MAX9927AEE/V+ [MAXIM]
Variable Reluctance Sensor Interfaces with Differential Input and Adaptive Peak Threshold; 可变磁阻传感器接口，提供差分输入和自适应峰值门限
| 型号： | MAX9927AEE/V+ |
| 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：340K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-4283; Rev 4; 3/12
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
General Description
Features
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.
o Differential Input Stage Provides Enhanced Noise
Immunity
o Precision Amplifier and Comparator Allows
Small-Signal Detection
o User-Enabled Internal Adaptive Peak Threshold or
Flexible External Threshold
o Zero-Crossing Detection Provides Accurate
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.
Phase Information
Ordering Information
PART
TEMP RANGE
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
PIN-PACKAGE
MAX9924UAUB+
MAX9924UAUB/V+
MAX9925AUB+
MAX9926UAEE+
MAX9926UAEE/V+
MAX9927AEE+
MAX9927AEE/V+
10 µMAX
10 µMAX
10 µMAX
16 QSOP
16 QSOP
16 QSOP
16 QSOP
-40°C to +125°C
-40°C to +125°C
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.
+Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
Applications
Camshaft VRS Interfaces
Crankshaft VRS Interfaces
Vehicle Speed VRS Interfaces
µMAX is a registered trademark of Maxim Integrated Products, Inc.
Simplified Block Diagram
ENGINE BLOCK
MAX9924
DIFFERENTIAL
AMPLIFIER
VR SENSOR
μC
ADAPTIVE/MINIMUM
AND
ZERO-CROSSING
THRESHOLDS
INTERNAL/EXTERNAL
BIAS VOLTAGE
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
ABSOLUTE MAXIMUM RATINGS
CC
All Other Pins..............................................-0.3V to (V
Current into IN+, IN-, IN_+, IN_-.......................................±±0mA
Current into All Other Pins ................................................±20mA
Output Short-Circuit (OUT_, OUT) to GND.............................10s
V
to GND.............................................................-0.3V to + 6V
Operating Temperature Range .........................-±0°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.
PACKAGE THERMAL CHARACTERISTICS (Note 1)
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 )................±2°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 www.maxim-ic.com/thermal-tutorial.
4–MAX927
ELECTRICAL CHARACTERISTICS
(V
= 5V, V
= 0V, MAX9925/MAX9927 gain setting = 1V/V, Mode A1, V
= 2.5V, V
= 5V, R
= 1kΩ, C
=
CC
GND
BIAS
PULLUP
PULLUP
COUT
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)
±.5
5.5
5
V
CC
MAX992±/MAX9925
MAX9926/MAX9927
2.6
±.7
Supply Current
I
mA
CC
10
V
> V
= ±.1V, step time for V
UVLO CC
CC
Power-On Time
P
30
150
µs
ON
~ 1µs
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 ±)
(Note ±)
BIAS
Input Offset Current
I
0.05
102
105
nA
OFFSET
Common-Mode Rejection Ratio
CMRR
From V
= 0 to V
75
88
77
dB
CM
CC
MAX9925
MAX9927
Power-Supply Rejection Ratio
PSRR
dB
9±
Output Voltage Low
Output Voltage High
V
I
= 1mA
0.050
V
V
OL
OL
V
-
CC
V
I
= -1mA
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
SR
1.±
2.3
1.3
MHz
V/µs
MHz
Charge-Pump Frequency
f
CP
2
_______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
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
MAX9924/MAX9925
MAX9926/MAX9927
-6.5
-6.5
0
+6.5
+10
Mode B
operation
(Notes 5, 6)
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
Overdrive = 2V to 3V, adaptive peak
t
50
150
2
PDZ
Propagation Delay
ns
ns
t
PDA
COUT Transition Time
t
HL-LH
Includes noise of differential amplifier
and comparator, f = 10kHz,
Propagation Delay Jitter
t
20
ns
PD-JITTER
V
= 1V
sine wave
IN
P-P
_______________________________________________________________________________________
3
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
BIAS
10
µA
V
EXT
EXT
0.2
0.3 x
Low Input
V
V
IL
V
CC
0.7 x
4–MAX927
High Input
V
V
IH
V
CC
Input Leakage
I
1
µA
LEAK
Pullup resistor = 10kΩ,
= V
Input Current ZERO_EN
I
500
3
800
µA
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
4
_______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
Typical Operating Characteristics
(V
= 5V, V
= 0V, MAX9925/MAX9927 gain setting = 1V/V. All values are at T = +25°C, unless otherwise noted.)
