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19-4283; Rev 0; 10/08
Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold
General Description
The MAX9924-MAX9927 variable reluctance (VR or magnetic coil) sensor interface devices are ideal for position and speed sensing for automotive crankshafts, camshafts, transmission shafts, etc. These devices integrate a precision amplifier and comparator with selectable adaptive peak threshold and zero-crossing circuit blocks that generate robust output pulses even in the presence of substantial system noise or extremely weak VR signals. The MAX9926/MAX9927 are dual versions of the MAX9924/MAX9925, respectively. The MAX9924/ MAX9926 combine matched resistors with a CMOS input precision operational amplifier to give high CMRR over a wide range of input frequencies and temperatures. The MAX9924/MAX9926 differential amplifiers provide a fixed gain of 1V/V. The MAX9925/MAX9927 make all three terminals of the internal operational amplifier available, allowing greater flexibility for gain. The MAX9926 also provides a direction output that is useful for quadratureconnected VR sensors that are used in certain high-performance engines. These devices interface with both new-generation differential VR sensors as well as legacy single-ended VR sensors. The MAX9924/MAX9925 are available in the 10-pin MAX (R) package, while the MAX9926/MAX9927 are available in the 16-pin QSOP package. All devices are specified over the -40C to +125C automotive temperature range.
Features
Differential Input Stage Provides Enhanced Noise Immunity Precision Amplifier and Comparator Allows Small-Signal Detection User-Enabled Internal Adaptive Peak Threshold or Flexible External Threshold Zero-Crossing Detection Provides Accurate Phase Information
MAX9924-MAX9927
Ordering Information
PART MAX9924UAUB+ MAX9925AUB+ MAX9926UAEE+* MAX9927AEE+* TEMP RANGE -40C to +125C -40C to +125C -40C to +125C -40C to +125C PIN-PACKAGE 10 MAX 10 MAX 16 QSOP 16 QSOP
+Denotes a lead-free/RoHS-compliant package. *Future product--contact factory for availability.
Selector Guide
PART MAX9924UAUB MAX9925AUB MAX9926UAEE MAX9927AEE AMPLIFIER 1 x Differential 1 x Operational 2 x Differential 2 x Operational GAIN 1V/V Externally Set 1V/V Externally Set
Applications
Camshaft VRS Interfaces Crankshaft VRS Interfaces Vehicle Speed VRS Interfaces
MAX is a registered trademark of Maxim Integrated Products, Inc.
Simplified Block Diagram
ENGINE BLOCK
MAX9924
VR SENSOR DIFFERENTIAL AMPLIFIER ADAPTIVE/MINIMUM AND ZERO-CROSSING THRESHOLDS INTERNAL/EXTERNAL BIAS VOLTAGE C
________________________________________________________________ Maxim Integrated Products
1
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
ABSOLUTE MAXIMUM RATINGS
VCC to GND .............................................................-0.3V to + 6V All Other Pins..............................................-0.3V to (VCC + 0.3V) Current into IN+, IN-, IN_+, IN_-.......................................40mA Current into All Other Pins ................................................20mA Output Short-Circuit (OUT_, OUT) to GND.............................10s Continuous Power Dissipation (TA = +70C) (Note 1) 10-Pin MAX (derate 8.8mW/C above +70C) ........707.3mW 16-Pin QSOP (derate 9.6mW/C above +70C)........771.5mW Junction-to-Case Thermal Resistance (JC) (Note 1) 10-Pin MAX.................................................................42C/W 16-Pin QSOP ................................................................37C/W Junction-to-Ambient Thermal Resistance (JA) (Note 1) 10-Pin MAX............................................................113.1C/W 16-Pin QSOP ...........................................................103.7C/W Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = 5V, VGND = 0, MAX9925/MAX9927 gain setting = 1V/V, Mode A1, VBIAS = 2.5V, VPULLUP = 5V, RPULLUP = 1k, CCOUT = 50pF. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 2)
