MAX9924_11

19-4283; Rev 3; 3/11 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 µMAX ® package, while the MAX9926/MAX9927 are available in the 16-pin QSOP package. All devices are specified over the -40°C to +125°C automotive temperature range. Features o Differential Input Stage Provides Enhanced Noise Immunity o Precision Amplifier and Comparator Allows Small-Signal Detection o User-Enabled Internal Adaptive Peak Threshold or Flexible External Threshold o Zero-Crossing Detection Provides Accurate Phase Information MAX9924–MAX9927 Ordering Information PART MAX9924UAUB+ MAX9925AUB+ MAX9926UAEE+ MAX9927AEE+ TEMP RANGE -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C PIN-PACKAGE 10 µMAX 10 µMAX 16 QSOP 16 QSOP +Denotes a lead(Pb)-free/RoHS-compliant package. 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 µMAX 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 μC ________________________________________________________________ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 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 = +70°C) (Note 1) 10-Pin µMAX (derate 8.8mW/°C above +70°C) ........707.3mW 16-Pin QSOP (derate 9.6mW/°C above +70°C)........771.5mW Operating Temperature Range .........................-40°C to +125°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Soldering Temperature (reflow) .......................................+260°C 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. PACKAGE THERMAL CHARACTERISTICS (Note 1) µMAX Junction-to-Ambient Thermal Resistance (θJA) ......113.1°C/W Junction-to-Case Thermal Resistance (θJC) ................42°C/W QSOP Junction-to-Ambient Thermal Resistance (θJA) ......103.7°C/W Junction-to-Case Thermal Resistance (θJC) ................37°C/W 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. ELECTRICAL CHARACTERISTICS (VCC = 5V, VGND = 0V, MAX9925/MAX9927 gain setting = 1V/V, Mode A1, VBIAS = 2.5V, VPULLUP = 5V, RPULLUP = 1kΩ, CCOUT = 50pF. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (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 ~ 1µs Guaranteed by CMRR Temperature drift 0.5 (Note 4) (Note 4) From VCM = 0 to VCC MAX9925 MAX9927 Output Voltage Low Output Voltage High Recovery Time from Saturation Gain-Bandwidth Product Slew Rate Charge-Pump Frequency VOL VOH tSAT GBW SR fCP IOL = 1mA IOH = -1mA To 1% of the actual VOUT after output saturates VCC 0.050 1.2 1.4 2.3 1.3 75 88 77 0.1 0.05 102 105 94 0.050 V V µs MHz V/µs MHz 0 4.5 2.6 4.7 30 5.5 5 10 150 V mA µs 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 IN+, INVOS-OA IBIAS IOFFSET CMRR PSRR VCC 5 3 6 2 V µV/°C mV nA nA dB dB 2 _______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold ELECTRICAL CHARACTERISTICS (continued) (VCC = 5V, VGND = 0V, MAX9925/MAX9927 gain setting = 1V/V, Mode A1, VBIAS = 2.5V, VPULLUP = 5V, RPULLUP = 1kΩ, CCOUT = 50pF. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX VCC + 0.3 87 78 100 135 UNITS MAX9924–MAX9927 INPUT DIFFERENTIAL AMPLIFIER (MAX9924/MAX9926) Input Voltage Range Differential Amplifier Common-Mode Rejection Ratio Input Resistance ADAPTIVE PEAK DETECTION Mode B operation (Notes 5, 6) MAX9924/MAX9925 MAX9926/MAX9927 -6.5 -6.5 0 0 33 4 15 30 +6.5 mV +10 %PK IN+, INCMRR RIN Guaranteed by CMRR MAX9924 (Note 5) MAX9926 (Note 5) (Note 5) -0.3 60 55 65 V dB kΩ Zero-Crossing Threshold VZERO_THRESH VADAPTIVE Adaptive peak threshold Minimum threshold of hysteresis comparator MAX9924/MAX9926 (Notes 5, 6) Minimum threshold of hysteresis comparator MAX9925/MAX9927 (Notes 5, 6) 20 30 50 mV Fixed and Adaptive Peak Threshold VMIN-THRESH VMIN-THRESH - VZERO-THRESH for MAX9924 (Notes 5, 6) VMIN-THRESH - VZERO-THRESH for MAX9926 (Notes 5, 6) VMIN-THRESH - VZERO-THRESH for MAX9925/MAX9927 (Notes 5, 6) 7 2 19 15 15 30 26 30 50 Watchdog Timeout for Adaptive Peak Threshold ENTIRE SYSTEM Comparator Output Low Voltage Propagation Delay COUT Transition Time Propagation Delay Jitter tWD Timing window to reset the adaptive peak threshold if not triggered (input level below threshold) 45 85 140 ms 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 0.2 V ns ns ns _______________________________________________________________________________________ 3 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924–MAX9927 ELECTRICAL CHARACTERISTICS (continued) (VCC = 5V, VGND = 0V, MAX9925/MAX9927 gain setting = 1V/V, Mode A1, VBIAS = 2.5V, VPULLUP = 5V, RPULLUP = 1kΩ, CCOUT = 50pF. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2) PARAMETER EXT Mode B, TA = +125°C EXT Voltage Range VEXT Mode C, TA = +125°C Input Current to EXT 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 IBIAS Modes A1, A2, B, C Modes A1, B, TA = +125°C BIAS Voltage Range VBIAS Mode C, TA = +125°C Internal BIAS Reference Voltage VINT_BIAS Mode A2 (MAX9924/MAX9926) 0.2 2.46 1.5 1 VCC - 1.1 VCC - 1.1 V µA VIL VIH ILEAK ISINK Pullup resistor = 10kΩ, VZERO_EN = VGND 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 µA µA 0.2 V IEXT Mode B, VEXT > VBIAS; and Mode C 0.14 1.5 VCC - 1.1 V VCC - 1.1 10 µA SYMBOL CONDITIONS MIN TYP MAX UNITS tSW 3 µs V Note 2: Note 3: Note 4: Note 5: Note 6: Specifications are 100% tested at TA = +125°C, 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. 4 _______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold Typical Operating Characteristics (VCC = 5V, VGND = 0V, MAX9925/MAX9927 gain setting = 1V/V. All values are at TA = +25°C, 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 (μV) 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) _______________________________________________________________________________________ 5 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924–MAX9927 Typical Operating Characteristics (continued) (VCC = 5V, VGND = 0V, MAX9925/MAX9927 gain setting = 1V/V. All values are at TA = +25°C, 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 COUT 5V INPUT SIGNAL 833mV VBIAS fIN = 1kHz 100μs/div 100μs/div DIRN OPERATION (MAX9924) MAX9924 toc15 INPUT REFERRED NOISE DENSITY vs. FREQUENCY 100 INPUT VOLTAGE NOISE (nV/ Hz) MAX9924 toc16 80 60 40 20 200μs/div 10 10 100 1k 10k 100k 1M FREQUENCY (Hz) 6 _______________________________________________________________________________________ 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 0.1µF and 10µF capacitor. Ground Zero-Crossing Enable. Mode configuration pin, internally pulled up to VCC with 10kΩ resistor. Comparator Output. Open-drain output, connect a 10kΩ 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 0.1µF and 10µF capacitor. Comparator Output 1. Open-drain output, connect a 10kΩ pullup resistor from COUT1 to VPULLUP. Comparator Output 2. Open-drain output, connect a 10kΩ pullup resistor from COUT2 to VPULLUP. Input Bias 2. Connect to an external resistor-divider and bypass to ground with a 0.1µF and 10µF 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 _______________________________________________________________________________________ 7 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924–MAX9927 Functional Diagrams VCC 100kΩ INVCC 100kΩ IN+ 100kΩ 100kΩ VCC MAX9924 OP AMP GND COMPARATOR 65ms WATCHDOG COUT INTERNAL REFERENCE 2.5V BUFFER 30% BIAS PEAK DETECTOR VMIN THRESHOLD MODE LOGIC MODE LOGIC VCC 10kΩ ZERO_EN INT_THRS INT_THRS EXT 8 _______________________________________________________________________________________ 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 10kΩ ZERO_EN INT_THRS EXT _______________________________________________________________________________________ 9 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924–MAX9927 Functional Diagrams (continued) VCC 100kΩ IN1VCC 100kΩ IN1+ 100kΩ COMPARATOR 85ms WATCHDOG COUT1 OP AMP 100kΩ VCC MAX9926 GND INTERNAL REFERENCE 2.5V BUFFER 30% BIAS1 PEAK DETECTOR VMIN THRESHOLD CLK DIRN FLIP-FLOP DIRN EXT1 VCC 100kΩ IN2VCC 100kΩ IN2+ 