19-4283; Rev 2; 3/09 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold 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. Applications 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 Ordering Information PART TEMP RANGE MAX9924UAUB+ -40°C to +125°C 10 µMAX PIN-PACKAGE MAX9925AUB+ -40°C to +125°C 10 µMAX MAX9926UAEE+ -40°C to +125°C 16 QSOP MAX9927AEE+ -40°C to +125°C 16 QSOP +Denotes a lead(Pb)-free/RoHS-compliant package. Selector Guide PART AMPLIFIER GAIN MAX9924UAUB 1 x Differential 1V/V MAX9925AUB 1 x Operational Externally Set MAX9926UAEE 2 x Differential 1V/V MAX9927AEE 2 x Operational Externally Set Camshaft VRS Interfaces Crankshaft VRS Interfaces µMAX is a registered trademark of Maxim Integrated Products, Inc. Vehicle Speed VRS Interfaces Simplified Block Diagram ENGINE BLOCK MAX9924 VR SENSOR DIFFERENTIAL AMPLIFIER ADAPTIVE/MINIMUM AND ZERO-CROSSING THRESHOLDS μC INTERNAL/EXTERNAL BIAS VOLTAGE ________________________________________________________________ Maxim Integrated Products 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. 1 MAX9924–MAX9927 General Description MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold 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 Junction-to-Case Thermal Resistance (θJC) (Note 1) 10-Pin µMAX.................................................................42°C/W 16-Pin QSOP ................................................................37°C/W Junction-to-Ambient Thermal Resistance (θJA) (Note 1) 10-Pin µMAX............................................................113.1°C/W 16-Pin QSOP ...........................................................103.7°C/W 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 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 = 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 UNITS 5.5 V POWER SUPPLY Operating Supply Range VCC Supply Current ICC Power-On Time PON (Note 3) 4.5 MAX9924/MAX9925 2.6 5 MAX9926/MAX9927 4.7 10 VCC > VUVLO = 4.1V, step time for VCC ~ 1µs 30 150 mA µs INPUT OPERATIONAL AMPLIFIER (MAX9925/MAX9927) Input Voltage Range Input Offset Voltage Input Bias Current IN+, INVOS-OA Guaranteed by CMRR 0 Temperature drift 0.5 VCC V 5 µV/°C 3 mV IBIAS (Note 4) 0.1 6 nA Input Offset Current IOFFSET (Note 4) 0.05 2 nA Common-Mode Rejection Ratio CMRR From VCM = 0 to VCC 75 102 Power-Supply Rejection Ratio PSRR MAX9925 88 105 MAX9927 77 94 Output Voltage Low VOL IOL = 1mA Output Voltage High VOH IOH = -1mA Recovery Time from Saturation tSAT To 1% of the actual VOUT after output saturates Gain-Bandwidth Product dB dB 0.050 VCC 0.050 V V 1.2 µs GBW 1.4 MHz Slew Rate SR 2.3 V/µs Charge-Pump Frequency fCP 1.3 MHz 2 _______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold (VCC = 5V, VGND = 0, 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 UNITS VCC + 0.3 V INPUT DIFFERENTIAL AMPLIFIER (MAX9924/MAX9926) Input Voltage Range Differential Amplifier Common-Mode Rejection Ratio Input Resistance IN+, INCMRR RIN Guaranteed by CMRR -0.3 MAX9924 (Note 5) 60 87 MAX9926 (Note 5) 55 78 (Note 5) 65 100 135 MAX9924/MAX9925 -6.5 0 +6.5 MAX9926/MAX9927 -6.5 0 +10 dB kΩ ADAPTIVE PEAK DETECTION Zero-Crossing Threshold VZERO_THRESH VADAPTIVE Fixed and Adaptive Peak Threshold Watchdog Timeout for Adaptive Peak Threshold VMIN-THRESH tWD Mode B operation (Notes 5, 6) mV Adaptive peak threshold 33 %PK Minimum threshold of hysteresis comparator MAX9924/MAX9926 (Notes 5, 6) 4 15 30 Minimum threshold of