General Description
The MAX9924–MAX9927 variable reluctance (VR or mag-
netic coil) sensor interface devices are ideal for position
and speed sensing for automotive crankshafts,
camshafts, transmission shafts, etc. These devices inte-
grate 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 ter-
minals of the internal operational amplifier available,
allowing greater flexibility for gain. The MAX9926 also
provides a direction output that is useful for quadrature-
connected VR sensors that are used in certain high-per-
formance 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 temper-
ature range.
Applications
Camshaft VRS Interfaces
Crankshaft VRS Interfaces
Vehicle Speed VRS Interfaces
Features
oDifferential Input Stage Provides Enhanced Noise
Immunity
oPrecision Amplifier and Comparator Allows
Small-Signal Detection
oUser-Enabled Internal Adaptive Peak Threshold or
Flexible External Threshold
oZero-Crossing Detection Provides Accurate
Phase Information
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-4283; Rev 4; 3/12
For pricing, delivery, and ordering information,please contact Maxim Directat 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
PART TEMP RANGE PIN-PACKAGE
MAX9924UAUB+ -40°C to +125°C 10 µMAX
MAX9924UAUB/V+ -40°C to +125°C 10 µMAX
MAX9925AUB+ -40°C to +125°C 10 µMAX
MAX9926UAEE+ -40°C to +125°C 16 QSOP
MAX9926UAEE/V+ -40°C to +125°C 16 QSOP
MAX9927AEE+ -40°C to +125°C 16 QSOP
MAX9927AEE/V+ -40°C to +125°C 16 QSOP
+
Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
Simplified Block Diagram
μC
DIFFERENTIAL
AMPLIFIER
ADAPTIVE/MINIMUM
AND
ZERO-CROSSING
THRESHOLDS
INTERNAL/EXTERNAL
BIAS VOLTAGE
VR SENSOR
ENGINE BLOCK
MAX9924
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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)
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.
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
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
POWER SUPPLY
Operating Supply Range VCC (Note 3) 4.5 5.5 V
MAX9924/MAX9925 2.6 5
Supply Current ICC MAX9926/MAX9927 4.7 10 mA
Power-On Time PON VCC > VUVLO = 4.1V, step time for VCC
~ 1µs 30 150 µs
INPUT OPERATIONAL AMPLIFIER (MAX9925/MAX9927)
Input Voltage Range IN+, IN- Guaranteed by CMRR 0 VCC V
Temperature drift 5 µV/°C
Input Offset Voltage VOS-OA 0.5 3 mV
Input Bias Current 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 dB
MAX9925 88 105
Power-Supply Rejection Ratio PSRR MAX9927 77 94 dB
Output Voltage Low VOL IOL = 1mA 0.050 V
Output Voltage High VOH IOH = -1mA VCC -
0.050 V
Recovery Time from Saturation tSAT To 1% of the actual VOUT after output
saturates 1.2 µs
Gain-Bandwidth Product GBW 1.4 MHz
Slew Rate SR 2.3 V/µs
Charge-Pump Frequency fCP 1.3 MHz
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.