PARAMETER POWER SUPPLY Operating Supply Range Supply Current Power-On Time VCC ICC PON (Note 3) MAX9924/MAX9925 MAX9926/MAX9927 VCC > VUVLO = 4.1V, step time for VCC ~ 1s Guaranteed by CMRR Temperature drift 0.5 (Note 4) (Note 4) From VCM = 0 to VCC Over operating VCC range IOL = 1mA IOH = -1mA To 1% of the actual VOUT after output saturates VCC 0.050 1.2 1.4 2.3 RIN = 100k, f = 1Hz to 10kHz 12 1.3 76 88 0.001 0.001 102 105 0.050 0 4.5 2.6 4.7 30 5.5 5 10 150 V mA s SYMBOL CONDITIONS MIN TYP MAX UNITS
INPUT OPERATIONAL AMPLIFIER (MAX9925/MAX9927) Input Voltage Range Input Offset Voltage Input Bias Current Input Offset Current Common-Mode Rejection Ratio Power-Supply Rejection Ratio Output Voltage Low Output Voltage High Recovery Time from Saturation Gain-Bandwidth Product Slew Rate Input Noise Charge-Pump Frequency IN+, INVOS-OA IBIAS IOFFSET CMRR PSRR VOL VOH tSAT GBW SR en fCP VCC 5 3 6 2 V V/C mV nA nA dB dB V V s MHz V/s VRMS MHz
2
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 5V, VGND = 0, MAX9925/MAX9927 gain setting = 1V/V, Mode A1, VBIAS = 2.5V, VPULLUP = 5V, RPULLUP = 1k, CCOUT = 50pF. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX VCC + 0.3 87 100 33 4 15 30 135 UNITS INPUT DIFFERENTIAL AMPLIFIER (MAX9924/MAX9926) Input Voltage Range Differential Common-Mode Rejection Ratio Input Resistance ADAPTIVE PEAK DETECTION VADAPTIVE Adaptive peak threshold Minimum threshold of hysteresis comparator MAX9924/MAX9926 (Notes 5, 6) Fixed and Adaptive Peak Threshold Minimum threshold of hysteresis comparator MAX9925/MAX9927 (Notes 5, 6) VMIN-THRESH - VZERO-THRESH for MAX9924/MAX9926 (Notes 3, 4) VMIN-THRESH - VZERO-THRESH for MAX9925/MAX9927 (Notes 3, 4) Watchdog Timeout for Adaptive Peak Threshold ENTIRE SYSTEM Zero-Crossing Threshold Comparator Output Low Voltage Propagation Delay COUT Transition Time Propagation Delay Jitter EXT Mode B, TA = +125C EXT Voltage Range VEXT Mode C, TA = +125C Input Current to EXT IEXT 0.12 1.5 VCC - 1.1 V VCC - 1.1 10 A VZERO_THRESH VCOUT_OL tPDZ tPDA tHL-LH tPD-JITTER Includes noise of differential amplifier and comparator, f = 10kHz, VIN = 1VP-P sine wave Overdrive = 2V to 3V, zero-crossing Overdrive = 2V to 3V, adaptive peak 50 150 2 20 Mode B operation (Notes 5, 6) -6.5 0 +6.5 0.2 mV V ns ns ns tWD Timing window to reset the adaptive peak threshold if not triggered (input level below threshold) %PK IN+, INCMRR RIN Guaranteed by CMRR (Note 5) (Note 5) -0.3 60 65 V dB k
MAX9924-MAX9927
VMIN-THRESH
21
30
43
mV
7 22
26 42
45
85
140
ms
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 5V, VGND = 0, MAX9925/MAX9927 gain setting = 1V/V, Mode A1, VBIAS = 2.5V, VPULLUP = 5V, RPULLUP = 1k, CCOUT = 50pF. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 2)
PARAMETER DIRN (MAX9926 Only) Output Low Voltage INT_THRS, ZERO_EN Low Input High Input Input Leakage Input Current ZERO_EN Switching Time Between Modes A1, A2, and Modes B, C BIAS Input Current to BIAS BIAS Voltage Range Internal BIAS Reference Voltage IBIAS VBIAS VINT_BIAS Modes A1, B Modes A1, B, TA = +125C Mode A2 (MAX9924/MAX9926) 0.2 2.46 1 VCC - 1.1 A V V VIL VIH ILEAK ISINK Pullup resistor = 10k, VZERO_EN = GND With INT_THRS = GND, auto peakdetect is disabled, and EXT_THRS is active 500 0.7 x VCC 1 800 0.3 x VCC V V A A 0.2 V SYMBOL CONDITIONS MIN TYP MAX UNITS
tSW
3
s
Note 2: Note 3: Note 4: Note 5: Note 6:
Specifications are 100% tested at TA = +125C, unless otherwise noted. All temperature limits are guaranteed by design. Inferred from functional PSRR. CMOS inputs. Guaranteed by design. Includes effect of VOS of internal op amp and comparator.
