Application Note 20 Issue 1 April 1996 Magnetoresistive Sensors Principles of Operation and Applications Stefan Hübschmann Matthias Schneider This a pplication note provides an overview of the Zetex range of Magnetoresistive sensors. The layout of a typical magnetoresistive chip (parent device 174B) is shown in Figure 1, and is for example the chip used in the ZMY20 sensor. Thin film stripes are a characteristic feature of a magnetoresistive chip. These stripes are made by photolithography and consist of Permalloy (Ni81Fe19), a magnetic material evaporated on an oxidised silicon wafer. The electrical resistivity of the stripes is changed by a magnetic field Hy due to the magnetoresistive effect. The field Hy causes a rotation of Figure 1 Magnetoresistive Magnetic Field Sensor, (Parent Device 174B). the magnetisation in the stripe. This is shown in Figure 2. The resistivity R of a permalloy stripe depends on the angle betwe en the directions of electric current (I) and magnetisation (M): R = Ro + ∆Ro cos2α where ∆R0 describes the strength of the magnetoresistive effect. T h e m a x i m u m r e l a t iv e cha n g e o f resistivity ∆R0/R is approximately 2 to 3% for permalloy. The relationship between an external field Hy and angle α is Figure 2 The magnetoresistive effect depends on the angle between the direction of electric current (I) and magnetisation (M). A rotation of the magnetisation in a permalloy stripe takes place when a magnetic field in the y-direction is applied. Without an external field the magnetisation is along the x-direction due the shape of the stripe. AN20 - 1 Application Note 20 Issue 1 April 1996 Application Note 20 Issue 1 April 1996 determined by the geometrical di m e n s io ns of the s tri pe and the magnetic anisotropy of permalloy. This is taken into account by introducing a f i e l d H0 t h a t r e p r e s e n t s t h e demagnetising and anisotropic field. One obtains sin2 α = Hy2 H02 sin2 α = 1 Figure 3 Covering the stripe with “Barber poles” consisting of aluminium changes the direction of the current. This does not influence the direction of magnetisation. for H < H0 for H > H0 The characteristic of a magnetoresistive stripe as a field sensor is: Hy 2 R = R0 + ∆R0 1− 2 H0 for H < H0 A linear characteristic of the magnetoresistive sensor is required to measure a small magnetic field. The linear behaviour of the magnetoresistive sensor is achieved by using a “Barber pole” geometry. The stripes in Figure 1 are covered with aluminium bars having an inclination of 45° to the stripe axis. Aluminum has a low resistivity compared to permalloy. Therefore the Barber poles cause a change of the current direction. The angle between current and magnetisation is shifted by 45° as shown in Figure 3. The relationship between resistance and magnetic field is now Hy R =Ro + ∆R0 ± ∆Ro 2 Ho H √ 1− H y 0 The stripes of the magnetoresistive chip are arranged as a meandering pattern. They form a Wheatstone bridge which is shown schematically in Figure 5. The applied voltage is Vb. Each half bridge consists of two resistors with different “Barber pole” orientations. The voltage between the resistors of a half bridge changes upon application of a magnetic field. R R0+∆R0 with Barber poles without Barber poles R0 2 -1 2 A linear characteristic of the sensor is given around Hy2/H20 = 0. The sign in this equation is determined by the inclination of the “Barber poles” (±45°) Figure 6 Safe operating area of ZMY20/ZMZ20. Hxtot=Hx + Hd ; Tamb = 25°C Hd = disturbing field. to the stripe axis. The characteristic of a sensor with and without Barber poles is presented in Figure 4. -0,5 0 0,5 1 Hy H0 Figure 4 Characteristics of magnetoresistive sensors. The