MAX9924_V01 [MAXIM]
Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold;
| 型号： | MAX9924_V01 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold |
| 文件： | 总23页 (文件大小：1276K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
General Description
Features
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.
● 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
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.
Applications
● Camshaft VRS Interfaces
● Crankshaft VRS Interfaces
● Vehicle Speed VRS Interfaces
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX9924UAUB+
MAX9924UAUB/V+
MAX9925AUB+
MAX9926UAEE+
MAX9926UAEE/V+
MAX9927AEE+
MAX9927AEE/V+
-40°C to +125°C 10 µMAX
-40°C to +125°C 10 µMAX
-40°C to +125°C 10 µMAX
-40°C to +125°C 16 QSOP
-40°C to +125°C 16 QSOP
-40°C to +125°C 16 QSOP
-40°C to +125°C 16 QSOP
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.
+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
ENGINE BLOCK
MAX9924
DIFFERENTIAL
AMPLIFIER
VR SENSOR
µC
ADAPTIVE/MINIMUM
AND
ZERO-CROSSING
THRESHOLDS
INTERNAL/EXTERNAL
BIAS VOLTAGE
19-4283; Rev 5; 8/18
MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Absolute Maximum Ratings
CC
All Other Pins ........................................... -0.3V to (V
Current into IN+, IN-, IN_+, IN_- ......................................±40mA
Current into All Other Pins................................................±20mA
Output Short-Circuit (OUT_, OUT) to GND........................... 10s
V
to GND ...........................................................-0.3V to + 6V
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
+ 0.3V)
CC
Continuous Power Dissipation (T = +70°C) (Note 1)
A
10-Pin μMAX (derate 8.8mW/°C above +70°C).......707.3mW
16-Pin QSOP (derate 9.6mW/°C above +70°C).......771.5mW
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.
(Note 1)
Package Thermal Characteristics
μMAX
QSOP
Junction-to-Ambient Thermal Resistance (θ ) .....103.7°C/W
Junction-to-Ambient Thermal Resistance (θ ) .....113.1°C/W
JA
JA
Junction-to-Case Thermal Resistance (θ )...............42°C/W
Junction-to-Case Thermal Resistance (θ )...............37°C/W
JC
JC
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
.
Electrical Characteristics
(V
= 5V, V
= 0V, MAX9925/MAX9927 gain setting = 1V/V, Mode A1, V
= 2.5V, V
= 5V, R
= 1kΩ, C
=
COUT
CC
GND
BIAS
PULLUP
PULLUP
50pF. T = T
to T
, unless otherwise noted. Typical values are at T = +25°C.) (Note 2)
MAX A
A
MIN
PARAMETER
POWER SUPPLY
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Operating Supply Range
V
(Note 3)
4.5
5.5
5
V
CC
MAX9924/MAX9925
MAX9926/MAX9927
2.6
4.7
Supply Current
I
mA
CC
10
V
V
> V
~ 1µs
= 4.1V, step time for
CC
CC
UVLO
Power-On Time
P
30
150
µs
ON
INPUT OPERATIONAL AMPLIFIER (MAX9925/MAX9927)
Input Voltage Range
IN+, IN-
Guaranteed by CMRR
Temperature drift
0
V
V
µV/°C
mV
nA
CC
5
Input Offset Voltage
V
OS-OA
0.5
0.1
3
6
2
Input Bias Current
I
(Note 4)
(Note 4)
BIAS
Input Offset Current
I
0.05
102
105
94
nA
OFFSET
CMRR
Common-Mode Rejection Ratio
From V
= 0 to V
75
88
77
dB
CM
CC
MAX9925
MAX9927
Power-Supply Rejection Ratio
Output Voltage Low
PSRR
dB
V
V
I
= 1mA
0.050
OL
OL
V
CC
Output Voltage High
V
I
= -1mA
V
OH