GND A
CC
INPUT OFFSET VOLTAGE
vs. INPUT COMMON-MODE VOLTAGE
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
INPUT OFFSET VOLTAGE DISTRIBUTION
20
15
10
5
0.5
0.4
0.3
0.2
0.1
0
120
100
80
60
40
20
0
V
= 0
CM
BIN SIZE = 250
V
V
= V
= 2V
= 2.5V
OUT
P-P
BIAS
CM
V
= 2.5V
OUT
MAX9925
CMRR = 20log(A /A
)
DM CM
0
0
2000
2500
-2000 -1000
1000
3000
-0.5
0.5
1.5
2.5
3.5
4.5
5.5
1
10
100
1k
10k
100k
-500
500
1500
-1500
INPUT COMMON-MODE VOLTAGE (V)
FREQUENCY (Hz)
INPUT OFFSET VOLTAGE (μV)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
OPEN LOOP FREQUENCY
RESPONSE
V
OL
AND V vs. TEMPERATURE
OH
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
40
35
125
100
75
50
25
0
V
V
= 100mV
P-P
RIPPLE
BIAS
V
V
V
= 5V
CC
= V
= 2.5V
OUT
= 2.5V
BIAS
INPUTS COUPLED TO GND
= 2V
OUT
P-P
30
25
MAX9925
V
- V
OH
CC
20
15
10
5
V
OL
-100
-110
-120
0
1
10
100
1k
10k
100k
-50 -25
0
25
50
75 100 125
0.001
0.1
FREQUENCY (kHz)
10
FREQUENCY (Hz)
TEMPERATURE (°C)
ADAPTIVE THRESHOLD
vs. TEMPERATURE
INPUT OFFSET VOLTAGE
vs. TEMPERATURE
ADAPTIVE THRESHOLD AND RATIO
vs. SIGNAL LEVEL
400
350
900
0.6
0.5
0.4
0.3
0.2
0.1
0
V
= 2.5V
OUT
800
700
600
500
400
300
200
100
0
MAX9925
300
250
V
= 0
CM
200
150
100
V
= 2.5V
CM
V
= 2V
P-P
IN
f
= 1kHz
IN
50
0
f
= 1kHz
IN
MAX9924
MAX9924
-50 -25
0
25
50
75 100 125
-50 -25
0
25
50
75 100 125
0
0.5
1.0
1.5
2.0
2.5
TEMPERATURE (°C)
TEMPERATURE (°C)
SIGNAL LEVEL (V )
P
_______________________________________________________________________________________
5
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.)
GND A
CC
MINIMUM AND ZERO-CROSSING
THRESHOLD vs. TEMPERATURE
INPUT SIGNAL vs. COUT WITH
WATCHDOG TIMER EXPIRED
CMRR vs. TEMPERATURE
MAX9924 toc12
30
25
20
15
10
5
100
75
50
25
0
COUT
V
= 2.5V
= 5Hz
CM
INPUT SIGNAL
MINIMUM THRESHOLD
f
IN
5V
V
BIAS
ZERO CROSSING
AT 5Hz
ZERO CROSSING
AT 1Hz
0
MAX9924
V
= 0 TO 5V
f
= 5Hz
CM
IN
-5
4–MAX927
-50 -25
0
25
50
75 100 125
-50 -25
0
25
50
75 100 125
20ms/div
TEMPERATURE (°C)
TEMPERATURE (°C)
INPUT SIGNAL vs. COUT WITH
WATCHDOG TIMER EXPIRED
OVERDRIVEN INPUT VOLTAGES
(MAX9924)
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)
6
_______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
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
8
7
8
—
—
—
—
COUT
.
PULLUP
External Reference Input. Leave EXT unconnected in Modes
A1, A2. Apply an external voltage in Modes B, C.
EXT
9
9
—
14
1
—
14
1
INT_THRS
Internal Adaptive Threshold. Mode configuration pin.
Power Supply
10
—
10
—
V
CC
INT_THRS1
Internal Adaptive Threshold 1. Mode configuration pin.
External Reference Input 1. Leave EXT unconnected in Modes
A1, A2. Apply an external voltage in Modes B, C.