Barber pole structure enables a linear behaviour of the sensor for a small magnetic field. AN20 - 2 Figure 5 Wheatstone bridge of a magnetoresistive sensor with “Barber pole” structure. The bridge is balanced by laser trimming. The resistance of one resistor increases, whilst the other resistor has a lower resistance due to the differing field characteristic. Adding a second half bridge with an opposite arrangement of “Barber poles” provides a Wheatstone bridge. The voltage difference V0 is the output signal of the sensor. Each half bridge is trimmed to Vb/2 w ith an additional resistor in order to get an output voltage close to zero when no external field is applied. The trimming structures of the resistors in Figure 1 mark off the meander stripes on the left and right side of the chips. Operating conditions and parameters The shape of the stripe and the anisotropy of permalloy only define an ax is along the x-direction for the magnetisation without external field Hy. This means that in this state the stripe can have areas with a different direction of magnetisation (magnetic domains) and the sensor does not work in a stable way. A safe operation of the sensor is achieved by applying an auxiliary field Hx. This field defines the direction of the magnetisation. The range of Hy for safe sensor operation is determined by the strength of the auxiliary field. The safe operating area (SOA) of the sensor is demonstrated in Figure 6. The field Hxtot = Hy + Hd determines the allowed field values for Hy, where Hd is an external disturbing field in the x-direction. There is no limitation for Hy in the case of Hxtot ≥ 2.6 kA/m (ZMY20/ZMZ20). A small permanent magnet is sufficient to create the auxiliary field. The magnet can be glued on the sensor package (ZMZ 20/30 or ZMY 20/30). Another option is the ZMY20M which provides a very compact sensor including an integrated magnet, and is available in a surface mount package. AN20 - 3 Application Note 20 Issue 1 April 1996 Application Note 20 Issue 1 April 1996 determined by the geometrical di m e n s io ns of the s tri pe and the magnetic anisotropy of permalloy. This is taken into account by introducing a f i e l d H0 t h a t r e p r e s e n t s t h e demagnetising and anisotropic field. One obtains sin2 α = Hy2 H02 sin2 α = 1 Figure 3 Covering the stripe with “Barber poles” consisting of aluminium changes the direction of the current. This does not influence the direction of magnetisation. for H < H0 for H > H0 The characteristic of a magnetoresistive stripe as a field sensor is: Hy 2 R = R0 + ∆R0 1− 2 H0 for H < H0 A linear characteristic of the magnetoresistive sensor is required to measure a small magnetic field. The linear behaviour of the magnetoresistive sensor is achieved by using a “Barber pole” geometry. The stripes in Figure 1 are covered with aluminium bars having an inclination of 45° to the stripe axis. Aluminum has a low resistivity compared to permalloy. Therefore the Barber poles cause a change of the current direction. The angle between current and magnetisation is shifted by 45° as shown in Figure 3. The relationship between resistance and magnetic field is now Hy R =Ro + ∆R0 ± ∆Ro 2 Ho H √ 1− H y 0 The stripes of the magnetoresistive chip are arranged as a meandering pattern. They form a Wheatstone bridge which is shown schematically in Figure 5. The applied voltage is Vb. Each half bridge consists of two resistors with different “Barber pole” orientations. The voltage between the resistors of a half bridge changes upon application of a magnetic field. R R0+∆R0 with Barber poles without Barber poles R0 2 -1 2 A linear characteristic of the sensor is given around Hy2/H20 = 0. The sign in this