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APPLICATION INFORMATION

A19520 / ATS19520 SENSOR IC OUTPUTSUNDER VIBRATION CONDITIONS
By Kevin Maffei
Allegro MicroSystems

INTRODUCTION
This application note details the Allegro A19520 and ATS19520
sensor IC outputs for general target and sensor vibration
scenarios.

SENSOR OPTIONS
The following character pairs, as observed in A/ATS19520
datasheets, will be outlined throughout the document:

A19520LUB
2-Pin SIP
(package suffix UB)

Not to scale• Vibration Immunity/Direction Change:
L – Low vibration immunity with immediate directionchange detection
H – High vibration immunity• Running Mode Non-Direction Pulses
B – Blanked, no output during Running mode

ATS19520LSN
3-Pin SIP with integrated
back-biased magnet(package suffix SN)

Not to scale

P – Pulses allowed during Running mode
• Calibration Mode Non-Direction Pulses
O – Blanked, no output during Calibration
Y – Pulses allowed during Calibration

VIBRATION DEFINITION
Oscillatory (back-and-forth) motion of the target angle or air
gap position without net displacement. Vibration consideredis either angular or air gap variation, and not the combinationof the two. Sensor outputs contained herein are only for inspecification target and sensor motions.

IMMUNITY DEFINITION
Air Gap

Figure 1: Air Gap

The sensor shall not have unexpected output direction pulses
when exposed only to air gap or angular vibration with amplitude at least up to datasheet specified values.

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APPLICATION INFORMATIONTCYCLE DEFINITION

Ferromagnetic Target
Tooth

This Allegro-specific term is used when the sensed target has
the same tooth-valley pitch around its circumference. When
this condition is true, it is valid to specify multiple tooth-valley
pairs as (n × TCYCLE) because each TCYCLE is the same amountof angular target rotation. Looking at Figure 2, a single TCYCLE isobserved as one “peak” of BDIFF to an immediate next “peak” of
BDIFF. Figure 2 shows a single BDIFF channel. In the A/ATS19520,
two channels exist and are referred to as “Channel A” and“Channel B”.

ValleyTCYCLE

BDIFF

Figure 2: TCYCLE Reference

AIR GAP VIBRATION DEFINITION
Air gap vibration is defined as vibration of the distance between the sensor and a stationary target. Reference Figure 1 indicating
how air gap is determined, and Figure 3 which depicts example magnetic signals of the A/ATS19520 under this air gap vibration
condition. This example shows the two sensor channels are experiencing a 180° out-of-phase signal relationship during the air gap
only vibration sequence. Air gap vibrations do not always have this effect; magnetic channels are impacted differently based on theposition of the tooth versus the sensor. Each magnetic channel of the A/ATS19520 are differential, making it an “edge detector”;
therefore, air gap vibrations over a tooth edge will have a much larger impact as compared to any other location on the target.
Normal Rotation
Magnetic Flux Density

Normal RotationBB

D IF FD IF F, Channel A, Channel B

Air Gap Vibration
with zero angular rotation
0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

Sim time (s)Figure 3: Magnetic profiles for example of air gap vibration

ANGULAR VIBRATION DEFINITON
Angular vibration is defined as vibration of only the target angular motion. Reference Figure 4 which depicts the magnetic signalsof the A/ATS19520 under this target angular vibration condition. This example shows target angular motion where the maximum
amount of rotation between each direction change is less than 1 TCYCLE.
Direction Change = --------

Normal Rotation

Magnetic Flux Density

Normal Rotation

BB

0.005

0.01

0.015

0.02

D IF FD IF F, Channel A, Channel B

0.025

Sim time (s)Figure 4: Target angular vibration example

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APPLICATION INFORMATION

Calibration ModeCalibration mode is the state the sensor starts at immediately following a power-on event. In this mode of operation, the sensor
is in the process of validating target direction and is already in a state of “vibration detected”. Due to this condition, the immunity
to vibrating stimulus, whether it be air gap or angular motion, will be the same for both “-L” and “-H” options with performance
attributes matching that of “-H” in running mode. From the datasheet, it is guaranteed the sensor will give proper direction
information by 4 TCYCLE, given continuous target rotation of the same direction. The option exists to blank or give non-directional
pulses in Calibration mode; see Figure 5. Upon the delivery of proper direction information, the sensor will leave Calibration
mode and enter Running mode.