—
—
—
—
—
—
—
—
—
—
—
—
2
3
4
5
6
7
2
3
4
5
6
7
EXT1
Input Bias 1. Connect to an external resistor-divider and
bypass to ground with a 0.1µF and 10µF capacitor.
BIAS1
COUT1
COUT2
BIAS2
EXT2
Comparator Output 1. Open-drain output, connect a 10kΩ
pullup resistor from COUT1 to V
.
PULLUP
Comparator Output 2. Open-drain output, connect a 10kΩ
pullup resistor from COUT2 to V
.
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
IN2+
Internal Adaptive Threshold 2. Mode configuration pin.
Noninverting Input 2
10
10
IN2-
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+
_______________________________________________________________________________________
7
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Functional Diagrams
100kΩ
V
CC
V
CC
100kΩ
100kΩ
IN-
IN+
V
CC
MAX9924
OP AMP
GND
100kΩ
65ms
WATCHDOG
COMPARATOR
COUT
INTERNAL
REFERENCE
2.5V
4–MAX927
BUFFER
30%
V
CC
BIAS
PEAK
DETECTOR
10kΩ
MODE
LOGIC
V
MIN
ZERO_EN
INT_THRS
THRESHOLD
MODE
LOGIC
INT_THRS
EXT
8
_______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
Functional Diagrams (continued)
OUT
V
CC
V
CC
IN-
IN+
V
CC
MAX9925
OP AMP
GND
85ms
WATCHDOG
COMPARATOR
COUT
BIAS
BUFFER
30%
V
CC
PEAK
DETECTOR
10kΩ
V
MIN
MODE
LOGIC
ZERO_EN
INT_THRS
THRESHOLD
EXT
_______________________________________________________________________________________
9
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Functional Diagrams (continued)
100kΩ
V
CC
V
CC
100kΩ
100kΩ
IN1-
IN1+
V
CC
MAX9926
OP AMP
GND
100kΩ
85ms
WATCHDOG
COMPARATOR
COUT1
INTERNAL
REFERENCE
2.5V
BUFFER
4–MAX927
30%
BIAS1
PEAK
DETECTOR
CLK
V
MIN
DIRN
DIRN
FLIP-FLOP
THRESHOLD
EXT1
100kΩ
V
CC
100kΩ
100kΩ
IN2-
IN2+
V
CC
OP AMP
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
10 ______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
Functional Diagrams (continued)
OUT1
V
CC
V
CC
IN1-
IN1+
V
CC
MAX9927
OP AMP
GND
85ms
WATCHDOG
COMPARATOR
COUT1
BIAS1
BUFFER
30%
PEAK
DETECTOR
V
MIN
THRESHOLD
EXT1
V
CC
IN2-
IN2+
V
CC
OP AMP
OUT1
85ms
WATCHDOG
COMPARATOR
COUT2
BIAS2
BUFFER
30%
INT_THRS1
INT_THRS2
MODE
LOGIC
PEAK
DETECTOR
V
MIN
THRESHOLD
EXT2
______________________________________________________________________________________ 11
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
ing the output of the input differential amplifier with a
Detailed Description
threshold voltage that is set depending on the mode
The MAX9924–MAX9927 interface with variable reluc-
that the device is in (see the Mode Selection section).
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.
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).
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-
4–MAX927
Table 1. MAX9924/MAX9926 Operating Modes
SETTING
DEVICE FUNCTIONALITY
OPERATING MODE
ADAPTIVE PEAK
THRESHOLD
BIAS VOLTAGE
SOURCE
ZERO_EN
INT_THRS
ZERO CROSSING
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
CC
GND
C
GND
V
CC
Table 3. MAX9927 Operating Modes
SETTING
DEVICE FUNCTIONALITY
OPERATING MODE
INT_THRS
ZERO CROSSING
Enabled
ADAPTIVE PEAK THRESHOLD
A1
B
V
Enabled
Disabled
CC
GND
Enabled
12 ______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
Differential Amplifier
The input operational amplifier is a rail-to-rail input and
output precision amplifier with CMOS input bias cur-
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.
rents, low offset voltage (V ) and drift. A novel input
OS
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.
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).
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 sta-
ble external BIAS reference.
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 (V ). This ensures pulse
MIN_THRESH
recognition recovers even in the presence of intermit-
tent sensor connection.
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.
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.
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
______________________________________________________________________________________ 13
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
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.
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.
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.
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.