equation is determined by the inclination of the “Barber poles” (±45°) Figure 6 Safe operating area of ZMY20/ZMZ20. Hxtot=Hx + Hd ; Tamb = 25°C Hd = disturbing field. to the stripe axis. The characteristic of a sensor with and without Barber poles is presented in Figure 4. -0,5 0 0,5 1 Hy H0 Figure 4 Characteristics of magnetoresistive sensors. The Barber pole structure enables a linear behaviour of the sensor for a small magnetic field. AN20 - 2 Figure 5 Wheatstone bridge of a magnetoresistive sensor with “Barber pole” structure. The bridge is balanced by laser trimming. The resistance of one resistor increases, whilst the other resistor has a lower resistance due to the differing field characteristic. Adding a second half bridge with an opposite arrangement of “Barber poles” provides a Wheatstone bridge. The voltage difference V0 is the output signal of the sensor. Each half bridge is trimmed to Vb/2 w ith an additional resistor in order to get an output voltage close to zero when no external field is applied. The trimming structures of the resistors in Figure 1 mark off the meander stripes on the left and right side of the chips. Operating conditions and parameters The shape of the stripe and the anisotropy of permalloy only define an ax is along the x-direction for the magnetisation without external field Hy. This means that in this state the stripe can have areas with a different direction of magnetisation (magnetic domains) and the sensor does not work in a stable way. A safe operation of the sensor is achieved by applying an auxiliary field Hx. This field defines the direction of the magnetisation. The range of Hy for safe sensor operation is determined by the strength of the auxiliary field. The safe operating area (SOA) of the sensor is demonstrated in Figure 6. The field Hxtot = Hy + Hd determines the allowed field values for Hy, where Hd is an external disturbing field in the x-direction. There is no limitation for Hy in the case of Hxtot ≥ 2.6 kA/m (ZMY20/ZMZ20). A small permanent magnet is sufficient to create the auxiliary field. The magnet can be glued on the sensor package (ZMZ 20/30 or ZMY 20/30). Another option is the ZMY20M which provides a very compact sensor including an integrated magnet, and is available in a surface mount package. AN20 - 3 Application Note 20 Issue 1 April 1996 The operating datasheet parameters of the Wheatstone bridge are referred to an input voltage Vb= 1V, due to the linear relationship between input and output voltage in this region. The sensitivity S [mV/V/kA/m] of the magnetoresistive sensor is defined as the slope of the output voltage versus external field for -1 kA/m ≤ Hy ≤1 kA/m. This parameter depends on the geometry of the permalloy meander and t h e a u x i l i a r y f i e l d . T h e l a t te r i s demonstrated in Figure 7 for Hx = 3 kA/m a n d Hx = 6 k A / m . N o te t h e s m a l l operating area in the case of Hy = 0 kA/m. A high sensitivity of the sensor leads to a small operating area for H y. Further details and complete Magnetoresistive Product information is provided in the Appropriate Technical Handbook: please see Technical Publication section. Application Note 20 Issue 1 April 1996 The Wheatstone bridge is balanced without the application of an external field (Hy≤ 0.1 kA/m). In this case the output voltage of the sensor is close to zero at room temperature. The deviation of the output voltage from zero is called the offset voltage V0ff/Vb [mV/V]. The offset is caused by small geometric variations of the bridge which occur during the photolithographic process. The offset of the bridge is adjusted by laser trimming. The voltage output of each half bridge is Vb/2. The bridge resistance Rbr [%/K] of the ma gnetor esi sti v e s e n so r d e p e n d s linearly on temperature. The te m p e ra t ure coeff icient of bri dg e resistance TCRbr [%/K] is positive. This is typical for metals. The temperature coefficient of sensitivity TCS [%/K] of the sensor is negative for VB = const (TCSV), because the strength of the m a g n e t o r e s i s t i v e e f f e c t be c om e s smaller with increasing temperature. In the case of IB = const (TCSI), when the sensor is powered by a constant current supply, the temperature dependence of the sensitivity is reduced due to the linear relationship between input and o u t p u t v o l t a ge . A hi g h e r br i d g e resistance caused by a rise in temperature leads to an increased applied voltage, partly compensating the change of sensitivity. Figure 7 Sensor output characteristic of ZMY20/ZMZ20. The sensitivity of the sensor can be controlled by applying an auxiliary field Hx. This auxiliary field is necessary for sensor operation in a large field range. V0=f(Hy); HX-parameter;VB=const;Tamb=25°C. AN20 - 4 The Wheatstone bridge cannot fully compensate the temperature de pe nd en c e of the r es i stor s. The t e m p e r a t u r e c oe ff i c i e n t o f o f f s e t voltage TCVoff [µV/V/K] is due to local changes of resistivity in the permalloy thin film and photolithographic variations. This characteristic of the magnetoresistive sensor limits the measurement of small magnetic fields in a wide temperature range, especially in the case of static fields. Two sensors can b e s e l e c t ed h a v in g a c omp ar a b l e temperature coefficient. The offset drift i s p a r t l y e l i m in a t e d b y u si n g t h e difference of the output voltages of both sensors. Another elegant way to avoid offset drift is to invert the direction of the auxiliary field and thus inverting the output voltage of the sensor. This can be d o n e b y s m al l c oil s p r ov idi ng an auxiliary field that can change its direction. The hysteresis of output voltage V0ffH/Vb [µV/V] describes the accuracy of the magnetoresistive sensor. The magnetisation of the permalloy stripe is not completely homogenous. There are small areas of the meander, especially at the corners of the stripes, where the magnetisation is pinned and does not correctly follow the external field. The hysteresis is measured in a magnetic field loop, where H y goes from -3 kA/m to 3 kA/m and back to 0 kA/m (Hx = 3 kA/m). V0ffH/Vb denotes the shift of the offset voltage caused by this loop. The maximum range of output voltage ∆V0/Vb [ m V / V ] i s d e f i n e d a s th e difference of output voltage for α = 0° and α = 90°, where α denotes the angle between current and magnetisation of the magnetoresistive stripe. This means that ∆V0/Vb represents the strength of the magnetoresistive effect. This parameter decreases with temperature and determines the sensitivity of the sensor. (An example of a typical Magnetoresistive sensor datasheet, is partially reproduced in Appendix B.) AN20 - 5 Application Note 20 Issue 1 April 1996 The operating datasheet parameters of the Wheatstone bridge are referred to an input voltage Vb= 1V, due to the linear relationship between input and output voltage in this region. The sensitivity S [mV/V/kA/m] of the magnetoresistive sensor is defined as the slope of the output voltage versus external field for -1 kA/m ≤ Hy ≤1 kA/m. This parameter depends on the geometry of the permalloy meander and t h e a u x i l i a r y f i e l d . T h e l a t te r i s demonstrated in Figure 7 for Hx = 3 kA/m a n d Hx = 6 k A / m . N o te t h e s m a l l operating area in the case of Hy = 0 kA/m. A high sensitivity of the sensor leads to a small operating area for