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold
Typical Operating Characteristics
(VCC = 5V, VGND = 0, MAX9925/MAX9927 gain setting = 1V/V. All values are at TA = +25C, unless otherwise noted.)
INPUT OFFSET VOLTAGE vs. INPUT COMMON-MODE VOLTAGE
MAX9924 toc01 MAX9924 toc02
MAX9924-MAX9927
INPUT OFFSET VOLTAGE DISTRIBUTION
20 VCM = 0 BIN SIZE = 250 PERCENTAGE OF UNITS (%) 15 0.5
COMMON-MODE REJECTION RATIO vs. FREQUENCY
MAX9924 toc03
120 100 80 CMRR (dB)
INPUT OFFSET VOLTAGE (mV)
0.4
0.3
10
60 40
0.2
5
0.1 VOUT = 2.5V MAX9925
20 0 1
0 0 2000 3000 -2000 -1000 1000 -500 500 1500 2500 -1500 INPUT OFFSET VOLTAGE (V)
0 -0.5 0.5 1.5 2.5 3.5 4.5 5.5 INPUT COMMON-MODE VOLTAGE (V)
VBIAS = VOUT = 2.5V VCM = 2VP-P CMRR = 20log(ADM/ACM) 10 100 1k 10k 100k
FREQUENCY (Hz)
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX9924 toc04
OPEN LOOP FREQUENCY RESPONSE
VCC = 5V VBIAS = 2.5V VOUT = 2VP-P MAX9925
MAX9924 toc05
VOL AND VOH vs. TEMPERATURE
35 30 VOL AND VOH (mV) 25 VCC - VOH 20 15 10 VOL
MAX9924 toc06
0 -10 -20 -30 PSSR (dB) -40 -50 -60 -70 -80 -90 -100 -110 -120 1
VRIPPLE = 100mVP-P VBIAS = VOUT = 2.5V INPUTS COUPLED TO GND
125
40
100
GAIN (dB)
75
50
25 5 10 100 1k 10k 100k 0 0.001 0 0.1 FREQUENCY (kHz) 10 -50 -25 0 25 50 75 100 125 TEMPERATURE (C)
FREQUENCY (Hz)
INPUT OFFSET VOLTAGE vs. TEMPERATURE
MAX9924 toc07
ADAPTIVE THRESHOLD AND RATIO vs. SIGNAL LEVEL
MAX9924 toc08
ADAPTIVE THRESHOLD vs. TEMPERATURE
350 300 THRESHOLD (mV) 250 200 150 100 VIN = 2VP-P fIN = 1kHz MAX9924 -50 -25 0 25 50 75 100 125
MAX9924 toc09
0.6 0.5 0.4 0.3 VCM = 2.5V 0.2 0.1 0 -50 -25 0 25 50
ADAPTIVE THRESHOLD LEVEL (mV)
VOUT = 2.5V MAX9925
900 800 700 600 500 400 300 200 100 0 fIN = 1kHz MAX9924 0 0.5 1.0 1.5 2.0
400
INPUT OFFSET VOLTAGE (mV)
VCM = 0
50 0 2.5 TEMPERATURE (C)
75
100
125
TEMPERATURE (C)
SIGNAL LEVEL (VP)
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Typical Operating Characteristics (continued)
(VCC = 5V, VGND = 0, MAX9925/MAX9927 gain setting = 1V/V. All values are at TA = +25C, unless otherwise noted.)