100kΩ COMPARATOR 85ms WATCHDOG COUT2 OP AMP 100kΩ BUFFER 30% BIAS2 PEAK DETECTOR VMIN THRESHOLD VCC 10kΩ MODE LOGIC ZERO_EN INT_THRS1 INT_THRS2 EXT2 10 ______________________________________________________________________________________ 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 ______________________________________________________________________________________ 11 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 12 ______________________________________________________________________________________ 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 -40°C to +125°C 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 (µC). 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 0.1µF and 10µF 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 85ms COUT 20ms 40ms 60ms 80ms 100ms 120ms 140ms 160ms 180ms 200ms Figure 1. Adaptive Peak Threshold Operation ______________________________________________________________________________________ 13 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, 0.1µF and 1µF, 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 µC 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 = ⎜ ⎟ ×V ⎝ R1+ R2 ⎠ BIAS 14 ______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924–MAX9927 Application Circuits 10kΩ IN+ RPULLUP VR SENSOR 10kΩ INBIAS 10μF || 0.1μF 1kΩ 1kΩ +5V VCC ZERO_EN INT_THRS GND 1nF COUT TPU μC VPULLUP MAX9924 MAX9926 EXT Figure 2. MAX9924/MAX9926 Operating Mode A1 10kΩ IN+ VPULLUP RPULLUP VR SENSOR 10kΩ 1nF COUT INBIAS TPU μC MAX9924 MAX9926 EXT +5V VCC ZERO_EN INT_THRS GND Figure 3. MAX9924/MAX9926 Operating Mode A2 ______________________________________________________________________________________ 15 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924–MAX9927 Application Circuits (continued) 10kΩ IN+ RPULLUP VR SENSOR 10kΩ INBIAS 10μF || 0.1μF 1kΩ 1kΩ +5V VCC ZERO_EN INT_THRS GND 1nF COUT TPU PWM μC VPULLUP MAX9924 MAX9926 EXT FILTER Figure 4. MAX9924/MAX9926 Operating Mode B 10kΩ IN+ VPULLUP RPULLUP VR SENSOR 10kΩ 1nF COUT INBIAS TPU μC MAX9924 MAX9926 EXT R2 10μF || 0.1μF 1kΩ 1kΩ +5V VCC INT_THRS ZERO_EN GND R1 Figure 5. MAX9924/MAX9926 Operating Mode C 16 ______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold Application Circuits (continued) MAX9924–MAX9927 10kΩ INVR SENSOR 1nF 10kΩ IN+ OUT VPULLUP RPULLUP COUT TPU μC MAX9925 MAX9927 BIAS 10μF || 0.1μF 1kΩ +5V 1kΩ VCC ZERO_EN INT_THRS GND EXT Figure 6. MAX9925/MAX9927 Operating Mode A 10kΩ INVR SENSOR 1nF 10kΩ IN+ OUT VPULLUP RPULLUP COUT TPU PWM μC MAX9925 MAX9927 BIAS 10μF || 0.1μF 1kΩ +5V 1kΩ 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) 10kΩ INVR SENSOR 1nF 10kΩ OUT VPULLUP RPULLUP COUT TPU μC IN+ BIAS 10μF || 0.1μF 1kΩ 1kΩ +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+ 100kΩ OP AMP 100kΩ 100kΩ MAX9924 VPULLUP RPULLUP μC TPU 100kΩ COMPARATOR 85ms WATCHDOG COUT BANDGAP REFERENCE VOLTAGE = 2 x VBG BUFFER BIAS PEAK DETECTOR 30% VCC 10kΩ 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 μMAX μMAX 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 (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE 10 µMAX 16 QSOP PACKAGE CODE U10+2 E16+1 OUTLINE NO. 21-0061 21-0055 LAND PATTERN NO. 90-0330 90-0167 10LUMAX.EPS MAX9924–MAX9927 α α ______________________________________________________________________________________ 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 (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. 22 ______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold Revision History REVISION NUMBER 0 1 2 3 REVISION DATE 10/08 2/09 3/09 3/11 Initial release Removed future product references for the MAX9926 and MAX9927, updated EC table Corrected various errors Updated Figures 6, 7, and 8 DESCRIPTION PAGES CHANGED — 1–4 2, 3, 4, 6, 13 17, 18 MAX9924–MAX9927 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 23 © 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.