OH
-0.050
To 1% of the actual V
saturates
after output
OUT
Recovery Time from Saturation
t
1.2
µs
SAT
Gain-Bandwidth Product
Slew Rate
GBW
1.4
2.3
1.3
MHz
V/µs
MHz
SR
Charge-Pump Frequency
f
CP
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Electrical Characteristics (continued)
(V
= 5V, V
= 0V, MAX9925/MAX9927 gain setting = 1V/V, Mode A1, V
= 2.5V, V
= 5V, R
= 1kΩ, C
=
COUT
CC
GND
BIAS
PULLUP
PULLUP
50pF. T = T
to T
, unless otherwise noted. Typical values are at T = +25°C.) (Note 2)
MAX A
A
MIN
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
INPUT DIFFERENTIAL AMPLIFIER (MAX9924/MAX9926)
V
+
CC
0.3
Input Voltage Range
IN+, IN-
CMRR
Guaranteed by CMRR
-0.3
V
MAX9924 (Note 5)
MAX9926 (Note 5)
(Note 5)
60
55
65
87
78
Differential Amplifier
Common-Mode Rejection Ratio
dB
Input Resistance
R
100
135
kΩ
IN
ADAPTIVE PEAK DETECTION
Mode B
operation
(Notes 5, 6)
MAX9924/MAX9925
MAX9926/MAX9927
-6.5
-6.5
0
+6.5
+10
Zero-Crossing Threshold
V
mV
ZERO_THRESH
0
V
Adaptive peak threshold
33
%PK
ADAPTIVE
Minimum threshold of hysteresis
comparator MAX9924/MAX9926
(Notes 5, 6)
4
15
30
30
50
Minimum threshold of hysteresis
comparator MAX9925/MAX9927
(Notes 5, 6)
20
Fixed and Adaptive Peak
Threshold
V
mV
MIN-THRESH
V
- V
for
for
for
MIN-THRESH
ZERO-THRESH
7
2
15
15
30
26
30
50
MAX9924 (Notes 5, 6)
V
- V
MIN-THRESH
ZERO-THRESH
MAX9926 (Notes 5, 6)
V
- V
MIN-THRESH
ZERO-THRESH
19
MAX9925/MAX9927 (Notes 5, 6)
Timing window to reset the adaptive
peak threshold if not triggered (input
level below threshold)
Watchdog Timeout for Adaptive
Peak Threshold
t
45
85
140
0.2
ms
WD
ENTIRE SYSTEM
Comparator Output Low Voltage
V
V
COUT_OL
Overdrive = 2V to 3V, zero-crossing
path
t
50
PDZ
PDA
Propagation Delay
ns
Overdrive = 2V to 3V, adaptive peak
path
t
150
2
COUT Transition Time
Propagation Delay Jitter
t
ns
ns
HL-LH
Includes noise of differential amplifier
and comparator, f = 10kHz,
t
20
PD-JITTER
V
= 1V
sine wave
IN
P-P
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Electrical Characteristics (continued)
(V
= 5V, V
= 0V, MAX9925/MAX9927 gain setting = 1V/V, Mode A1, V
= 2.5V, V
= 5V, R
= 1kΩ, C
=
COUT
CC
GND
BIAS
PULLUP
PULLUP
50pF. T = T
to T
, unless otherwise noted. Typical values are at T = +25°C.) (Note 2)
MAX A
A
MIN
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
EXT
V
- 1.1
CC
Mode B, T = +125°C
1.5
A
EXT Voltage Range
V
V
EXT
V
- 1.1
CC
Mode C, T = +125°C
0.14
A
Input Current to EXT
DIRN (MAX9926 Only)
Output Low Voltage
INT_THRS, ZERO_EN
I
Mode B, V
> V
; and Mode C
10
µA
V
EXT
EXT
BIAS
0.2
0.3 x
Low Input
V
V
IL
V
CC
0.7 x
High Input
V
V
IH
V
CC
Input Leakage
I
1
µA
µA
LEAK
Pullup resistor = 10kΩ,
= V
Input Current ZERO_EN
I
500
3
800
SINK
V
ZERO_EN
GND
With INT_THRS = GND, auto peak-
detect is disabled, and EXT_THRS is
active
Switching Time Between Modes
A1, A2, and Modes B, C
t
µs
SW
BIAS
Input Current to BIAS
I
Modes A1, A2, B, C
1
µA
V
BIAS
V
CC
- 1.1
Modes A1, B, T = +125°C
1.5
0.2
A
BIAS Voltage Range
V
BIAS
V
CC
- 1.1
Mode C, T = +125°C
A
Internal BIAS Reference Voltage
V
Mode A2 (MAX9924/MAX9926)
2.46
V
INT_BIAS
Note 2: Specifications are 100% tested at T = +125°C, unless otherwise noted. All temperature limits are guaranteed by design.