hysteresis comparator MAX9925/MAX9927 (Notes 5, 6) 20 30 50 VMIN-THRESH - VZERO-THRESH for MAX9924 (Notes 5, 6) 7 15 26 VMIN-THRESH - VZERO-THRESH for MAX9926 (Notes 5, 6) 2 15 30 VMIN-THRESH - VZERO-THRESH for MAX9925/MAX9927 (Notes 5, 6) 19 30 50 Timing window to reset the adaptive peak threshold if not triggered (input level below threshold) 45 85 140 ms 0.2 V mV ENTIRE SYSTEM Comparator Output Low Voltage Propagation Delay COUT Transition Time Propagation Delay Jitter VCOUT_OL tPDZ Overdrive = 2V to 3V, zero-crossing 50 tPDA Overdrive = 2V to 3V, adaptive peak 150 tHL-LH tPD-JITTER Includes noise of differential amplifier and comparator, f = 10kHz, VIN = 1VP-P sine wave ns 2 ns 20 ns _______________________________________________________________________________________ 3 MAX9924–MAX9927 ELECTRICAL CHARACTERISTICS (continued) MAX9924–MAX9927 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 = 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 UNITS EXT EXT Voltage Range Input Current to EXT Mode B, TA = +125°C 1.5 VCC - 1.1 Mode C, TA = +125°C 0.14 VCC - 1.1 V VEXT IEXT Mode B, VEXT > VBIAS; and Mode C 10 µA 0.2 V 0.3 x VCC V DIRN (MAX9926 Only) Output Low Voltage INT_THRS, ZERO_EN Low Input VIL High Input VIH Input Leakage ILEAK Input Current ZERO_EN ISINK Switching Time Between Modes A1, A2, and Modes B, C tSW 0.7 x VCC Pullup resistor = 10kΩ, VZERO_EN = GND V 500 With INT_THRS = GND, auto peakdetect is disabled, and EXT_THRS is active 1 µA 800 µA 3 µs BIAS Input Current to BIAS BIAS Voltage Range Internal BIAS Reference Voltage Note 2: Note 3: Note 4: Note 5: Note 6: 4 IBIAS Modes A1, A2, B, C 1 Modes A1, B, TA = +125°C 1.5 VCC - 1.1 Mode C, TA = +125°C 0.2 VCC - 1.1 VBIAS VINT_BIAS Mode A2 (MAX9924/MAX9926) 2.46 µA V V 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. _______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold INPUT OFFSET VOLTAGE vs. INPUT COMMON-MODE VOLTAGE 10 5 120 0.4 100 80 0.3 CMRR (dB) 15 0.5 MAX9924 toc02 0.2 40 0.1 0 -0.5 3.5 4.5 0 5.5 1 100 100 -80 -90 10k 100k VOL AND VOH vs. TEMPERATURE MAX9924 toc06 VCC = 5V VBIAS = 2.5V VOUT = 2VP-P MAX9925 1k 40 35 30 VOL AND VOH (mV) -60 -70 10 FREQUENCY (Hz) MAX9924 toc05 MAX9924 toc04 125 GAIN (dB) PSSR (dB) -40 -50 75 50 25 VCC - VOH 20 VOL 15 10 25 -100 -110 5 -120 1 10 100 1k 10k 0 0 0.001 100k 0.3 VCM = 2.5V 0.2 0.1 800 700 500 400 300 25 50 75 TEMPERATURE (°C) 100 125 100 350 125 250 200 150 100 200 0 0.5 1.0 1.5 SIGNAL LEVEL (VP) 2.0 VIN = 2VP-P fIN = 1kHz MAX9924 50 fIN = 1kHz MAX9924 0 0 0 75 300 600 100 0 50 400 THRESHOLD (mV) VCM = 0 25 ADAPTIVE THRESHOLD vs. TEMPERATURE MAX9924 toc08 0.5 900 ADAPTIVE THRESHOLD LEVEL (mV) VOUT = 2.5V MAX9925 -25 0 TEMPERATURE (°C) ADAPTIVE THRESHOLD AND RATIO vs. SIGNAL LEVEL MAX9924 toc07 0.6 -50 -25 FREQUENCY (kHz) INPUT OFFSET VOLTAGE vs. TEMPERATURE 0.4 -50 10 0.1 FREQUENCY (Hz) INPUT OFFSET VOLTAGE (mV) 2.5 OPEN LOOP FREQUENCY RESPONSE VRIPPLE = 100mVP-P VBIAS = VOUT = 2.5V INPUTS COUPLED TO GND -20 -30 1.5 INPUT COMMON-MODE VOLTAGE (V) POWER-SUPPLY REJECTION RATIO vs. FREQUENCY 0 -10 0.5 VBIAS = VOUT = 2.5V VCM = 2VP-P CMRR = 20log(ADM/ACM) 20 VOUT = 2.5V MAX9925 0 0 2000 3000 -2000 -1000 1000 -500 500 1500 2500 -1500 INPUT OFFSET VOLTAGE (μV) 60 MAX9924 toc09 PERCENTAGE OF UNITS (%) VCM = 0 BIN SIZE = 250 INPUT OFFSET VOLTAGE (mV) MAX9924 toc01 20 COMMON-MODE REJECTION RATIO vs. FREQUENCY MAX9924 toc03 INPUT OFFSET VOLTAGE DISTRIBUTION 2.5 -50 -25 0 25 50 75 100 125 TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX9924–MAX9927 Typical Operating Characteristics (VCC = 5V, VGND = 0, MAX9925/MAX9927 gain setting = 1V/V. All values are at TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VCC = 5V, VGND = 0, MAX9925/MAX9927 gain setting = 1V/V. All values are at TA = +25°C, unless otherwise noted.) MINIMUM AND ZERO-CROSSING THRESHOLD vs. TEMPERATURE MINIMUM THRESHOLD MAX9924 toc11 25 MAX9924 toc12 100 MAX9924 toc10 VCM = 2.5V fIN = 5Hz INPUT SIGNAL vs. COUT WITH WATCHDOG TIMER EXPIRED CMRR vs. TEMPERATURE 30 COUT INPUT SIGNAL 5V 75 20 CMRR (dB) THRESHOLD (mV) 15 10 ZERO CROSSING AT 5Hz ZERO CROSSING AT 1Hz 5 50 VBIAS 25 0 MAX9924 VCM = 0 TO 5V -5 fIN = 5Hz 0 -50 -25 0 25 50 75 100 125 -50 -25 TEMPERATURE (°C) 0 25 50 75 100 125 20ms/div TEMPERATURE (°C) OVERDRIVEN INPUT VOLTAGES (MAX9924) INPUT SIGNAL vs. COUT WITH WATCHDOG TIMER EXPIRED MAX9924 toc13 COUT MAX9924 toc14 INPUT SIGNAL 5V 833mV VBIAS fIN = 1kHz 100μs/div 100μs/div DIRN OPERATION (MAX9924) INPUT REFERRED NOISE DENSITY vs. FREQUENCY MAX9924 toc15 MAX9924 toc16 100 INPUT VOLTAGE NOISE (nV/ Hz) MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold 80 60 40 20 10 200μs/div 10 100 1k 10k 100k 1M FREQUENCY (Hz) 6 _______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold PIN NAME FUNCTION MAX9924 MAX9925 MAX9926 MAX9927 1 1 — — IN+ Noninverting Input 2 2 — — IN- Inverting Input — 3 — — OUT Amplifier Output 3 — — — N.C. No Connection. Not internally connected. 4 4 — — BIAS Input Bias. Connect to an external resistor-divider and bypass to ground with a 0.1µF and 10µF capacitor. 5 5 11 11 GND Ground 6 6 13 — ZERO_EN 7 7 — — COUT 8 8 — — EXT 9 9 — — INT_THRS 10 10 14 14 VCC — — 1 1 INT_THRS1 — — 2 2 EXT1 External Reference Input 1. Leave EXT unconnected in Modes A1, A2. Apply an external voltage in Modes B, C. — — 3 3 BIAS1 Input Bias 1. Connect to an external resistor-divider and bypass to ground with a 0.1µF and 10µF capacitor. — — 4 4 COUT1 Comparator Output 1. Open-drain output, connect a 10kΩ pullup resistor from COUT1 to VPULLUP. — — 5 5 COUT2 Comparator Output 2. Open-drain output, connect a 10kΩ pullup resistor from COUT2 to VPULLUP. — — 6 6 BIAS2 Input Bias 2. Connect to an external resistor-divider and bypass to ground with a 0.1µF and 10µF capacitor. — — 7 7 EXT2 External Reference Input 2. Leave EXT unconnected in Modes A1, A2. Apply an external voltage in Modes B, C. — — 8 8 INT_THRS2 — — 9 9 IN2+ Noninverting Input 2 — — 10 10 IN2- Inverting Input 2 — — 12 — DIRN Rotational Direction Output. Open-drain output, connect a pullup resistor from DIRN to VPULLUP. — — — 12 OUT2 Amplifier Output 2 — — — 13 OUT1 — — 15 15 IN1- Noninverting Input 1 — — 16 16 IN1+ Inverting Input 1 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. Internal Adaptive Threshold 2. Mode configuration pin. Amplifier Output 1 _______________________________________________________________________________________ 7 MAX9924–MAX9927 Pin Description MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold Functional Diagrams 100kΩ VCC VCC 100kΩ IN- VCC MAX9924 GND OP AMP 100kΩ IN+ 100kΩ COMPARATOR 85ms WATCHDOG COUT INTERNAL REFERENCE 2.5V BUFFER 30% VCC BIAS PEAK DETECTOR 10kΩ VMIN THRESHOLD MODE LOGIC MODE LOGIC INT_THRS 8 EXT _______________________________________________________________________________________ ZERO_EN INT_THRS Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold OUT VCC IN- VCC VCC MAX9925 GND OP AMP