H y. Further details and complete Magnetoresistive Product information is provided in the Appropriate Technical Handbook: please see Technical Publication section. Application Note 20 Issue 1 April 1996 The Wheatstone bridge is balanced without the application of an external field (Hy≤ 0.1 kA/m). In this case the output voltage of the sensor is close to zero at room temperature. The deviation of the output voltage from zero is called the offset voltage V0ff/Vb [mV/V]. The offset is caused by small geometric variations of the bridge which occur during the photolithographic process. The offset of the bridge is adjusted by laser trimming. The voltage output of each half bridge is Vb/2. The bridge resistance Rbr [%/K] of the ma gnetor esi sti v e s e n so r d e p e n d s linearly on temperature. The te m p e ra t ure coeff icient of bri dg e resistance TCRbr [%/K] is positive. This is typical for metals. The temperature coefficient of sensitivity TCS [%/K] of the sensor is negative for VB = const (TCSV), because the strength of the m a g n e t o r e s i s t i v e e f f e c t be c om e s smaller with increasing temperature. In the case of IB = const (TCSI), when the sensor is powered by a constant current supply, the temperature dependence of the sensitivity is reduced due to the linear relationship between input and o u t p u t v o l t a ge . A hi g h e r br i d g e resistance caused by a rise in temperature leads to an increased applied voltage, partly compensating the change of sensitivity. Figure 7 Sensor output characteristic of ZMY20/ZMZ20. The sensitivity of the sensor can be controlled by applying an auxiliary field Hx. This auxiliary field is necessary for sensor operation in a large field range. V0=f(Hy); HX-parameter;VB=const;Tamb=25°C. AN20 - 4 The Wheatstone bridge cannot fully compensate the temperature de pe nd en c e of the r es i stor s. The t e m p e r a t u r e c oe ff i c i e n t o f o f f s e t voltage TCVoff [µV/V/K] is due to local changes of resistivity in the permalloy thin film and photolithographic variations. This characteristic of the magnetoresistive sensor limits the measurement of small magnetic fields in a wide temperature range, especially in the case of static fields. Two sensors can b e s e l e c t ed h a v in g a c omp ar a b l e temperature coefficient. The offset drift i s p a r t l y e l i m in a t e d b y u si n g t h e difference of the output voltages of both sensors. Another elegant way to avoid offset drift is to invert the direction of the auxiliary field and thus inverting the output voltage of the sensor. This can be d o n e b y s m al l c oil s p r ov idi ng an auxiliary field that can change its direction. The hysteresis of output voltage V0ffH/Vb [µV/V] describes the accuracy of the magnetoresistive sensor. The magnetisation of the permalloy stripe is not completely homogenous. There are small areas of the meander, especially at the corners of the stripes, where the magnetisation is pinned and does not correctly follow the external field. The hysteresis is measured in a magnetic field loop, where H y goes from -3 kA/m to 3 kA/m and back to 0 kA/m (Hx = 3 kA/m). V0ffH/Vb denotes the shift of the offset voltage caused by this loop. The maximum range of output voltage ∆V0/Vb [ m V / V ] i s d e f i n e d a s th e difference of output voltage for α = 0° and α = 90°, where α denotes the angle between current and magnetisation of the magnetoresistive stripe. This means that ∆V0/Vb represents the strength of the magnetoresistive effect. This parameter decreases with temperature and determines the sensitivity of the sensor. (An example of a typical Magnetoresistive sensor datasheet, is partially reproduced in