MINIMUM AND ZERO-CROSSING THRESHOLD vs. TEMPERATURE
MAX9924 toc10
CMRR vs. TEMPERATURE
MAX9924 toc11
INPUT SIGNAL vs. COUT WITH WATCHDOG TIMER EXPIRED
MAX9924 toc12
30 25 THRESHOLD (mV) 20 15 10 5 0 -5 -50 -25 0 25 50 75 100 ZERO CROSSING AT 1Hz ZERO CROSSING AT 5Hz VCM = 2.5V fIN = 5Hz MINIMUM THRESHOLD
100
COUT 5V
INPUT SIGNAL
75 CMRR (dB)
50
VBIAS
25 MAX9924 VCM = 0 TO 5V 0 125 -50 -25 0 25 50 75 100 125 20ms/div fIN = 5Hz
TEMPERATURE (C)
TEMPERATURE (C)
INPUT SIGNAL vs. COUT WITH WATCHDOG TIMER EXPIRED
MAX9924 toc13
OVERDRIVEN INPUT VOLTAGES (MAX9924)
MAX9924 toc14
DIRN OPERATION (MAX9924)
MAX9924 toc15
COUT 5V
INPUT SIGNAL
833mV VBIAS
fIN = 1kHz 100s/div 100s/div 200s/div
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Pin Description
PIN MAX9924 1 2 -- 3 4 5 6 7 8 9 10 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- MAX9925 1 2 3 -- 4 5 6 7 8 9 10 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- MAX9926 -- -- -- -- -- 11 13 -- -- -- 14 1 2 3 4 5 6 7 8 9 10 12 -- -- 15 16 MAX9927 -- -- -- -- -- 11 -- -- -- -- 14 1 2 3 4 5 6 7 8 9 10 -- 12 13 15 16 NAME IN+ INOUT N.C. BIAS GND ZERO_EN COUT EXT INT_THRS VCC INT_THRS1 EXT1 BIAS1 COUT1 COUT2 BIAS2 EXT2 INT_THRS2 IN2+ IN2DIRN OUT2 OUT1 IN1IN1+ Noninverting Input Inverting Input Amplifier Output No Connection. Not internally connected. Input Bias. Connect to an external resistor-divider and bypass to ground with a 0.1F and 10F capacitor. Ground Zero-Crossing Enable. Mode configuration pin, internally pulled up to VCC with 10k resistor. Comparator Output. Open-drain output, connect a 10k pullup resistor from COUT to VPULLUP. External Reference Input. Leave EXT unconnected in Modes A1, A2. Apply an external voltage in Modes B, C. Internal Adaptive Threshold. Mode configuration pin. Power Supply Internal Adaptive Threshold 1. Mode configuration pin. External Reference Input 1. Leave EXT unconnected in Modes A1, A2. Apply an external voltage in Modes B, C. Input Bias 1. Connect to an external resistor-divider and bypass to ground with a 0.1F and 10F capacitor. Comparator Output 1. Open-drain output, connect a 10k pullup resistor from COUT1 to VPULLUP. Comparator Output 2. Open-drain output, connect a 10k pullup resistor from COUT2 to VPULLUP. Input Bias 2. Connect to an external resistor-divider and bypass to ground with a 0.1F and 10F capacitor. External Reference Input 2. Leave EXT unconnected in Modes A1, A2. Apply an external voltage in Modes B, C. Internal Adaptive Threshold 2. Mode configuration pin. Noninverting Input 2 Inverting Input 2 Rotational Direction Output. Open-drain output, connect a pullup resistor from DIRN to VPULLUP. Amplifier Output 2 Amplifier Output 1 Noninverting Input 1 Inverting Input 1 FUNCTION