A
Note 3: Inferred from functional PSRR.
Note 4: CMOS inputs.
Note 5: Guaranteed by design.
Note 6: Includes effect of V
of internal op amp and comparator.
OS
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Typical Operating Characteristics
(V
= 5V, V
= 0V, MAX9925/MAX9927 gain setting = 1V/V. All values are at T = +25°C, unless otherwise noted.)
CC
GND A
INPUT OFFSET VOLTAGE
vs. INPUT COMMON-MODE VOLTAGE
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
INPUT OFFSET VOLTAGE DISTRIBUTION
120
100
80
60
40
20
0
20
0.5
0.4
0.3
0.2
0.1
0
V
= 0
CM
BIN SIZE = 250
15
10
5
V
V
= V
= 2.5V
BIAS
OUT
V
= 2.5V
= 2V
OUT
CM
P-P
MAX9925
CMRR = 20log(A /A
)
DM CM
0
0
2000
2500
-2000 -1000
1000
1500
INPUT OFFSET VOLTAGE (µV)
3000
-0.5
0.5
1.5
2.5
3.5
4.5
5.5
1
10
100
1k
10k
100k
-500
500
-1500
INPUT COMMON-MODE VOLTAGE (V)
FREQUENCY (Hz)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
OPEN LOOP FREQUENCY
RESPONSE
V
OL
AND V vs. TEMPERATURE
OH
0
-10
125
100
75
50
25
0
40
35
V
V
= 100mV
V
V
V
= 5V
RIPPLE
P-P
CC
= V
= 2.5V
= 2.5V
BIAS
OUT
BIAS
OUT
-20
INPUTS COUPLED TO GND
= 2V
P-P
-30
30
25
MAX9925
-40
-50
V
CC
- V
OH
-60
20
15
10
5
-70
V
OL
-80
-90
-100
-110
-120
0
1
10
100
1k
10k
100k
0.001
0.1
FREQUENCY (kHz)
10
-50 -25
0
25
50
75 100 125
FREQUENCY (Hz)
TEMPERATURE (°C)
ADAPTIVE THRESHOLD AND RATIO
vs. SIGNAL LEVEL
INPUT OFFSET VOLTAGE
vs. TEMPERATURE
ADAPTIVE THRESHOLD
vs. TEMPERATURE
900
800
700
600
500
400
300
200
100
0
400
350
0.6
0.5
0.4
0.3
0.2
0.1
0
V
= 2.5V
OUT
MAX9925
300
250
V
= 0
CM
200
150
100
V
CM
= 2.5V
V
f
= 2V
P-P
= 1kHz
IN
IN
f
= 1kHz
IN
50
0
MAX9924
MAX9924
0
0.5
1.0
1.5
2.0
2.5
-50 -25
0
25
50
75 100 125
-50 -25
0
25
50
75 100 125
SIGNAL LEVEL (V )
TEMPERATURE (°C)
TEMPERATURE (°C)
P
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Typical Operating Characteristics (continued)
(V
= 5V, V
= 0V, MAX9925/MAX9927 gain setting = 1V/V. All values are at T = +25°C, unless otherwise noted.)
