 Millimeters Inches Symbol A A1 B D E e H h Max Min 2.642 2.489 0.279 0.127 0.483 0.457 12.675 12.929 7.417 7.264 1.270 ref 1.270 10.566 ref 0.381 Max Min .104 .098 .011 .005 .019 .014 .509 .499 .292 .286 .050 refref .416 .396 .030 .015 Millimeters Inches Symbol A A1 B D E e H h Max Min 1.728 1.371 0.249 0.101 0.483 0.355 9.829 11.253 3.988 3.810 1.270 ref 5.314 5.014 0.762 0.381 Max Min .068 .054 .010 .004 .019 .014 .443 .387 .157 .150 .050 ref .209 .197 .030 .015 Symbol A A1 b D E E1 e Q L Min h A e B HMC1001—8-Pin SIP and HMC1021Z—8-Pin SIP D H E h x 45° 1 8 • A A1 B e HMC1021D—8-Pin Ceramic DIP A1 D 8 7 6 E1 E 1 Q 2 3 Millimeters 5 4 A L e b Max Inches Max Min 0.107 ref 0.012 0.009 0.020 0.016 0.405 — 0.298 0.282 0.310 0.290 0.100 ref 0.060 0.015 0.175 0.125 HMC1021S 8-Pin SOIC D A1 A H E 1 • e B h x 45° Millimeters Inches Symbol A A1 B D E e H h Min Max 1.371 1.728 0.101 0.249 0.355 0.483 4.800 4.979 3.810 3.988 1.270 ref 5.816 6.198 0.381 0.762 Max Min .068 .054 .010 .004 .019 .014 .196 .189 .157 .150 .050 ref .244 .229 .030 .015 Symbol A A1 B D E e H h Millimeters Max Min 1.728 1.371 0.249 0.101 0.483 0.355 11.253 9.829 3.988 3.810 1.270 ref 6.198 5.816 0.762 0.381 Inches Max Min .068 .054 .010 .004 .019 .014 .443 .387 .157 .150 .050 ref .244 .229 .030 .015 HMC1022 16-Pin SOIC D H E A1 16 9 1 8 • e B A h x 45° 14 HMC10XX FAMILY DESIGN / PACKAGE OPTIONS Two-axis parts contain two sensors for the x- and y- field measurements. Single-axis variations include a SIP package for mounting through the circuit board to create a 3-axis solution, a SOIC for direct surface mount, and a ceramic DIP for high performance military and high temperature applications. Honeywell offers a range of magnetic microcircuit products. Two different sensor designs and five package configurations are available: • HMC1001/1002 series offers a higher sensitivity and lower field resolution. • HMC1021/1022 series offers a wider field range, lower set/reset current and has a lower cost for higher volume applications. HMC1001/02 HMC1021/22 Units Sensitivity 3.1 1.0 mV/V/G Resolution 40 85 µgauss Range ±2 0.5 gauss Set/Rst Current 3.0 0.5 Amps Cost Lower in high volume ORDERING INFORMATION Part Number Axis Number Sensitivity Package Style HMC1001 Single 3mV/V/G 8-Pin SIP HMC1002 Two 3mV/V/G 20-Pin SOIC HMC1021D Single 1mV/V/G 8-Pin Ceramic DIP HMC1021Z Single 1mV/V/G 8-Pin SIP HMC1021S Single 1mV/V/G 8-Pin SOIC Two 1mV/V/G 16-Pin SOIC HMC1022 Solid State Electronics Center • 12001 State Highway 55, Plymouth, MN 55441 • (800) 238-1502 • www.magneticsensors.com Additional Product Details: Customer Service Representative (612) 954-2888 fax: (612) 954-2257 E-Mail: [email protected] Honeywell reserves the right to make changes to any products or technology herein to improve reliability, function or design. Honeywell does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. 900248 5-99 15