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
PACKAGE THERMAL CHARACTERISTICS (Note 1)
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
_______________________________________________________________________________________ 3
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
INPUT DIFFERENTIAL AMPLIFIER (MAX9924/MAX9926)
Input Voltage Range IN+, IN- Guaranteed by CMRR -0.3 VCC +
0.3 V
MAX9924 (Note 5) 60 87
Differential Amplifier
Common-Mode Rejection Ratio CMRR MAX9926 (Note 5) 55 78 dB
Input Resistance RIN (Note 5) 65 100 135 kΩ
ADAPTIVE PEAK DETECTION
MAX9924/MAX9925 -6.5 0 +6.5
Zero-Crossing Threshold VZERO_THRESH
Mode B
operation
(Notes 5, 6) MAX9926/MAX9927 -6.5 0 +10
mV
VADAPTIVE Adaptive peak threshold 33 %PK
Minimum threshold of hysteresis
comparator MAX9924/MAX9926
(Notes 5, 6)
41530
Minimum threshold of hysteresis
comparator MAX9925/MAX9927
(Notes 5, 6)
20 30 50
VMIN-THRESH - VZERO-THRESH for
MAX9924 (Notes 5, 6) 71526
VMIN-THRESH - VZERO-THRESH for
MAX9926 (Notes 5, 6) 21530
Fixed and Adaptive Peak
Threshold VMIN-THRESH
VMIN-THRESH - VZERO-THRESH for
MAX9925/MAX9927 (Notes 5, 6) 19 30 50
mV
Watchdog Timeout for Adaptive
Peak Threshold tWD
Timing window to reset the adaptive
peak threshold if not triggered (input
level below threshold)
45 85 140 ms
ENTIRE SYSTEM
Comparator Output Low Voltage VCOUT_OL 0.2 V
tPDZ Overdrive = 2V to 3V, zero-crossing 50
Propagation Delay tPDA Overdrive = 2V to 3V, adaptive peak 150 ns
COUT Transition Time tHL-LH 2ns
Propagation Delay Jitter tPD-JITTER
Includes noise of differential amplifier
and comparator, f = 10kHz,
VIN = 1VP-P sine wave
20 ns
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)
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4 _______________________________________________________________________________________
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
EXT
Mode B, TA = +125°C 1.5 VCC
- 1.1
EXT Voltage Range VEXT
Mode C, TA = +125°C 0.14 VCC
- 1.1
V
Input Current to EXT IEXT Mode B, VEXT > VBIAS; and Mode C 10 µA
DIRN (MAX9926 Only)
Output Low Voltage 0.2 V
INT_THRS, ZERO_EN
Low Input VIL 0.3 x
VCC V
High Input VIH 0.7 x
VCC V
Input Leakage ILEAK 1µA
Input Current ZERO_EN ISINK Pullup resistor = 10kΩ,
VZERO_EN = VGND 500 800 µA
Switching Time Between Modes
A1, A2, and Modes B, C tSW
With INT_THRS = GND, auto peak-
detect is disabled, and EXT_THRS is
active
3µs
BIAS
Input Current to BIAS IBIAS Modes A1, A2, B, C 1 µA
Modes A1, B, TA = +125°C 1.5 VCC
- 1.1
BIAS Voltage Range VBIAS
Mode C, TA = +125°C 0.2 VCC
- 1.1
V
Internal BIAS Reference Voltage VINT_BIAS Mode A2 (MAX9924/MAX9926) 2.46 V
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)
Note 2: Specifications are 100% tested at TA= +125°C, unless otherwise noted. All temperature limits are guaranteed by design.
Note 3: Inferred from functional PSRR.
Note 4: CMOS inputs.
Note 5: Guaranteed by design.
Note 6: Includes effect of VOS of internal op amp and comparator.
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
_______________________________________________________________________________________ 5
0
5
10
15
20
INPUT OFFSET VOLTAGE DISTRIBUTION
MAX9924 toc01
INPUT OFFSET VOLTAGE (μV)
PERCENTAGE OF UNITS (%)
-2000
-500
0
-1500
-1000
500
1000
1500
3000
2500
2000
VCM = 0
BIN SIZE = 250
0
0.1
0.3
0.2
0.4
0.5
-0.5 1.50.5 2.5 3.5 4.5 5.5
INPUT OFFSET VOLTAGE