CC
GND A
INPUT SIGNAL vs. COUT WITH
WATCHDOG TIMER EXPIRED
MINIMUM AND ZERO-CROSSING
THRESHOLD vs. TEMPERATURE
CMRR vs. TEMPERATURE
MAX9924 toc12
100
75
50
25
0
30
COUT
V
= 2.5V
= 5Hz
CM
INPUT SIGNAL
MINIMUM THRESHOLD
f
IN
25
20
15
10
5
5V
V
BIAS
ZERO CROSSING
AT 5Hz
ZERO CROSSING
AT 1Hz
MAX9924
0
V
CM
= 0 TO 5V
f
= 5Hz
IN
-5
-50 -25
0
25
50
75 100 125
20ms/div
-50 -25
0
25
50
75 100 125
TEMPERATURE (°C)
TEMPERATURE (°C)
OVERDRIVEN INPUT VOLTAGES
(MAX9924)
INPUT SIGNAL vs. COUT WITH
WATCHDOG TIMER EXPIRED
MAX9924 toc13
MAX9924 toc14
COUT
INPUT SIGNAL
5V
833mV
V
BIAS
f
= 1kHz
IN
100µs/div
100µs/div
DIRN OPERATION
(MAX9924)
INPUT REFERRED NOISE DENSITY
vs. FREQUENCY
MAX9924 toc15
MAX9924 toc16
100
80
60
40
20
10
200µs/div
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Pin Description
PIN
NAME
FUNCTION
MAX9924 MAX9925 MAX9926 MAX9927
1
2
1
2
—
—
—
—
—
—
—
—
IN+
IN-
Noninverting Input
Inverting Input
—
3
3
OUT
N.C.
Amplifier Output
—
No Connection. Not internally connected.
Input Bias. Connect to an external resistor-divider and bypass
to ground with a 0.1µF and 10µF capacitor.
4
5
6
4
5
6
—
11
13
—
11
—
BIAS
GND
Ground
Zero-Crossing Enable. Mode configuration pin, internally
ZERO_EN
pulled up to V
with 10kΩ resistor.
CC
Comparator Output. Open-drain output, connect a 10kΩ
pullup resistor from COUT to V
7
7
—
—
—
—
COUT
.
PULLUP
External Reference Input. Leave EXT unconnected in Modes
A1, A2. Apply an external voltage in Modes B, C.
8
8
EXT
9
9
—
14
1
—
14
1
INT_THRS
Internal Adaptive Threshold. Mode configuration pin.
10
—
10
—
V
Power Supply
CC
INT_THRS1 Internal Adaptive Threshold 1. Mode configuration pin.
External Reference Input 1. Leave EXT unconnected in
EXT1
—
—
—
—
—
—
—
—
—
—
—
—
2
3
4
5
6
7
2
3
4
5
6
7
Modes A1, A2. Apply an external voltage in Modes B, C.
Input Bias 1. Connect to an external resistor-divider and
BIAS1
bypass to ground with a 0.1µF and 10µF capacitor.
Comparator Output 1. Open-drain output, connect a 10kΩ
COUT1
pullup resistor from COUT1 to V
.
PULLUP
Comparator Output 2. Open-drain output, connect a 10kΩ
pullup resistor from COUT2 to V
COUT2
BIAS2
EXT2
.
PULLUP
Input Bias 2. Connect to an external resistor-divider and
bypass to ground with a 0.1µF and 10µF capacitor.
External Reference Input 2. Leave EXT unconnected in
Modes A1, A2. Apply an external voltage in Modes B, C.
—
—
—
—
—
—
8
9
8
9
INT_THRS2 Internal Adaptive Threshold 2. Mode configuration pin.