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Functional Diagrams
VCC 100k INVCC
100k VCC
MAX9924
OP AMP 100k GND
IN+ 100k COMPARATOR 65ms WATCHDOG COUT
INTERNAL REFERENCE 2.5V BUFFER
30% BIAS PEAK DETECTOR VMIN THRESHOLD MODE LOGIC MODE LOGIC
VCC
10k ZERO_EN INT_THRS
INT_THRS
EXT
8
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Functional Diagrams (continued)
OUT
VCC
VCC
IN-
VCC OP AMP
MAX9925
GND
IN+ COMPARATOR 85ms WATCHDOG COUT
BIAS
BUFFER
30% PEAK DETECTOR VMIN THRESHOLD MODE LOGIC
VCC
10k ZERO_EN INT_THRS
EXT
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Functional Diagrams (continued)
VCC 100k IN1VCC OP AMP 100k IN1+ 100k COMPARATOR 85ms WATCHDOG COUT1 100k VCC
MAX9926
GND
INTERNAL REFERENCE 2.5V BUFFER
30% BIAS1 PEAK DETECTOR VMIN THRESHOLD CLK
DIRN FLIP-FLOP
DIRN
EXT1 VCC 100k IN2VCC OP AMP 100k IN2+ 100k COMPARATOR 85ms WATCHDOG COUT2 100k
BUFFER
30% BIAS2 PEAK DETECTOR VMIN THRESHOLD
VCC
10k MODE LOGIC ZERO_EN INT_THRS1 INT_THRS2
EXT2
10
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold
Functional Diagrams (continued)
OUT1
MAX9924-MAX9927
VCC
VCC
IN1-
VCC OP AMP
MAX9927
GND
IN1+ COMPARATOR 85ms WATCHDOG COUT1
BIAS1
BUFFER
30% PEAK DETECTOR VMIN THRESHOLD VCC EXT1
IN2-
VCC OP AMP OUT1
IN2+ COMPARATOR 85ms WATCHDOG COUT2
BIAS2
BUFFER
30% PEAK DETECTOR VMIN THRESHOLD MODE LOGIC INT_THRS1 INT_THRS2
EXT2
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Detailed Description
The MAX9924-MAX9927 interface with variable reluctance (VR) or magnetic coil sensors. These devices produce accurate pulses aligned with flywheel gearteeth even when the pickup signal is small and in the presence of large amounts of system noise. They interface with new-generation differential VR sensors as well as legacy single-ended VR sensors. The MAX9924/MAX9925 integrate a precision op amp, a precision comparator, an adaptive peak threshold block, a zero-crossing detection circuit, and precision matched resistors (MAX9924). The MAX9926 and MAX9927 are dual versions of the MAX9924 and MAX9925, respectively. The MAX9926 also provides a rotational output that is useful for quadrature-connected VR sensors used in certain high-performance engines. The input op amp in the MAX9925/MAX9927 are typically configured as a differential amplifier by using four external resistors (the MAX9924/MAX9926 integrate precision-matched resistors to give superior CMRR performance). This input differential amplifier rejects input common-mode noise and converts the input differential signal from a VR sensor into a single-ended signal. The internal comparator produces output pulses by comparing the output of the input differential amplifier with a threshold voltage that is set depending on the mode that the device is in (see the Mode Selection section).
