MAX9924UAUB+ Maxim Integrated Products, MAX9924UAUB+ Datasheet - Page 13

• Manufacturer Part Number: MAX9924UAUB+
• Description: IC SENSOR INTERFACE VARI 10MSOP
• Manufacturer: Maxim Integrated Products
• Type: Sensor Interfacer

Specifications of MAX9924UAUB+

• Input Type: Differential
• Output Type: Logic
• Interface: Differential
• Current - Supply: 5mA
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The input operational amplifier is a rail-to-rail input and
output precision amplifier with CMOS input bias cur-
rents, low offset voltage (V
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.
In Modes A1, B, and C, a well-decoupled external
resistor-divider generates a V
input that is used to reference all internal electronics in
the device. BIAS should be bypassed with a 0.1µF and
10µF capacitor in parallel with the lower half of the
resistor-divider forming a lowpass filter to provide a sta-
ble external BIAS reference.
The minimum threshold, adaptive peak threshold, zero-
crossing threshold signals are all referenced to this
voltage. An input buffer eliminates loading of resistor-
dividers due to differential amplifier operation. Connect
BIAS to ground when operating in Mode A2. An internal
(2.5V typical) reference is used in Mode A2, eliminating
external components.
Figure 1. Adaptive Peak Threshold Operation
Differential Input and Adaptive Peak Threshold
SIGNAL
COUT
Variable Reluctance Sensor Interfaces with
VR
______________________________________________________________________________________
V1
20ms
OS
Differential Amplifier
1
3
) and drift. A novel input
V1
CC
40ms
/2 signal for the BIAS
THRESHOLD
ADAPTIVE
SET BY V1
Bias Reference
60ms
V2
80ms
100ms
Modes A1 and A2 in the MAX9924–MAX9927 use an
internal adaptive peak threshold voltage to trigger the
output comparator. This adaptive peak threshold volt-
age scheme provides robust noise immunity to the input
VR signal, preventing false triggers from occurring due
to broken tooth or off-centered gear-tooth wheel. See
Figure 1.
The sensor signal at the output of the differential gain
stage is used to generate a cycle-by-cycle adaptive
peak threshold voltage. This threshold voltage is 1/3 of
the peak of the previous cycle of the input VR signal. As
the sensor signal peak voltage rises, the adaptive peak
threshold voltage also increases by the same ratio.
Conversely, decreasing peak voltage levels of the input
VR signal causes the adaptive peak threshold voltage
used to trigger the next cycle also to decrease to a new
lower level. This threshold voltage then provides an
arming level for the zero-crossing circuit of the com-
parator (see the Zero Crossing section).
If the input signal voltage remains lower than the adap-
tive peak threshold for more than 85ms, an internal
watchdog timer drops the threshold level to a default
minimum threshold (V
recognition recovers even in the presence of intermit-
tent sensor connection.
The internal adaptive peak threshold can be disabled
and directly fed from the EXT input. This mode of opera-
tion is called Mode B, and allows implementations of cus-
tom threshold algorithms in firmware. This EXT voltage is
typically generated by filtering a PWM-modulated output
from an onboard microcontroller (µC). An external opera-
tional amplifier can also be used to construct an active
lowpass filter to filter the PWM-modulated EXT signal.
1/3 V2
120ms
THRESHOLD
SET BY V2
ADAPTIVE
85ms
140ms
MIN_THRESH
Adaptive Peak Threshold
160ms
). This ensures pulse
THRESHOLD
180ms
MIN
200ms
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