MAX9924-27 Datasheet by Maxim Integrated

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19-4283; Rev 5; 8/18
General Description
The MAX9924–MAX9927 variable reluctance (VR or
magnetic coil) sensor interface devices are ideal for posi-
tion and speed sensing for automotive crankshafts, cam-
shafts, transmission shafts, etc. These devices integrate a
precision amplifier and comparator with selectable adap-
tive 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 quadrature-
connected 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 avail-
able in the 16-pin QSOP package. All devices are specified
over the -40°C to +125°C automotive temperature range.
Features
Differential Input Stage Provides Enhanced Noise
Immunity
Precision Amplifier and Comparator Allows
Small-Signal Detection
User-Enabled Internal Adaptive Peak Threshold or
Flexible External Threshold
Zero-Crossing Detection Provides Accurate
Phase Information
Applications
Camshaft VRS Interfaces
Crankshaft VRS Interfaces
Vehicle Speed VRS Interfaces
μMAX is a registered trademark of Maxim Integrated Products, Inc.
+Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
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
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
Simplified Block Diagram
Ordering Information
Click here for production status of specific part numbers.
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
(Note 1)
μMAX
Junction-to-Ambient Thermal Resistance JA) .....113.1°C/W
Junction-to-Case Thermal Resistance JC) ...............42°C/W
QSOP
Junction-to-Ambient Thermal Resistance JA) .....103.7°C/W
Junction-to-Case Thermal Resistance JC) ...............37°C/W
(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 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
http://www.maximintegrated.com/thermal-tutorial
.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
POWER SUPPLY
Operating Supply Range VCC (Note 3) 4.5 5.5 V
Supply Current ICC
MAX9924/MAX9925 2.6 5 mA
MAX9926/MAX9927 4.7 10
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
Input Offset Voltage VOS-OA
Temperature drift 5 µV/°C
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
Power-Supply Rejection Ratio PSRR MAX9925 88 105 dB
MAX9927 77 94
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
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MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Absolute Maximum Ratings
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
Package Thermal 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 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
Differential Amplifier
Common-Mode Rejection Ratio CMRR MAX9924 (Note 5) 60 87 dB
MAX9926 (Note 5) 55 78
Input Resistance RIN (Note 5) 65 100 135 kΩ
ADAPTIVE PEAK DETECTION
Zero-Crossing Threshold VZERO_THRESH
Mode B
operation
(Notes 5, 6)
MAX9924/MAX9925 -6.5 0 +6.5
mV
MAX9926/MAX9927 -6.5 0 +10
Fixed and Adaptive Peak
Threshold
VADAPTIVE Adaptive peak threshold 33 %PK
VMIN-THRESH
Minimum threshold of hysteresis
comparator MAX9924/MAX9926
(Notes 5, 6)
4 15 30
mV
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
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
Propagation Delay
tPDZ Overdrive = 2V to 3V, zero-crossing
path 50
ns
tPDA Overdrive = 2V to 3V, adaptive peak
path 150
COUT Transition Time tHL-LH 2 ns
Propagation Delay Jitter tPD-JITTER
Includes noise of differential amplifier
and comparator, f = 10kHz,
VIN = 1VP-P sine wave
20 ns
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MAX9924–MAX9927 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)
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.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
EXT
EXT Voltage Range VEXT
Mode B, TA = +125°C 1.5 VCC
- 1.1 V
Mode C, TA = +125°C 0.14 VCC
- 1.1
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 1 µA
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
3 µs
BIAS
Input Current to BIAS IBIAS Modes A1, A2, B, C 1 µA
BIAS Voltage Range VBIAS
Modes A1, B, TA = +125°C 1.5 VCC
- 1.1
V
Mode C, TA = +125°C 0.2 VCC
- 1.1
Internal BIAS Reference Voltage VINT_BIAS Mode A2 (MAX9924/MAX9926) 2.46 V
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MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Electrical Characteristics (continued)
INPUT OFFSET VOLTAGE COMMON-MODE REJECTION RATIO //
(VCC = 5V, VGND = 0V, MAX9925/MAX9927 gain setting = 1V/V. All values are at TA = +25°C, unless otherwise noted.)
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
1 100k
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)
V
OL
AND V
OH
(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
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