Mode Selection
The MAX9924/MAX9926 provide four modes of operation: Mode A1, Mode A2, Mode B, and Mode C as determined by voltages applied to inputs ZERO_EN and INT_THRS (see Tables 1, 2, and 3). In Modes A1 and A2, the internal adaptive peak threshold and the zerocrossing features are enabled. In Mode A2, an internally generated reference voltage is used to bias the differential amplifier and all internal circuitry instead of an external voltage connected to the BIAS input--this helps reduce external components and design variables leading to a more robust application. In Mode B, the adaptive peak threshold functionality is disabled, but zero-crossing functionality is enabled. In this mode, an external threshold voltage is applied at EXT allowing application-specific adaptive algorithms to be implemented in firmware. In Mode C, both the adaptive peak threshold and zero-crossing features are disabled and the device acts as a high-performance differential amplifier connected to a precision comparator (add external hysteresis to the comparator for glitch-free operation).
Table 1. MAX9924/MAX9926 Operating Modes
SETTING OPERATING MODE A1 A2 B C ZERO_EN VCC GND VCC GND INT_THRS VCC GND GND VCC ZERO CROSSING Enabled Enabled Enabled Disabled DEVICE FUNCTIONALITY ADAPTIVE PEAK THRESHOLD Enabled Enabled Disabled Disabled BIAS VOLTAGE SOURCE External Internal Ref External External
Table 2. MAX9925 Operating Modes
OPERATING MODE A1 B C SETTING ZERO_EN VCC VCC GND INT_THRS VCC GND VCC Enabled Enabled Disabled DEVICE FUNCTIONALITY ZERO CROSSING ADAPTIVE PEAK THRESHOLD Enabled Disabled Disabled
Table 3. MAX9927 Operating Modes
OPERATING MODE A1 B SETTING INT_THRS VCC GND Enabled Enabled DEVICE FUNCTIONALITY ZERO CROSSING ADAPTIVE PEAK THRESHOLD Enabled Disabled
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold
Differential Amplifier
The input operational amplifier is a rail-to-rail input and output precision amplifier with CMOS input bias currents, low offset voltage (VOS) and drift. A novel input architecture eliminates crossover distortion at the operational amplifier inputs normally found in rail-to-rail input structures. These features enable reliable small-signal detection for VR sensors. The MAX9924/MAX9926 include on-chip precisionmatched low-ppm resistors configured as a differential amplifier. High-quality matching and layout of these resistors produce extremely high DC and AC CMRR that is important to maintain noise immunity. The matched ppm-drift of the resistors guarantees performance across the entire -40C to +125C automotive temperature range.
Adaptive Peak Threshold
Modes A1 and A2 in the MAX9924-MAX9927 use an internal adaptive peak threshold voltage to trigger the output comparator. This adaptive peak threshold voltage scheme provides robust noise immunity to the input VR signal, preventing false triggers from occurring due to broken tooth or off-centered gear-tooth wheel. See Figure 1. The sensor signal at the output of the differential gain stage is used to generate a cycle-by-cycle adaptive peak threshold voltage. This threshold voltage is 1/3 of the peak of the previous cycle of the input VR signal. As the sensor signal peak voltage rises, the adaptive peak threshold voltage also increases by the same ratio. Conversely, decreasing peak voltage levels of the input VR signal causes the adaptive peak threshold voltage used to trigger the next cycle also to decrease to a new lower level. This threshold voltage then provides an arming level for the zero-crossing circuit of the comparator (see the Zero Crossing section). If the input signal voltage remains lower than the adaptive peak threshold for more than 85ms, an internal watchdog timer drops the threshold level to a default minimum threshold (VMIN_THRESH). This ensures pulse recognition recovers even in the presence of intermittent sensor connection. The internal adaptive peak threshold can be disabled and directly fed from the EXT input. This mode of operation is called Mode B, and allows implementations of custom threshold algorithms in firmware. This EXT voltage is typically generated by filtering a PWM-modulated output from an onboard microcontroller (C). An external operational amplifier can also be used to construct an active lowpass filter to filter the PWM-modulated EXT signal.