IN2+
IN2-
Noninverting Input 2
10
10
Inverting Input 2
Rotational Direction Output. Open-drain output, connect a
—
—
12
—
DIRN
pullup resistor from DIRN to V
.
PULLUP
—
—
—
—
—
—
—
—
—
—
15
16
12
13
15
16
OUT2
OUT1
IN1-
Amplifier Output 2
Amplifier Output 1
Noninverting Input 1
Inverting Input 1
IN1+
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Functional Diagrams
100kΩ
V
CC
V
CC
100kΩ
100kΩ
IN-
V
CC
MAX9924
OP AMP
GND
IN+
100kΩ
65ms
WATCHDOG
COMPARATOR
COUT
INTERNAL
REFERENCE
2.5V
BUFFER
30%
V
CC
BIAS
PEAK
DETECTOR
10kΩ
MODE
LOGIC
V
MIN
ZERO_EN
INT_THRS
THRESHOLD
MODE
LOGIC
INT_THRS
EXT
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Functional Diagrams (continued)
OUT
V
CC
V
CC
MAX9925
IN-
V
CC
OP AMP
GND
IN+
85ms
WATCHDOG
COMPARATOR
COUT
BIAS
BUFFER
30%
V
CC
PEAK
DETECTOR
10kΩ
V
MIN
MODE
LOGIC
ZERO_EN
INT_THRS
THRESHOLD
EXT
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Functional Diagrams (continued)
100kΩ
V
CC
V
CC
100kΩ
100kΩ
MAX9926
IN1-
V
CC
OP AMP
GND
IN1+
100kΩ
85ms
WATCHDOG
COMPARATOR
COUT1
INTERNAL
REFERENCE
2.5V
BUFFER
30%
BIAS1
PEAK
DETECTOR
CLK
V
MIN
DIRN
DIRN
FLIP-FLOP
THRESHOLD
EXT1
100kΩ
V
CC
100kΩ
IN2-
V
CC
OP AMP
100kΩ
IN2+
100kΩ
85ms
WATCHDOG
COMPARATOR
COUT2
BUFFER
30%
V
CC
BIAS2
PEAK
DETECTOR
10kΩ
V
MIN
ZERO_EN
MODE
LOGIC
THRESHOLD
INT_THRS1
INT_THRS2
EXT2
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Functional Diagrams (continued)
OUT1
V
CC
V
CC
MAX9927
IN1-
V
CC
OP AMP
GND
IN1+
85ms
WATCHDOG
COMPARATOR
COUT1
BIAS1
BUFFER
30%
PEAK
DETECTOR
V
MIN
THRESHOLD
EXT1
V
CC
IN2-
V
CC
OP AMP
OUT1
IN2+
85ms
WATCHDOG
COMPARATOR
COUT2
BIAS2
BUFFER
30%
INT_THRS1
INT_THRS2
MODE
LOGIC
PEAK
DETECTOR
V
MIN
THRESHOLD
EXT2
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
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).
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.
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).
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
Table 1. MAX9924/MAX9926 Operating Modes
SETTING
DEVICE FUNCTIONALITY
OPERATING
ADAPTIVE PEAK
THRESHOLD
BIAS VOLTAGE
MODE
ZERO_EN
INT_THRS
ZERO CROSSING
SOURCE
A1
A2
B
V
V
Enabled
Enabled
Enabled
Disabled
Enabled
Enabled
Disabled
Disabled
External
Internal Ref
External
CC
CC
GND
GND
GND
V
CC
C
GND
V
External
CC
Table 2. MAX9925 Operating Modes
SETTING
DEVICE FUNCTIONALITY
OPERATING MODE
ZERO_EN
INT_THRS
ZERO CROSSING
ADAPTIVE PEAK THRESHOLD
A1
B
V
V
V
Enabled
Enabled
Disabled
Enabled
Disabled
Disabled
CC
CC
GND
CC
C
GND
V
CC
Table 3. MAX9927 Operating Modes
SETTING
OPERATING MODE
DEVICE FUNCTIONALITY
INT_THRS
ZERO CROSSING
Enabled
ADAPTIVE PEAK THRESHOLD
A1
B
V
Enabled
Disabled
CC
GND
Enabled
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Differential Amplifier
Adaptive Peak Threshold
The input operational amplifier is a rail-to-rail input and
output precision amplifier with CMOS input bias currents,
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.
low offset voltage (V ) and drift. A novel input archi-
OS
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 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).