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
0 2.5
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
Maxim Integrated
5
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MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Typical Operating Characteristics
WITH RED cum
(VCC = 5V, VGND = 0V, MAX9925/MAX9927 gain setting = 1V/V. All values are at TA = +25°C, unless otherwise noted.)
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)
-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)
VCM = 2.5V
fIN = 5Hz
ZERO CROSSING
AT 5Hz
MINIMUM THRESHOLD
ZERO CROSSING
AT 1Hz
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)
Maxim Integrated
6
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MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Typical Operating Characteristics (continued)
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 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
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MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Pin Description
MAX9924
100k
100k
10k
100k
VCC
VCC
MODE
LOGIC
INT_THRS EXT
IN-
100k
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
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MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Functional Diagrams
MAX9925
10k
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
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MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Functional Diagrams (continued)
MAX9926
100k
100k
10k
100k
VCC
VCC
MODE
LOGIC
IN1-
100k
VCC
IN1+
BIAS1
OP AMP
COMPARATOR
30%
BUFFER
INTERNAL
REFERENCE
2.5V
VMIN
THRESHOLD
85ms
WATCHDOG
PEAK
DETECTOR
EXT1
COUT1
ZERO_EN
GND
VCC
100k
100k
100k
VCC
IN2-
100k
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
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MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
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
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MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Functional Diagrams (continued)
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 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, respec-
tively. 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 com-
parator 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 opera-
tion: 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 zero-
crossing 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 func-
tionality 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 com-
parator for glitch-free operation).
Table 1. MAX9924/MAX9926 Operating Modes
Table 2. MAX9925 Operating Modes
Table 3. MAX9927 Operating Modes
OPERATING
MODE
SETTING DEVICE FUNCTIONALITY
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
B VCC GND Enabled Disabled External
C GND VCC Disabled Disabled External
OPERATING MODE SETTING DEVICE FUNCTIONALITY
ZERO_EN INT_THRS ZERO CROSSING ADAPTIVE PEAK THRESHOLD
A1 VCC VCC Enabled Enabled
B VCC GND Enabled Disabled
C GND VCC Disabled Disabled
OPERATING MODE SETTING DEVICE FUNCTIONALITY
INT_THRS ZERO CROSSING ADAPTIVE PEAK THRESHOLD
A1 VCC Enabled Enabled
B GND Enabled Disabled
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MAX9924–MAX9927 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 archi-
tecture eliminates crossover distortion at the operational
amplifier inputs normally found in rail-to-rail input struc-
tures. These features enable reliable small-signal detec-
tion 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 resis-
tors 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.
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, zero-
crossing threshold signals are all referenced to this volt-
age. 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 voltage
scheme provides robust noise immunity to the input VR
signal, preventing false triggers from occurring due to bro-
ken 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 arm-
ing 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 recogni-
tion 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 typi-
cally 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.
Figure 1. Adaptive Peak Threshold Operation
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
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13
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 dif-
ferential amplifier is level-shifted to the BIAS voltage, the
zero of the input VR signal is simply BIAS. The compara-
tor 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 dif-
ference in these two voltages then effectively acts as hys-
teresis 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:
PULLUP BIAS
TH BIAS
PULLUP
R1( V V )
VV
R1 R2 R