ADAPTIVE THRESHOLD SET BY V2
MAX9924-MAX9927
Bias Reference
In Modes A1, B, and C, a well-decoupled external resistor-divider generates a VCC/2 signal for the BIAS input that is used to reference all internal electronics in the device. BIAS should be bypassed with a 0.1F and 10F capacitor in parallel with the lower half of the resistor-divider forming a lowpass filter to provide a stable external BIAS reference. The minimum threshold, adaptive peak threshold, zerocrossing threshold signals are all referenced to this voltage. An input buffer eliminates loading of resistordividers due to differential amplifier operation. Connect BIAS to ground when operating in Mode A2. An internal (2.5V typical) reference is used in Mode A2, eliminating external components.
ADAPTIVE THRESHOLD SET BY V1 1 V1 3 VR SIGNAL V1 V2 1/3 V2
MIN THRESHOLD
65ms COUT
20ms
40ms
60ms
80ms
100ms
120ms
140ms
160ms
180ms
200ms
Figure 1. Adaptive Peak Threshold Operation
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Zero Crossing
The zero-crossing signal provides true timing information for engine-control applications. The zero-voltage level in the VR sensor signal corresponds to the center of the gear-tooth and is the most reliable marker for position/angle-sensing applications. Since the output of the differential amplifier is level-shifted to the BIAS voltage, the zero of the input VR signal is simply BIAS. The comparator output state controls the status of the input switch that changes the voltage at its noninverting input from the adaptive/external threshold level to the BIAS level. The difference in these two voltages then effectively acts as hysteresis for the comparator, thus providing noise immunity.
Rotational Direction Output (MAX9926 Only)
For quadrature-connected VR sensors, the open-drain output DIRN indicates the rotational direction of inputs IN1 and IN2 based on the output state of COUT1 and COUT2. DIRN goes high when COUT1 is leading COUT2, and low when COUT1 is following COUT2.
Applications Information
Bypassing and Layout Considerations
Good power-supply decoupling with high-quality bypass capacitors is always important for precision analog circuits. The use of an internal charge pump for the front-end amplifier makes this more important. Bypass capacitors create a low-impedance path to ground for noise present on the power supply. The minimum impedance of a capacitor is limited to the effective series resistance (ESR) at the self-resonance frequency, where the effective series inductance (ESL) cancels out the capacitance. The ESL of the capacitor dominates past the self-resonance frequency resulting in a rise in impedance at high frequencies. Bypass the power supply of the MAX9924-MAX9927 with multiple capacitor values in parallel to ground. The use of multiple values ensures that there will be multiple self-resonance frequencies in the bypass network, lowering the combined impedance over frequency. It is recommended to use low-ESR and low-ESL ceramic surface-mount capacitors in a parallel combination of 10nF, 0.1F and 1F, with the 10nF placed closest between the V CC and GND pins. The connection between these capacitor terminals and the power-supply pins of the part (both VCC and GND) should be through wide traces (preferably planes), and without vias in the high-frequency current path.