4–MAX927
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,
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
⎛
⎞
R1(V
R1+R2+R
− V
)
PULLUP
BIAS
V
=
+ V
BIAS
TH
⎜
⎟
⎝
⎠
PULLUP
between the V
and GND pins. The connection
CC
and
between these capacitor terminals and the power-sup-
ply pins of the part (both V and GND) should be
R2
R1+R2
⎛
⎞
⎠
CC
V
=
× V
⎜
⎝
⎟
TL
BIAS
through wide traces (preferably planes), and without
vias in the high-frequency current path.
14 ______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
Application Circuits
10kΩ
10kΩ
V
PULLUP
IN+
R
PULLUP
μC
VR
1nF
SENSOR
COUT
TPU
IN-
MAX9924
MAX9926
BIAS
1kΩ
1kΩ
10μF || 0.1μF
EXT
V
CC
+5V
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
CC
+5V
ZERO_EN
INT_THRS
GND
Figure 3. MAX9924/MAX9926 Operating Mode A2
______________________________________________________________________________________ 15
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Application Circuits (continued)
10kΩ
10kΩ
V
PULLUP
IN+
R
PULLUP
μC
VR
1nF
SENSOR
COUT
TPU
IN-
PWM
MAX9924
MAX9926
BIAS
1kΩ
1kΩ
10μF || 0.1μF
EXT
FILTER
V
+5V
CC
ZERO_EN
INT_THRS
GND
4–MAX927
Figure 4. MAX9924/MAX9926 Operating Mode B
10kΩ
V
PULLUP
IN+
R
PULLUP
μC
VR
SENSOR
1nF
COUT
TPU
10kΩ
IN-
MAX9924
MAX9926
R2
BIAS
1kΩ
1kΩ
10μF || 0.1μF
EXT
V
+5V
CC
INT_THRS
ZERO_EN
R1
GND
Figure 5. MAX9924/MAX9926 Operating Mode C
16 ______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
Application Circuits (continued)
10kΩ
10kΩ
V
PULLUP
OUT
IN-
IN+
R
PULLUP
VR
SENSOR
1nF
μC
COUT
TPU
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-
IN+
R
PULLUP
VR
SENSOR
1nF
μC
10kΩ
COUT
TPU
PWM
MAX9925
MAX9927
BIAS
EXT
FILTER
1kΩ
1kΩ
10μF || 0.1μF
V
+5V
CC
ZERO_EN
INT_THRS
GND
Figure 7. MAX9925/MAX9927 Operating Mode B
______________________________________________________________________________________ 17
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
Application Circuits (continued)
10kΩ
10kΩ
V
PULLUP
OUT
IN-
R
PULLUP
VR
SENSOR
1nF
μC
COUT
TPU
IN+
MAX9925
R2
BIAS
EXT
1kΩ
1kΩ
10μF || 0.1μF
V
+5V
CC
4–MAX927
INT_THRS
ZERO_EN
R1
GND
Figure 8. MAX9925 Operating Mode C
18 ______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
Typical Operating Circuit
4.5V TO 5.5V
V
CC
100kΩ
V
CC
100kΩ
100kΩ
IN-
IN+
V
CC
MAX9924
V
PULLUP
VR SENSOR
OP AMP
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
______________________________________________________________________________________ 19
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
MAX9926
13 ZERO_EN
12 DIRN
11 GND
COUT1
COUT2
BIAS2
MAX9927
13 OUT1
12 OUT2
11 GND
10 IN2-
EXT2
10 IN2-
EXT2
INT_THRS2
9
IN2+
INT_THRS2
9
IN2+
QSOP
QSOP
4–MAX927
TOP VIEW
+
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
N.C.
BIAS
GND
8
OUT
BIAS
GND
8
MAX9924
MAX9925
7
COUT
7
COUT
6
ZERO_EN
6
ZERO_EN
μMAX
μMAX
Chip Information
Selector Guide
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
20 ______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
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.
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
α
α
______________________________________________________________________________________ 21
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.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.
4–MAX927
22 ______________________________________________________________________________________
Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
4–MAX927
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
DESCRIPTION
0
1
10/08
2/09
Initial release
—
Removed future product references for the MAX9926 and MAX9927, updated EC
table
1–4
2
3
3/09
3/11
3/12
Corrected various errors
2, 3, 4, 6, 13
17, 18
Updated Figures 6, 7, and 8
Added automotive qualifies parts
4
1
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
© 2012 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
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