= +

++

and
TL BIAS
R2
VV
R1 R2

= ×

+

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 cir-
cuits. 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-res-
onance 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 VCC and
GND pins. The connection between these capacitor termi-
nals 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.
Input Filter Considerations
Add a series 10kΩ resistor to each input of the operational
amplifier of the MAX9924/MAX9926 to limit the pin cur-
rents in case the internal ESD diodes are turned on. This
can happen when the sensor pulse voltage is higher than
the VCC voltage. The series resistors lower the gain of
the input amplifier and should be accounted for when set-
ting the trigger threshold. Add a filter capacitor between
the operational amplifier inputs to limit the input signal
bandwidth.
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14
MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
WW ’VV\/—' ‘H’ Wm
Figure 2. MAX9924/MAX9926 Operating Mode A1
Figure 3. MAX9924/MAX9926 Operating Mode A2
IN+
IN-
BIAS
VCC
ZERO_EN INT_THRS GND
COUT
EXT
TPU
µC
VPULLUP
RPULLUP
1nF
10k
10k
VR
SENSOR
+5V
1k1k
10µF || 0.1µF
MAX9924
MAX9926
IN+
IN-
BIAS
VCC
ZERO_EN INT_THRS GND
COUT
EXT
TPU
µC
VPULLUP
RPULLUP
1nF
10k
10k
VR
SENSOR
+5V
MAX9924
MAX9926
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15
MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Application Circuits
L % TPU mm PWM TPU
Figure 4. MAX9924/MAX9926 Operating Mode B
Figure 5. MAX9924/MAX9926 Operating Mode C
IN+
IN-
BIAS
VCC
ZERO_EN INT_THRS GND
COUT
EXT
TPU
PWM
µC
VPULLUP
RPULLUP
1nF
10k
10k
VR
SENSOR
+5V
1k1k
10µF || 0.1µF
MAX9924
MAX9926
FILTER
IN+
IN-
BIAS
VCC
ZERO_ENINT_THRS
R1
GND
COUT
EXT
TPU
µC
VPULLUP
RPULLUP
R2
1nF
10k
10k
VR
SENSOR
+5V
1k1k
10µF || 0.1µF
MAX9924
MAX9926
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16
MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Application Circuits (continued)
% my
Figure 6. MAX9925/MAX9927 Operating Mode A
Figure 7. MAX9925/MAX9927 Operating Mode B
IN-
IN+
BIAS
VCC
ZERO_EN INT_THRS GND
COUT
OUT
EXT
TPU
µC
VPULLUP
RPULLUP
1nF
10k
10k
VR
SENSOR
+5V
1k1k
10µF || 0.1µF
MAX9925
MAX9927
IN-
IN+
BIAS
VCC
ZERO_EN INT_THRS GND
COUT
OUT
EXT
TPU
µC
VPULLUP
RPULLUP
1nF
10k
10k
VR
SENSOR
+5V
1k1k
10µF || 0.1µF
MAX9925
MAX9927 PWM
FILTER
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17
MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Application Circuits (continued)
mm TF‘U
Figure 8. MAX9925 Operating Mode C
IN-
IN+
BIAS
VCC
ZERO_ENINT_THRS
R1
GND
COUT
OUT
EXT
TPU
µC
VPULLUP
RPULLUP
R2
+5V
1k1k
10µF || 0.1µF
MAX9925
1nF
10k
10k
VR
SENSOR
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18
MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Application Circuits (continued)
l Wm H ,, DZ}? w A
MAX9924
100k
100k
10k
100k
VCC
VCC
4.5V TO 5.5V
VCC
RPULLUP
VPULLUP
MODE
LOGIC
INT_THRS GND
EXT
IN-
100k
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
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19
MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Typical Operating Circuit
_|:J_J_I:I:I:I:J 131]: CCCCCCCC CCCCC 3333333] 131]: CCCCCCCC CCCCC
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
1+
2
3
4
5
10
9
8
7
6
VCC
INT_THRS
EXT
COUTBIAS
N.C.
IN-
IN+
MAX9924
µMAX
ZERO_ENGND
1
2
3
4
5
10
9
8
7
6
VCC
INT_THRS
EXT
COUTBIAS