Appendix B.) AN20 - 5 Application Note 20 Issue 1 April 1996 Application Note 20 Issue 1 April 1996 6 +5V R1 10k R3 10k P1 10k 4 * U1D 13 14 R3 R17 R19 10k 200k 1M ZMZ20 6 R4 24k B1 ZMC20 * R14 100k VDD U1B 7 4 * 3 U2D 13 14 R4 R18 R20 10k 200k 1M 1k * R7 R2 10k 1 R21 1M 4 TL064 U3B 3 VSS R12 1 2 10k Output Figure 9 Sensor for Revolution Measurement. from disturbing fields (generated by supp ly lines, c ar alt ernato rs e tc.) Supporting software for these systems is available on request. Adjust Offset 4 Ground Figure 8 Overcurrent Switch using the ZMC20, for Protection of Power IGBTs. AN20 - 7 330R TL064 11 R22 T1 R8 20k AN20 - 6 * 11 * R11 10k 1 T1 BC369 680k 10k U3A MC33172 3 VSS C2 470n TL064 MC33172 4 R8 * U2C 10 VDD R15 100k TL064 TL064 8 +5V R16 100k 6 10k 9 2 7 2 TL064 4 5 R6 12 3 U2B 5 U2A 1 R9 6 2 R10 10k * R2 10k TL064 5 5 U1A 3 1 R5 24k VSS C1 470n 8 10 * 8 1 * * R7 U1C 9 10k TL064 11 * B1 R6 680k 8 6 10k TL064 TL064 Output I mess + 8,9,10 R5 1 7 2 12 Adjust Offset 11,12,13 - R9 10k U1B 5 U1A 3 * Figure 10 shows an application circuit for t h r e e - d i m e ns i on a l m a g ne ti c fi e l d observation. When the unit is enabled, it calibrates itself to the existing magnetic field of the earth, and then generates a warning signal if it is moved. The system employs three ZMY20 sensors (one for each dimension) and a CMOS EPROM microcontroller with an A/D converter. Similar circuits have been designed for automotive immobiliser/alarm systems that monitor the position of the vehicle by sensing the magnetic field of a movab le permanent magnet. This magnet is necessary to shield the sensor VDD 4 Figure 8 shows a ZMC20 current sensor being used as a basis for an overcurrent trip switch used to protect power IGBTs within a motor driver system. The circuit reacts within 3µs to prevent latch-up related failure under transient/pulse conditions, and was built within a module measuring 35 x 20 x 25mm. An external 10kΩ preset is required for offset adjustment. Supply voltage is +5V ± 10% at 10mA; output is via an open collector transistor rated ar 1A, 20V; operating temperature range is 0 to 80°C. R13 100k 11 [Please refer to appendix A which summarises some graphic examples of applic ations for m a gnetore s is tiv e sensors]. R1 10k * Figure 9 provides a method for revolution measurement by reacting to a modulated magnetic field due to a rotating cog. The circuit gives a signal whose frequency is proportional to the rotational velocity of the cog, and a high level output for no rotation. Applications Application Note 20 Issue 1 April 1996 Application Note 20 Issue 1 April 1996 6 +5V R1 10k R3 10k P1 10k 4 * U1D 13 14 R3 R17 R19 10k 200k 1M ZMZ20 6 R4 24k B1 ZMC20 * R14 100k VDD U1B 7 4 * 3 U2D 13 14 R4 R18 R20 10k 200k 1M 1k * R7 R2 10k 1 R21 1M 4 TL064 U3B 3 VSS R12 1 2 10k Output Figure 9 Sensor for Revolution Measurement. from disturbing fields (generated by supp ly lines, c ar alt ernato rs e tc.) Supporting software for these systems is available on request. Adjust Offset 4 Ground Figure 8 Overcurrent Switch using the ZMC20, for Protection of Power IGBTs. AN20 - 7 330R TL064 11 R22 T1 R8 20k AN20 - 6 * 11 * R11 10k 1 T1 BC369 680k 10k U3A MC33172 3 VSS C2 470n TL064 MC33172 4 R8 * U2C 10 VDD R15 100k TL064 TL064 8 +5V R16 100k 6 10k 9 2 7 2 TL064 4 5 R6 12 3 U2B 5 U2A 1 R9 6 2 R10 10k * R2 10k TL064 5 5 U1A 3 1 R5 24k VSS C1 470n 8 10 * 8 1 * * R7 U1C 9 10k TL064 11 * B1 R6 680k 8 6 10k TL064 TL064 Output I mess + 8,9,10 R5 1 7 2 12 Adjust Offset 11,12,13 - R9 10k U1B 5 U1A 3 * Figure 10 shows an application circuit for t h r e e - d i m e ns i on a l m a g ne ti c fi e l d observation. When the unit is enabled, it calibrates itself to the existing