I CC(HIGH)

Outputt W(FWD)I CC(LOW)

OutputI RESETI CC(LOW)I RESET
0.004

0.006

Magnetic Flux Density

0.002BB

0.002

0.004

D IF FD IF F, Channel A, Channel B

0.002

0.004

0.006

0.002

0.004

0.006

Magnetic Flux Density

OutputI CC(HIGH)

0.006

Figure 5: Calibration mode “-O” vs. “-Y”

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APPLICATION INFORMATION“-H” and “-L” with Air Gap Vibration (Running Mode)
For an air gap only vibration scenario, the A/ATS19520 will be immune to giving repeated directional pulse information. The“-H” and “-L” options may have different behavior.Reference Figure 6 where the sensor IC output is observed showing no direction information communicated between time 7.2 to 14.7 ms. The “-P” option is allowing for non-directional pulses to persist if
Channel A is crossing the calculated switch point during the detected vibration sequence. For the case of the “-L” option, Figure
7 shows a directional pulse was communicated by the sensor IC during air gap vibration. Because this is the “-L” option, a singlepulse occurrence during the sequence may occur.
Air gap vibration
I CC(HIGH)

OutputOutputt W(FWD)I CC(LOW)t W(ND)I RESET
0.004

0.006

0.008

0.01

0.012

0.014

Air gap vibra�on

0.018

0.02

Normal Rota�on

Magnetic Flux Density

Normal Rota�on

0.016

B
B

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

D IF FD IF F, Channel A, Channel B

0.02

Sim time (s)Figure 6: “-HP” option under air gap vibration (non-direction pulses are blanked for “-HB” option)Air gap vibration

OutputI CC(HIGH)

Single direc�onpulse allowedOutputt W(FWD)

I CC(LOW)t W(REV)I RESET
0.004

0.006

0.008

0.01

0.012

0.014

Air gap vibra�on

0.018

0.02

Normal Rota�on

Magnetic Flux Density

Normal Rota�on

0.016

B
B

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

D IF FD IF F, Channel A, Channel B

0.02

Sim time (s)Figure 7: “-LB” option under air gap vibration (non-direction pulses may be output depending on magnetic signal profile for the “-LP” option)

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APPLICATION INFORMATION“-H” and “-L” with Angular Vibration (Running Mode)
Angular target motion captures a clear picture of the performance difference between the “-L” and “-H” options. The “-H”
option observed in Figure 8, is designed to immediately detect vibration, which means that any time the sensor observes asingle change in direction, it will cease to communicate direction information until a target rotational movement of continuous
direction for 3.5 TCYCLE [1] (worst case) is observed. The key advantage of this option is if 1 TCYCLE or less of angular vibration isoccurring, no directional information will be communicated during this vibration.

Angular vibration
I CC(HIGH)

OutputOutputt W(REV)I CC(LOW)t W(ND)I RESET
0.004

0.006

0.008

0.012

0.014

0.016

0.018

Direc�on Change = -------

0.02

0.022

Normal Rota�on

Magnetic Flux Density

Normal Rota�on0.01

BB

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

D IF FD IF F, Channel A, Channel B

0.022

Sim time (s)Figure 8: “-HP” option under angular vibration[1] Based on Allegro Reference Target 60-0 (see ATS19520 datasheet).

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APPLICATION INFORMATION

The “-L” option observed in Figure 9 is designed to delay the detection of vibration until two direction changes are detected
within five switch point crossings on Channel A. This means vibration detection may be delayed until 2.5 TCYCLE [1], although aftervibration is detected by the sensor, the 1 TCYCLE immunity remains. This “delayed detection” is seen in Figure 9, where at thebeginning of the angular vibration sequence, a single reverse direction pulse is communicated. Because this is the “-L” option,a single pulse occurrence during the vibration sequence is expected. The key advantage of this option is the single directionchange case because the indication of a target direction change occurs as soon as a switch point on Channel A is crossed.

Angular vibration
I CC(HIGH)

OutputFirst direc�on change
communicatedOutputt W(FWD)t W(REV)I CC(LOW)t W(ND)I RESET
0.004

0.006

0.008

0.012

0.014

0.016

0.018

Direc�on Change = -------

0.02

0.022

Normal Rota�on

Magnetic Flux Density

Normal Rota�on

0.01

B
B

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

D IF FD IF F, Channel A, Channel B

0.022

Sim time (s)Figure 9: “-LB” behavior under angular vibration[1] Based on Allegro Reference Target 60-0 (see ATS19520 datasheet).

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APPLICATION INFORMATION

Revision History
NumberDate

Description

Responsibility–

September 23, 2021

Initial release

K. Maffei

Copyright 2021, Allegro MicroSystems.

The information contained in this document does not constitute any representation, warranty, assurance, guaranty, or inducement by Allegro to the customer with respect to the subject matter of this document. The information being provided does notguarantee that a process based on this information will be reliable, or that Allegro has explored all of the possible failure modes.
It is the customer’s responsibility to do sufficient qualification testing of the final product to ensure that it is reliable and meetsall design requirements.
Copies of this document are considered uncontrolled documents.

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