vs. INPUT COMMON-MODE VOLTAGE
MAX9924 toc02
INPUT COMMON-MODE VOLTAGE (V)
INPUT OFFSET VOLTAGE (mV)
VOUT = 2.5V
MAX9925
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
MAX9924 toc03
FREQUENCY (Hz)
CMRR (dB)
10k1k10010
20
40
60
80
100
120
0
1100k
VBIAS = VOUT = 2.5V
VCM = 2VP-P
CMRR = 20log(ADM/ACM)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9924 toc04
FREQUENCY (Hz)
PSSR (dB)
10k1k10010
-100
-80
-60
-40
-20
0
-110
-90
-70
-50
-30
-10
-120
1 100k
VRIPPLE = 100mVP-P
VBIAS = VOUT = 2.5V
INPUTS COUPLED TO GND
OPEN LOOP FREQUENCY
RESPONSE
MAX9924 toc05
FREQUENCY (kHz)
GAIN (dB)
0.1
25
50
75
100
125
0
0.001 10
VCC = 5V
VBIAS = 2.5V
VOUT = 2VP-P
MAX9925
VOL AND VOH vs. TEMPERATURE
MAX9924 toc06
TEMPERATURE (°C)
VOL AND VOH (mV)
50 75 100250-25
15
20
40
5
10
25
30
35
0
-50 125
VCC - VOH
VOL
0
0.2
0.1
0.4
0.3
0.5
0.6
-50 25 50-25 0 75 100 125
INPUT OFFSET VOLTAGE
vs. TEMPERATURE
MAX9924 toc07
TEMPERATURE (°C)
INPUT OFFSET VOLTAGE (mV)
VCM = 0
VOUT = 2.5V
MAX9925
VCM = 2.5V
ADAPTIVE THRESHOLD AND RATIO
vs. SIGNAL LEVEL
MAX9924 toc08
SIGNAL LEVEL (VP)
ADAPTIVE THRESHOLD LEVEL (mV)
1.5 2.01.00.5
400
500
900
100
200
300
600
700
800
0
02.5
fIN = 1kHz
MAX9924
ADAPTIVE THRESHOLD
vs. TEMPERATURE
MAX9924 toc09
TEMPERATURE (°C)
THRESHOLD (mV)
25 50 75 1000-25
200
250
400
50
100
150
300
350
0
-50 125
VIN = 2VP-P
fIN = 1kHz
MAX9924
Typical Operating Characteristics
(VCC = 5V, VGND = 0V, MAX9925/MAX9927 gain setting = 1V/V. All values are at TA= +25°C, unless otherwise noted.)
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VCC = 5V, VGND = 0V, MAX9925/MAX9927 gain setting = 1V/V. All values are at TA= +25°C, unless otherwise noted.)
-5
5
0
15
10
25
20
30
-50 0 25-25 50 75 100 125
MINIMUM AND ZERO-CROSSING
THRESHOLD vs. TEMPERATURE
MAX9924 toc10
TEMPERATURE (°C)
THRESHOLD (mV)
VCM = 2.5V
fIN = 5Hz
ZERO CROSSING
AT 5Hz
MINIMUM THRESHOLD
ZERO CROSSING
AT 1Hz
0
25
50
75
100
CMRR vs. TEMPERATURE
MAX9924 toc11
TEMPERATURE (°C)
CMRR (dB)
-50 25 50-25 0 75 100 125
MAX9924
VCM = 0 TO 5V
INPUT SIGNAL vs. COUT WITH
WATCHDOG TIMER EXPIRED
MAX9924 toc12
20ms/div
VBIAS
5V
fIN = 5Hz
COUT INPUT SIGNAL
INPUT SIGNAL vs. COUT WITH
WATCHDOG TIMER EXPIRED
MAX9924 toc13
100μs/div
VBIAS
5V
fIN = 1kHz
COUT INPUT SIGNAL
833mV
MAX9924 toc14
100μs/div
OVERDRIVEN INPUT VOLTAGES
(MAX9924)
MAX9924 toc15
200μs/div
DIRN OPERATION
(MAX9924)
MAX9924 toc16
INPUT REFERRED NOISE DENSITY
vs. FREQUENCY
10
20
60
40
80
100
10 1k100 10k 100k 1M
FREQUENCY (Hz)
INPUT VOLTAGE NOISE (nV/ Hz)
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
_______________________________________________________________________________________ 7
Pin Description
PIN
MAX9924 MAX9925 MAX9926 MAX9927 NAME FUNCTION
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 Zero-Crossing Enable. Mode configuration pin, internally
pulled up to VCC with 10kΩ resistor.
7 7 — — COUT Comparator Output. Open-drain output, connect a 10kΩ pullup
resistor from COUT to VPULLUP.
8 8 — — EXT External Reference Input. Leave EXT unconnected in Modes
A1, A2. Apply an external voltage in Modes B, C.
9 9 — — INT_THRS Internal Adaptive Threshold. Mode configuration pin.
10 10 14 14 VCC Power Supply
— — 1 1 INT_THRS1 Internal Adaptive Threshold 1. Mode configuration pin.
— — 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 Internal Adaptive Threshold 2. Mode configuration pin.