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 V /2 signal for the BIAS
CC
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.
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 (V
). This ensures pulse recogni-
MIN_THRESH
tion recovers even in the presence of intermittent sensor
connection.
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.
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.
ADAPTIVE
THRESHOLD
SET BY V2
ADAPTIVE
THRESHOLD
SET BY V1
MIN
THRESHOLD
1
3
V2
V1
VR
SIGNAL
V1
1/3 V2
85ms
COUT
20ms
40ms
60ms
80ms
100ms
120ms
140ms
160ms
180ms
200ms
Figure 1. Adaptive Peak Threshold Operation
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Zero Crossing
Applications Information
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.
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.
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.
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
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:
1μF, with the 10nF placed closest between the V
and
CC
GND pins. The connection between these capacitor termi-
nals and the power-supply pins of the part (both V and
CC
GND) should be through wide traces (preferably planes),
and without vias in the high-frequency current path.
R1( V
− V
)
PULLUP
BIAS
V
=
+ V
BIAS
Input Filter Considerations
TH
R1+ R2 + R
PULLUP
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
and
R2
V
=
× V
the V
voltage. The series resistors lower the gain of
TL
BIAS
CC
R1+ R2
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.
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.
Maxim Integrated
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Application Circuits
10kΩ
10kΩ
V
PULLUP
IN+
R
PULLUP
µC
VR
1nF
SENSOR
COUT
TPU
MAX9924
MAX9926
IN-
BIAS
1kΩ
1kΩ
10µF || 0.1µF
EXT
V
+5V
CC
ZERO_EN
INT_THRS
GND
Figure 2. MAX9924/MAX9926 Operating Mode A1
10kΩ
V
PULLUP
IN+
R
PULLUP
µC
VR
SENSOR
1nF
COUT
TPU
10kΩ
IN-
MAX9924
MAX9926
BIAS
EXT
V
+5V
CC
ZERO_EN
INT_THRS
GND
Figure 3. MAX9924/MAX9926 Operating Mode A2
Maxim Integrated
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Application Circuits (continued)
10kΩ
V
PULLUP
IN+
R
PULLUP
µC
VR
SENSOR
1nF
COUT
TPU
10kΩ
MAX9924
MAX9926
IN-
PWM
BIAS
1kΩ
1kΩ
10µF || 0.1µF
EXT
FILTER
V
+5V
CC
ZERO_EN
INT_THRS
GND
Figure 4. MAX9924/MAX9926 Operating Mode B
10kΩ
V
PULLUP
IN+
R
PULLUP
µC
VR
SENSOR
1nF
COUT
TPU
10kΩ
MAX9924
MAX9926
IN-
R2
BIAS
1kΩ
1kΩ
10µF || 0.1µF
EXT
V
+5V
CC
INT_THRS
ZERO_EN
R1
GND
Figure 5. MAX9924/MAX9926 Operating Mode C
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Application Circuits (continued)
10kΩ
V
PULLUP
OUT
IN-
R
PULLUP
VR
SENSOR
1nF
µC
10kΩ
COUT
TPU
IN+
MAX9925
MAX9927
BIAS
EXT
1kΩ
1kΩ
10µF || 0.1µF
V
+5V
CC
ZERO_EN