IN+ COMPARATOR BIAS 85ms WATCHDOG COUT BUFFER 30% VCC PEAK DETECTOR 10kΩ VMIN THRESHOLD MODE LOGIC ZERO_EN INT_THRS EXT _______________________________________________________________________________________ 9 MAX9924–MAX9927 Functional Diagrams (continued) Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924–MAX9927 Functional Diagrams (continued) 100kΩ VCC VCC 100kΩ IN1- VCC MAX9926 GND OP AMP 100kΩ IN1+ 100kΩ 85ms WATCHDOG COMPARATOR COUT1 INTERNAL REFERENCE 2.5V BUFFER 30% BIAS1 PEAK DETECTOR CLK VMIN THRESHOLD DIRN DIRN FLIP-FLOP EXT1 100kΩ VCC 100kΩ IN2- VCC OP AMP 100kΩ IN2+ 100kΩ COMPARATOR 85ms WATCHDOG COUT2 BUFFER 30% VCC BIAS2 PEAK DETECTOR 10kΩ VMIN THRESHOLD MODE LOGIC EXT2 10 ______________________________________________________________________________________ ZERO_EN INT_THRS1 INT_THRS2 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold OUT1 VCC IN1- VCC VCC MAX9927 GND OP AMP IN1+ COMPARATOR BIAS1 85ms WATCHDOG COUT1 BUFFER 30% PEAK DETECTOR VMIN THRESHOLD EXT1 VCC IN2- VCC OUT1 OP AMP IN2+ COMPARATOR BIAS2 85ms WATCHDOG COUT2 BUFFER 30% MODE LOGIC PEAK DETECTOR INT_THRS1 INT_THRS2 VMIN THRESHOLD EXT2 ______________________________________________________________________________________ 11 MAX9924–MAX9927 Functional Diagrams (continued) MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold Detailed Description ing 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). 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. 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). 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 compar- Table 1. MAX9924/MAX9926 Operating Modes SETTING OPERATING MODE ZERO_EN DEVICE FUNCTIONALITY INT_THRS ZERO CROSSING ADAPTIVE PEAK THRESHOLD BIAS VOLTAGE SOURCE A1 VCC VCC Enabled Enabled External A2 GND GND Enabled Enabled Internal Ref B VCC GND Enabled Disabled External C GND VCC Disabled Disabled External Table 2. MAX9925 Operating Modes OPERATING MODE SETTING DEVICE FUNCTIONALITY ZERO_EN INT_THRS ZERO CROSSING ADAPTIVE PEAK THRESHOLD VCC VCC Enabled Enabled B VCC GND Enabled Disabled C GND VCC Disabled Disabled A1 Table 3. MAX9927 Operating Modes OPERATING MODE 12 SETTING DEVICE FUNCTIONALITY INT_THRS ZERO CROSSING ADAPTIVE PEAK THRESHOLD A1 VCC Enabled Enabled B GND Enabled Disabled ______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold 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. 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. 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 ADAPTIVE THRESHOLD SET BY V1 1 V1 3 VR SIGNAL MIN THRESHOLD V2 V1 1/3 V2 85ms COUT 20ms 40ms 60ms 80ms 100ms 120ms 140ms 160ms 180ms 200ms Figure 1. Adaptive Peak Threshold Operation ______________________________________________________________________________________ 13 MAX9924–MAX9927 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. MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold 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. 