— — 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 Amplifier Output 1
— — 15 15 IN1- Noninverting Input 1
— — 16 16 IN1+ Inverting Input 1
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
8 _______________________________________________________________________________________
Functional Diagrams
MAX9924
100kΩ
100kΩ
10kΩ
100kΩ
VCC
VCC
MODE
LOGIC
INT_THRS EXT
IN-
100kΩ
VCC
IN+
BIAS
OP AMP
COMPARATOR
30%
BUFFER
INTERNAL
REFERENCE
2.5V
VMIN
THRESHOLD
65ms
WATCHDOG
PEAK
DETECTOR
MODE
LOGIC
COUT
ZERO_EN
INT_THRS
GND
VCC
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
_______________________________________________________________________________________ 9
Functional Diagrams (continued)
MAX9925
10kΩ
VCC
VCC
MODE
LOGIC
EXT
IN- VCC
IN+
BIAS
OP AMP
COMPARATOR
30%
BUFFER
VMIN
THRESHOLD
85ms
WATCHDOG
PEAK
DETECTOR
COUT
ZERO_EN
GND
OUT
VCC
INT_THRS
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
10 ______________________________________________________________________________________
Functional Diagrams (continued)
MAX9926
100kΩ
100kΩ
10kΩ
100kΩ
VCC
VCC
MODE
LOGIC
IN1-
100kΩ
VCC
IN1+
BIAS1
OP AMP
COMPARATOR
30%
BUFFER
INTERNAL
REFERENCE
2.5V
VMIN
THRESHOLD
85ms
WATCHDOG
PEAK
DETECTOR
EXT1
COUT1
ZERO_EN
GND
VCC
100kΩ
100kΩ
100kΩ
VCC
IN2-
100kΩ
VCC
IN2+
BIAS2
OP AMP
COMPARATOR
30%
BUFFER
VMIN
THRESHOLD
85ms
WATCHDOG
PEAK
DETECTOR
EXT2
COUT2
DIRN
DIRN
FLIP-FLOP
CLK
INT_THRS1
INT_THRS2
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
______________________________________________________________________________________ 11
Functional Diagrams (continued)
MAX9927
VCC
IN1- VCC
IN1+
BIAS1
OP AMP
COMPARATOR
30%
BUFFER
VMIN
THRESHOLD
85ms
WATCHDOG
PEAK
DETECTOR
COUT1
EXT1
GND
OUT1
VCC
VCC
IN2- VCC
IN2+
BIAS2
OP AMP
COMPARATOR
30%
BUFFER
VMIN
THRESHOLD
85ms
WATCHDOG
PEAK
DETECTOR
COUT2
OUT1
EXT2
MODE
LOGIC INT_THRS2
INT_THRS1
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
12 ______________________________________________________________________________________
Detailed Description
The MAX9924–MAX9927 interface with variable reluc-
tance (VR) or magnetic coil sensors. These devices
produce accurate pulses aligned with flywheel gear-
teeth even when the pickup signal is small and in the
presence of large amounts of system noise. They inter-
face 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 typical-
ly configured as a differential amplifier by using four
external resistors (the MAX9924/MAX9926 integrate
precision-matched resistors to give superior CMRR per-
formance). 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-
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).
Mode Selection
The MAX9924/MAX9926 provide four modes of opera-
tion: Mode A1, Mode A2, Mode B, and Mode C as deter-
mined 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 zero-
crossing features are enabled. In Mode A2, an internally
generated reference voltage is used to bias the differen-
tial amplifier and all internal circuitry instead of an exter-
nal voltage connected to the BIAS input—this helps
reduce external components and design variables lead-
ing to a more robust application. In Mode B, the adap-
tive 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 imple-
mented 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 ampli-
fier connected to a precision comparator (add external
hysteresis to the comparator for glitch-free operation).