OUT
IN-
IN+
MAX9925
µMAX
ZERO_ENGND
+
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
+
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20
MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Pin Configurations
Selector Guide Chip Information
PROCESS: BiCMOS
Hum“ TOP V‘EW D2 *4 0 7M4: V A”? 44 m FRONT V‘EW NDTES rmnch 03E nu NEIT INCLUEE MEILD FLASH MEILD FLASH EIR PRJTRUXIDNS um TEI EXCEED 015mm (006') CEINTREILLING mMEnsmw MILLIMETERS EOT'ON V‘EW ‘0 \NCHES M‘LUMETERS 0w MW MAX MW MAX A 7 o 043 r w 40 m 0002 0005 005 045 A2 0 030 0 037 0 75 0 95 m 0H6 0120 295 305 02 0444 0445 259 300 E4 0 MG 0 420 2,95 305 E2 004 000 259 300 H 0457 0499 475 505 L 0.0457 0.0275 040 070 U 0037 REF 04940 REF 5 0007 [00105 0477‘ 0270 ‘ e 0 0497 ESC 0 500 050 c 0 0055 l 0 0075 0 090‘ 0.200 5 0,0490 REF 0495 REF (1 0' \ 6‘ 0' \ 0' Pkg Cones 07072, 04007474 Rag 0403 PLANE %— I a x We J L p A u ( S‘DE V‘EW MARKING SHDVN IS FDR PKG CPIENTATIUV DNLY 1 a 3 4 COMPUES 70 JEDEC M07187, LATEST REV‘S‘ON, VARWON EA 5 5‘ ALL DIMENsmN: APPLY TEI EU'H LEADED <7) and="" f'kzfpee="" m="" pm="" ceides="" rdraw‘ng="" not="" 70="" scaler="" mam.="" men-axed.="" nu;="" package="" ou‘une,="" 40l="" umax/usop="" ”mom="" docwewcmwmnn="" wzv="" ‘/="" 2170061="" l="">
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
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21
MAX9924–MAX9927 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.maximintegrated.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.
INCHES MILLIMETERS A m MIN MAX MIN MAX MAQKING A 053 as? 135 175 A1 mm mu ‘mz 554 A? m Lass L245 Les; 7 h x 46‘“ ‘k a one ma uzu nan : M75 Loose am 0245 [fl D ‘SEE VARIATIDN‘S E 150 157 (LEI 355 H E { J k f5 a Dean: mm: H an 244 554 sen \ H‘ , L a L Us ms an as; ' L4» ‘7 N 5:: vmmuNs u n~ \s‘ \n' \y W Tm: vxw VARIATIEINX‘ mm: MILLIMETERS 4. ‘72 B4 .7 MIN MAX MIN MAX N PKC cunEs 7A2 u 189 we «an «95 16 EA571,EA5H*I,EA574,[1673, \ H S ‘DUEU £070 0‘05 UJE as,” A1 D 337 SM 855 B74 EC E2071. Eznr , [Eur] L L aim F : Lusun ‘0550 Law 1397 , , , n 13/ m was an zazzm. [241,901 r \Q‘uwmm‘ : D u see. 393 m sea 23 E92171, spam, m4 : 025D ma uses me 51mm NEITESL L n l E DEI NIIIT INCLUDE MEILD FLASH EIR PRmRusmNs e MEILD FLASH EIR PREITRuSIENS NEIT m EXCEED nus- PER SIDE 3‘ CDNTREILLING DIMENSIEINS‘ INCHES . MEET: JEDEC Nn137L "‘fx‘m‘ d MARKING SHEIWN [S FDR PK; DRIENTATIEIN EINLV‘ "‘ ’3'“ ' E1 ALL DIMENSIDNS APPLY TEI BETH LEADED (,) AND PbFREE (+) PKG EDDES “WE PACKAGE EIUTLINE DEEP 150‘, 025' LEAD PITCH rDRAW‘NC NOT TO SCALEi mom Docwim CONWOL No m 2141355 J
www.maximintegrated.com Maxim Integrated
22
MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Package Information (continued)
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.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.
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
010/08 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 2, 3, 4, 6, 13
3 3/11 Updated Figures 6, 7, and 8 17, 18
4 3/12 Added automotive qualifies parts 1
56/18 Added Input Filter Considerations section 14
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2018 Maxim Integrated Products, Inc.
23
MAX9924–MAX9927 Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Revision History
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.

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