INT_THRS
GND
Figure 6. MAX9925/MAX9927 Operating Mode A
10kΩ
V
PULLUP
OUT
IN-
R
PULLUP
VR
SENSOR
1nF
µC
10kΩ
COUT
TPU
IN+
MAX9925
MAX9927
PWM
BIAS
EXT
FILTER
1kΩ
1kΩ
10µF || 0.1µF
V
+5V
CC
ZERO_EN
INT_THRS
GND
Figure 7. MAX9925/MAX9927 Operating Mode B
Maxim Integrated
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Application Circuits (continued)
10kΩ
V
PULLUP
OUT
IN-
R
PULLUP
VR
SENSOR
1nF
µC
10kΩ
COUT
TPU
IN+
MAX9925
R2
BIAS
EXT
1kΩ
1kΩ
10µF || 0.1µF
V
+5V
CC
INT_THRS
ZERO_EN
R1
GND
Figure 8. MAX9925 Operating Mode C
Maxim Integrated
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Typical Operating Circuit
4.5V TO 5.5V
V
CC
100kΩ
V
CC
100kΩ
100kΩ
MAX9924
IN-
V
CC
V
PULLUP
VR SENSOR
OP AMP
IN+
µC
R
PULLUP
COUT
100kΩ
85ms
WATCHDOG
COMPARATOR
TPU
BANDGAP
REFERENCE
VOLTAGE = 2 x V
BG
BUFFER
30%
BIAS
V
CC
PEAK
DETECTOR
10kΩ
ZERO_EN
V
MODE
LOGIC
MIN
THRESHOLD
MODE
LOGIC
*THE MAX9924 IS
CONFIGURED IN MODE A2.
INT_THRS
GND
EXT
Maxim Integrated
│ 19
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Pin Configurations
TOP VIEW
+
+
IN_THRS1
IN_THRS1
1
2
3
4
5
6
7
8
16 IN1+
15 IN1-
1
2
3
4
5
6
7
8
16 IN1+
15 IN1-
EXT1
BIAS1
EXT1
BIAS1
14
V
CC
14 V
CC
COUT1
COUT2
BIAS2
13 ZERO_EN
12 DIRN
11 GND
COUT1
COUT2
BIAS2
13 OUT1
12 OUT2
11 GND
10 IN2-
MAX9926
MAX9927
EXT2
10 IN2-
EXT2
INT_THRS2
9
IN2+
INT_THRS2
9
IN2+
QSOP
QSOP
+
+
IN+
IN-
1
2
3
4
5
10
9
V
IN+
IN-
1
2
3
4
5
10
9
V
CC
CC
INT_THRS
EXT
INT_THRS
EXT
MAX9924
µMAX
MAX9925
µMAX
N.C.
BIAS
GND
8
OUT
BIAS
GND
8
7
COUT
7
COUT
6
ZERO_EN
6
ZERO_EN
Selector Guide
Chip Information
PROCESS: BiCMOS
PART
AMPLIFIER
GAIN
1V/V
MAX9924UAUB
MAX9925AUB
MAX9926UAEE
MAX9927AEE
1 x Differential
1 x Operational
2 x Differential
2 x Operational
Externally Set
1V/V
Externally Set
Maxim Integrated
│ 20
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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.
PACKAGE TYPE
10 µMAX
PACKAGE CODE
U10+2
OUTLINE NO.
21-0061
LAND PATTERN NO.
90-0330
16 QSOP
E16+1
21-0055
90-0167
Maxim Integrated
│ 21
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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.
Maxim Integrated
│ 22
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MAX9924–MAX9927
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
DESCRIPTION
CHANGED
0
1
10/08
Initial release
—
Removed future product references for the MAX9926 and MAX9927, updated
EC table
2/09
1–4
2
3
4
5
3/09
3/11
3/12
6/18
Corrected various errors
2, 3, 4, 6, 13
Updated Figures 6, 7, and 8
17, 18
1
Added automotive qualifies parts
Added Input Filter Considerations section
14
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
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
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