Table 1. MAX9924/MAX9926 Operating Modes
SETTING DEVICE FUNCTIONALITY
OPERATING MODE ZERO_EN INT_THRS ZERO CROSSING ADAPTIVE PEAK
THRESHOLD
BIAS VOLTAGE
SOURCE
A1 VCC VCC Enabled Enabled External
A2 GND GND Enabled Enabled Internal Ref
BV
CC GND Enabled Disabled External
C GND VCC Disabled Disabled External
Table 2. MAX9925 Operating Modes
SETTING DEVICE FUNCTIONALITY
OPERATING MODE ZERO_EN INT_THRS ZERO CROSSING ADAPTIVE PEAK THRESHOLD
A1 VCC VCC Enabled Enabled
BV
CC GND Enabled Disabled
C GND VCC Disabled Disabled
Table 3. MAX9927 Operating Modes
SETTING DEVICE FUNCTIONALITY
OPERATING MODE INT_THRS ZERO CROSSING ADAPTIVE PEAK THRESHOLD
A1 VCC Enabled Enabled
B GND Enabled Disabled
Differential Amplifier
The input operational amplifier is a rail-to-rail input and
output precision amplifier with CMOS input bias cur-
rents, low offset voltage (VOS) and drift. A novel input
architecture eliminates crossover distortion at the oper-
ational 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 precision-
matched 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 perfor-
mance across the entire -40°C to +125°C automotive
temperature range.
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 sta-
ble external BIAS reference.
The minimum threshold, adaptive peak threshold, zero-
crossing threshold signals are all referenced to this
voltage. An input buffer eliminates loading of resistor-
dividers 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 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 volt-
age 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 com-
parator (see the
Zero Crossing
section).
If the input signal voltage remains lower than the adap-
tive 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 intermit-
tent sensor connection.
The internal adaptive peak threshold can be disabled
and directly fed from the EXT input. This mode of opera-
tion is called Mode B, and allows implementations of cus-
tom threshold algorithms in firmware. This EXT voltage is
typically generated by filtering a PWM-modulated output
from an onboard microcontroller (µC). An external opera-
tional amplifier can also be used to construct an active
lowpass filter to filter the PWM-modulated EXT signal.
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
______________________________________________________________________________________ 13
20ms
V1
40ms 60ms
COUT
VR
SIGNAL
ADAPTIVE
THRESHOLD
SET BY V1
ADAPTIVE
THRESHOLD
SET BY V2 MIN
THRESHOLD
80ms 100ms 120ms 140ms 160ms
85ms
V1
1
3V2
1/3 V2
180ms 200ms
Figure 1. Adaptive Peak Threshold Operation
MAX9924–MAX9927
Zero Crossing
The zero-crossing signal provides true timing informa-
tion 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 volt-
age, 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 effec-
tively acts as hysteresis for the comparator, thus pro-
viding 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,
and
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, low-
ering 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 VCC and GND pins. The connection
between these capacitor terminals and the power-sup-
ply pins of the part (both VCC and GND) should be
through wide traces (preferably planes), and without
vias in the high-frequency current path.
VR
RR V
TL BIAS
=+
⎛
⎝
⎜⎞
⎠
⎟×
2
12
VRV V
RR R V
TH PULLUP BIAS
PULLUP BIAS
=−
++
⎛
⎝
⎜
⎞
⎠
⎟+
1
12
()
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
14 ______________________________________________________________________________________
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
______________________________________________________________________________________ 15
Application Circuits
IN+
IN-
BIAS
VCC
ZERO_EN INT_THRS GND
COUT
EXT
TPU
μC
VPULLUP
RPULLUP
1nF
10kΩ
10kΩ
VR
SENSOR
+5V
1kΩ1kΩ
10μF || 0.1μF
MAX9924
MAX9926
Figure 2. MAX9924/MAX9926 Operating Mode A1
IN+
IN-
BIAS
VCC
ZERO_EN INT_THRS GND
COUT