magnetic field of the earth, and then generates a warning signal if it is moved. The system employs three ZMY20 sensors (one for each dimension) and a CMOS EPROM microcontroller with an A/D converter. Similar circuits have been designed for automotive immobiliser/alarm systems that monitor the position of the vehicle by sensing the magnetic field of a movab le permanent magnet. This magnet is necessary to shield the sensor VDD 4 Figure 8 shows a ZMC20 current sensor being used as a basis for an overcurrent trip switch used to protect power IGBTs within a motor driver system. The circuit reacts within 3µs to prevent latch-up related failure under transient/pulse conditions, and was built within a module measuring 35 x 20 x 25mm. An external 10kΩ preset is required for offset adjustment. Supply voltage is +5V ± 10% at 10mA; output is via an open collector transistor rated ar 1A, 20V; operating temperature range is 0 to 80°C. R13 100k 11 [Please refer to appendix A which summarises some graphic examples of applic ations for m a gnetore s is tiv e sensors]. R1 10k * Figure 9 provides a method for revolution measurement by reacting to a modulated magnetic field due to a rotating cog. The circuit gives a signal whose frequency is proportional to the rotational velocity of the cog, and a high level output for no rotation. Applications R10 100k R9 100k 3 3 B1 ZMY20 1 2 ZMY20 B2 1 2 3 B3 ZMY20 X X X X 2 3 X U1B 4066 VDD 11 4 11 1 4 4 11 4 Y U1C Y 4066 U2A Y 4066 U2B Y 4066 2 3 MC33174 1 10 10 2 10 U3A U2B Y 4066 12 1 2 C 13 C 12 C 5 C 13 C C 12 4 11 8 4 X U2D 4066 9 3 T1 ZVP2106 Y X U2C Y 4066 C 5 C 6 3 VCC VO 33k 33k R14 R13 33k R12 VI U5 ZSR600 12 13 R11 33k 9 10 1 8 14 D1 DIODE MC33174 U3D 100k R8 100k R7 MC33174 U3C S1 D3 ZRA500 R1 10k R3 10k R2 10k 7 Ground 22p C2 QUARTZ Q1 22p C3 MC33174 U3B 100k R5 +12V R6 100k 5 6 * * * * * * R4 14 15 16 4 3 2 OSC2/CLK OSC1 MCLR/VPP RA4/RTCC RA3/AIN3 RA2/AIN2 RA1/AIN1 11 12 13 RB6 RB7 10 9 8 RB5 RB4 RB3 RB2 RB1 7 1 6 RA0/AIN0 RB0/INT 1u5 C1 18 VCC 17 U4 PIC16C71 100k VDD VSS X U1A Y 4066 GND 2 AN20 - 8 5 1 LS1 D2 LED R15 430R Application Note 20 Issue 1 April 1996 Application Note 20 Issue 1 April 1996 Figure 10 Sensor System used to Monitor Movement in the Earth’s Magnetic Field. AN20 - 9 Application Note 20 Issue 1 April 1996 Application Note 20 Issue 1 April 1996 Appendix A Magnetoresistive sensor Basic Function/Application Examples. Measurement of Current (AC or DC) Detection of Ferromagnetic Objects Measurement of Angular Position Measurement of Rotation Speed Position Sensor AN20 - 16 Measurement of the Earth’s Magnetic Field AN20 - 9 Application Note 20 Issue 1 April 1996 Application Note 20 Issue 1 April 1996 Appendix B Partial Characterisation for ZMY20/30, ZMZ20/30 Magnetoresistive Sensors. ELECTRICAL CHARACTERISTICS (at Tamb = 25 °C and Hx = 3 kA/m unless otherwise stated) AN20 - 12 Parameter Symbol Min. Typ. Max. Unit Bridge resistance ZMY20/ZMZ20 ZMY30/ZMZ30 R br Output voltage range ZMY20/ZMZ20 ZMY30/ZMZ30 VO/VB Open circuit sensitivity ZMY20/ZMZ20 ZMY30/ZMZ30 1.2 2.0 1.7 3.0 2.2 4.0 kΩ 16 12 18 16 22 20 mV/V S 3.2 2.0 4.0 3.0 4.8 4.0 (mV/V)/ (kA/m) no disturbing field Hd allowed Hysteresis of output voltage VOH /VB - - 50 µV/V Hy ≤ 2 kA/m Offset voltage Voff /VB -1.0 - +1.0 mV/V Operating frequency fmax 0 - 1 MHz Temperature coefficient of offset voltage TCVoff -3 - +3 (µV/V)/K Tamb = -25...+125°C Temperature coefficient of bridge resistance TCRbr - 0.3 - %/K Tamb = -25...+125°C Temperature coefficient of open circuit sensitivity VB = 5 V TCS V - -0.4 - %/K Tamb = -25...+125°C Temperature coefficient of open circuit sensitivity I B = 3 mA TCS I - -0.1 - %/K Tamb = -25...+125°C AN20 -10 Test conditions