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 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. ______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold VPULLUP 10kΩ IN+ RPULLUP VR SENSOR μC 1nF COUT 10kΩ TPU INBIAS 10μF || 0.1μF 1kΩ MAX9924 MAX9926 1kΩ EXT VCC +5V ZERO_EN INT_THRS GND Figure 2. MAX9924/MAX9926 Operating Mode A1 VPULLUP 10kΩ IN+ RPULLUP VR SENSOR μC 1nF COUT 10kΩ TPU INBIAS MAX9924 MAX9926 EXT +5V VCC ZERO_EN INT_THRS GND Figure 3. MAX9924/MAX9926 Operating Mode A2 ______________________________________________________________________________________ 15 MAX9924–MAX9927 Application Circuits Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924–MAX9927 Application Circuits (continued) VPULLUP 10kΩ IN+ RPULLUP VR SENSOR μC 1nF TPU COUT 10kΩ INBIAS 1kΩ 10μF || 0.1μF 1kΩ +5V PWM MAX9924 MAX9926 EXT FILTER VCC ZERO_EN INT_THRS GND Figure 4. MAX9924/MAX9926 Operating Mode B VPULLUP 10kΩ IN+ RPULLUP VR SENSOR μC 1nF COUT 10kΩ TPU INBIAS 10μF || 0.1μF 1kΩ MAX9924 MAX9926 1kΩ +5V R2 EXT 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 10kΩ IN+ VR SENSOR VPULLUP OUT RPULLUP 1nF μC 10kΩ COUT IN- TPU MAX9925 MAX9927 BIAS 1kΩ 10μF || 0.1μF EXT 1kΩ VCC +5V ZERO_EN INT_THRS GND Figure 6. MAX9925/MAX9927 Operating Mode A 10kΩ IN+ VR SENSOR VPULLUP OUT RPULLUP 1nF μC 10kΩ COUT IN- TPU PWM MAX9925 MAX9927 BIAS 10μF || 0.1μF 1kΩ EXT 1kΩ +5V FILTER VCC ZERO_EN INT_THRS GND Figure 7. MAX9925/MAX9927 Operating Mode B ______________________________________________________________________________________ 17 MAX9924–MAX9927 Application Circuits (continued) Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924–MAX9927 Application Circuits (continued) 10kΩ IN+ VR SENSOR VPULLUP OUT RPULLUP 1nF μC 10kΩ COUT IN- MAX9925 TPU R2 BIAS 10μF || 0.1μF 1kΩ EXT 1kΩ +5V VCC INT_THRS ZERO_EN GND R1 Figure 8. MAX9925 Operating Mode C 18 ______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold 4.5V TO 5.5V VCC 100kΩ VCC 100kΩ INVCC MAX9924 VR SENSOR VPULLUP OP AMP IN+ 100kΩ μC RPULLUP 100kΩ COMPARATOR 85ms WATCHDOG COUT TPU BANDGAP REFERENCE VOLTAGE = 2 x VBG BUFFER 30% BIAS VCC PEAK DETECTOR 10kΩ VMIN THRESHOLD *THE MAX9924 IS CONFIGURED IN MODE A2. ZERO_EN MODE LOGIC MODE LOGIC GND INT_THRS EXT ______________________________________________________________________________________ 19 MAX9924–MAX9927 Typical Operating Circuit Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold MAX9924–MAX9927 Pin Configurations TOP VIEW IN_THRS1 1 + 16 IN1+ IN_THRS1 1 + 16 IN1+ EXT1 2 15 IN1- EXT1 2 15 IN1- BIAS1 3 14 VCC BIAS1 3 14 VCC MAX9926 COUT1 4 MAX9927 13 ZERO_EN COUT1 4 COUT2 5 12 DIRN COUT2 5 12 OUT2 BIAS2 6 11 GND BIAS2 6 11 GND EXT2 7 10 IN2- EXT2 7 10 IN2- IN2+ INT_THRS2 8 9 INT_THRS2 8 13 OUT1 9 QSOP IN2+ QSOP TOP VIEW IN+ 1 IN- 2 N.C. 3 BIAS GND + 10 VCC 9 INT_THRS 8 4 5 MAX9924 IN+ 1 IN- 2 EXT OUT 3 7 COUT BIAS 6 ZERO_EN GND + 10 VCC 9 INT_THRS 8 EXT 4 7 COUT 5 6 ZERO_EN μMAX MAX9925 μMAX Chip Information PROCESS: BiCMOS 20 ______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold PACKAGE CODE DOCUMENT NO. 10 µMAX U10-2 21-0061 16 QSOP E16-1 21-0055 10LUMAX.EPS PACKAGE TYPE α α ______________________________________________________________________________________ 21 MAX9924–MAX9927 Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Package Information (continued) For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. QSOP.EPS MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold 22 ______________________________________________________________________________________ Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold REVISION NUMBER REVISION DATE 0 10/08 Initial release 1 2/09 Removed future product references for the MAX9926 and MAX9927, updated EC table 2 3/09 Corrected various errors DESCRIPTION PAGES CHANGED — 1–4 2, 3, 4, 6, 13 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 © 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX9924–MAX9927 Revision History