EXT
TPU
μC
VPULLUP
RPULLUP
1nF
10kΩ
10kΩ
VR
SENSOR
+5V
MAX9924
MAX9926
Figure 3. MAX9924/MAX9926 Operating Mode A2
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
16 ______________________________________________________________________________________
Application Circuits (continued)
IN+
IN-
BIAS
VCC
ZERO_EN INT_THRS GND
COUT
EXT
TPU
PWM
μC
VPULLUP
RPULLUP
1nF
10kΩ
10kΩ
VR
SENSOR
+5V
1kΩ1kΩ
10μF || 0.1μF
MAX9924
MAX9926
FILTER
Figure 4. MAX9924/MAX9926 Operating Mode B
IN+
IN-
BIAS
VCC
ZERO_ENINT_THRS
R1
GND
COUT
EXT
TPU
μC
VPULLUP
RPULLUP
R2
1nF
10kΩ
10kΩ
VR
SENSOR
+5V
1kΩ1kΩ
10μF || 0.1μF
MAX9924
MAX9926
Figure 5. MAX9924/MAX9926 Operating Mode C
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
______________________________________________________________________________________ 17
Application Circuits (continued)
IN-
IN+
BIAS
VCC
ZERO_EN INT_THRS GND
COUT
OUT
EXT
TPU
μC
VPULLUP
RPULLUP
1nF
10kΩ
10kΩ
VR
SENSOR
+5V
1kΩ1kΩ
10μF || 0.1μF
MAX9925
MAX9927
Figure 6. MAX9925/MAX9927 Operating Mode A
IN-
IN+
BIAS
VCC
ZERO_EN INT_THRS GND
COUT
OUT
EXT
TPU
μC
VPULLUP
RPULLUP
1nF
10kΩ
10kΩ
VR
SENSOR
+5V
1kΩ1kΩ
10μF || 0.1μF
MAX9925
MAX9927
PWM
FILTER
Figure 7. MAX9925/MAX9927 Operating Mode B
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
18 ______________________________________________________________________________________
Application Circuits (continued)
IN-
IN+
BIAS
VCC
ZERO_ENINT_THRS
R1
GND
COUT
OUT
EXT
TPU
μC
VPULLUP
RPULLUP
R2
+5V
1kΩ1kΩ
10μF || 0.1μF
MAX9925
1nF
10kΩ
10kΩ
VR
SENSOR
Figure 8. MAX9925 Operating Mode C
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
______________________________________________________________________________________ 19
MAX9924
100kΩ
100kΩ
10kΩ
100kΩ
VCC
VCC
4.5V TO 5.5V
VCC
RPULLUP
VPULLUP
MODE
LOGIC
INT_THRS GND
EXT
IN-
100kΩ
VCC
IN+
BIAS
*THE MAX9924 IS
CONFIGURED IN MODE A2.
OP AMP
COMPARATOR
30%
BUFFER
BANDGAP
REFERENCE
VOLTAGE = 2 x VBG
VMIN
THRESHOLD
85ms
WATCHDOG
μC
PEAK
DETECTOR
MODE
LOGIC
COUT TPU
ZERO_EN
VR SENSOR
Typical Operating Circuit
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
20 ______________________________________________________________________________________
Pin Configurations
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
IN_THRS1 IN1+
IN1-
VCC
ZERO_EN
DIRN
GND
IN2-
IN2+
TOP VIEW
MAX9926
QSOP
EXT1
BIAS1
BIAS2
COUT1
COUT2
EXT2
INT_THRS2
+
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
IN_THRS1 IN1+
IN1-
VCC
OUT1
OUT2
GND
IN2-
IN2+
MAX9927
QSOP
EXT1
BIAS1
BIAS2
COUT1
COUT2
EXT2
INT_THRS2
+
1+
2
3
4
5
10
9
8
7
6
VCC
INT_THRS
EXT
COUTBIAS
N.C.
IN-
IN+
MAX9924
μMAX
TOP VIEW
ZERO_ENGND
1
2
3
4
5
10
9
8
7
6
VCC
INT_THRS
EXT
COUTBIAS
OUT
IN-
IN+
MAX9925
μMAX
ZERO_ENGND
+
Chip Information
PROCESS: BiCMOS
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
MAX9924–MAX9927
10LUMAX.EPS
α
α
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
______________________________________________________________________________________ 21
PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
10 µMAX U10+2 21-0061 90-0330
16 QSOP E16+1 21-0055 90-0167
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 per-
tains to the package regardless of RoHS status.
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
22 ______________________________________________________________________________________
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 per-
tains to the package regardless of RoHS status.
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
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
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Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 10/08 Initial release —
1 2/09 Removed future product references for the MAX9926 and MAX9927, updated EC
table 1–4
2 3/09 Corrected various errors
3/11 Updated Figures 6, 7, and 8
3/12 Added automotive qualifies parts
2, 3, 4, 6, 13
3 17, 18
4 1