Comparator
The internal comparator is a fast open-drain output comparator with low input offset voltage and drift. The comparator precision affects the ability of the signal chain to resolve small VR sensor signals. An open-drain output allows the comparator to easily interface to a variety of C I/O voltages. When operating the MAX9924/MAX9925/MAX9926 in Mode C, external hysteresis can be provided by adding external resistors (see Figures 5 and 8). The high and low hysteresis thresholds in Mode C can be calculated using the following equations, R1(VPULLUP - VBIAS ) VTH = + VBIAS R1+ R2 + RPULLUP and R2 VTL = xV R1+ R2 BIAS
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Application Circuits
10k IN+
VPULLUP RPULLUP
VR SENSOR 10k
1nF COUT INBIAS TPU
C
MAX9924 MAX9926
EXT
10F || 0.1F
1k
1k +5V VCC ZERO_EN INT_THRS
GND
Figure 2. MAX9924/MAX9926 Operating Mode A1
10k IN+
VPULLUP RPULLUP
VR SENSOR 10k
1nF COUT INBIAS TPU
C
MAX9924 MAX9926
EXT
+5V
VCC ZERO_EN INT_THRS GND
Figure 3. MAX9924/MAX9926 Operating Mode A2
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15
Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Application Circuits (continued)
10k IN+ RPULLUP VR SENSOR 10k INBIAS 10F || 0.1F 1k 1k +5V VCC ZERO_EN INT_THRS GND 1nF COUT TPU PWM C VPULLUP
MAX9924 MAX9926
EXT FILTER
Figure 4. MAX9924/MAX9926 Operating Mode B
10k IN+
VPULLUP RPULLUP
VR SENSOR 10k
1nF COUT INBIAS TPU
C
MAX9924 MAX9926
EXT
R2
10F || 0.1F
1k
1k +5V VCC INT_THRS ZERO_EN
GND
R1
Figure 5. MAX9924/MAX9926 Operating Mode C
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Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold
Application Circuits (continued)
MAX9924-MAX9927
10k IN+ VR SENSOR 1nF 10k IN-
OUT
VPULLUP RPULLUP COUT TPU
C
MAX9925 MAX9927
BIAS 10F || 0.1F 1k +5V 1k VCC ZERO_EN INT_THRS GND EXT
Figure 6. MAX9925/MAX9927 Operating Mode A
10k IN+ VR SENSOR 1nF 10k IN-
OUT
VPULLUP RPULLUP COUT TPU PWM
C
MAX9925 MAX9927
BIAS 10F || 0.1F 1k +5V 1k VCC ZERO_EN INT_THRS GND EXT FILTER
Figure 7. MAX9925/MAX9927 Operating Mode B
______________________________________________________________________________________
17
Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Application Circuits (continued)
10k IN+ VR SENSOR 1nF 10k
OUT
VPULLUP RPULLUP COUT TPU
C
INBIAS 10F || 0.1F 1k 1k +5V VCC INT_THRS
MAX9925
R2
EXT
ZERO_EN
GND
R1
Figure 8. MAX9925 Operating Mode C
18
______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Typical Operating Circuit
4.5V TO 5.5V VCC VCC INVCC VR SENSOR IN+ 100k RPULLUP 100k COMPARATOR 85ms WATCHDOG COUT TPU C OP AMP 100k 100k
MAX9924
VPULLUP
BANDGAP REFERENCE VOLTAGE = 2 x VBG BUFFER
BIAS PEAK DETECTOR
30% VCC 10k VMIN THRESHOLD *THE MAX9924 IS CONFIGURED IN MODE A2. MODE LOGIC MODE LOGIC ZERO_EN
INT_THRS EXT
GND
______________________________________________________________________________________
19
Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Pin Configurations
TOP VIEW +
16 IN1+ 15 IN114 VCC
IN_THRS1 1 EXT1 2 BIAS1 3 COUT1 4 COUT2 5 BIAS2 6 EXT2 7 INT_THRS2 8
IN_THRS1 1 EXT1 2 BIAS1 3 COUT1 4 COUT2 5 BIAS2 6 EXT2 7 INT_THRS2 8
+
16 IN1+ 15 IN114 VCC
MAX9926
13 ZERO_EN 12 DIRN 11 GND 10 IN29 IN2+
MAX9927
13 OUT1 12 OUT2 11 GND 10 IN29 IN2+
QSOP
QSOP
TOP VIEW
IN+ 1 INN.C. BIAS GND 2 3 4 5
+
10 VCC 9 INT_THRS EXT COUT ZERO_EN
IN+ 1 INOUT BIAS GND 2 3 4 5
+
10 VCC 9 INT_THRS EXT COUT ZERO_EN
MAX9924
8 7 6
MAX9925
8 7 6
MAX
MAX
Chip Information
PROCESS: BiCMOS
20
______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE 10 MAX 16 QSOP PACKAGE CODE U10-2 E16-1 DOCUMENT NO. 21-0061 21-0055
10LUMAX.EPS
MAX9924-MAX9927
______________________________________________________________________________________
21
Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924-MAX9927
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
QSOP.EPS

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