Richard Dickinson William Bentley INTRODUCTION minimum current th

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Managing Noise Levels ACS704 Current Sensor
Richard Dickinson William Bentley
INTRODUCTION minimum current that resolved ACS704 current sensor limited noise present output sensor. Resolution improved addition external filter sensor output. However, such filtering limits bandwidth response time sensor.
This application note guide evaluating trade-off resolution versus response time when using ACS704 current sensor.
NOISE SOURCES ON-BOARD FILTERING order reduce temperature drift offset sensor, axis operation Hall element switched degrees rate kHz. This "chopper" circuit source most noise sensor output. Another source "shot" noise Hall element, which very similar shot noise characteristic resistor. ACS704 on-board filter reduce this noise output signal. relatively loose tolerances which resistors capacitors fabricated semiconductor die, tolerance on-board filter ±30%. With only this on-board filter, minimum resolvable current ACS704
AN295035
Managing Noise Levels ACS704 Current Sensor
IMPROVING RESOLUTION NOISE PERFORMANCE filtering tolerances achievable using discrete external filters much tighter than tolerances available with on-board filters. external filter with lower roll-off value than on-board filter lowers noise improves available
resolution. This however, cost reducing bandwidth response time solution. following table shows noise reduction, resolution, bandwidth, response time tradeoffs that produced various values external filters. Filtering output ACS704 below minimum values this table does produce further improvements current resolution.
ACS704 Noise Filtering, Filter Values, Frequency Response Performance
Break Frequency Filter (kHz) Resistance Capacitance (µF) Nominal Programmed Filtered Peak-toSensitivity Peak Noise (mV/A) (mV) Resolution with Filtering Rise Time Step, Filtered (µs)
ACS704ELC-015 Unfiltered Unfiltered 1500 3150 4800 1500 3150 4800 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 ~0.75 ~0.46 ~0.43 ~0.25 ~0.17 ~0.12 ~0.67 ~0.42 ~0.35 ~0.20 ~0.15 ~0.10 12.5
ACS704ELC-005
AN295035
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Managing Noise Levels ACS704 Current Sensor
EXPERIMENTAL RESULTS: ACS704ELC-015 ACS704ELC-015 mounted evaluation connected with various filter
Figure ACS704ELC-015: external filtering Step response
combinations. response step peak-to-peak output voltage noise measured each combination. results shown figures 1-6.
Peak-to-peak output voltage noise
Figure ACS704ELC-015: External Filter with resistor 0.01 capacitor Step response Peak-to-peak output voltage noise
AN295035
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Managing Noise Levels ACS704 Current Sensor
Figure ACS704ELC-015: External Filter with resistor 0.01 capacitor Step response Peak-to-peak output voltage noise
Figure ACS704ELC-015: External Filter with 1500 resistor 0.01 capacitor Step response Peak-to-peak output voltage noise
AN295035
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Managing Noise Levels ACS704 Current Sensor
Figure ACS704ELC-015: External Filter with 3150 resistor 0.01 capacitor Step response Peak-to-peak output voltage noise
Figure ACS704ELC-015: External Filter with 4800 resistor 0.01 capacitor Step response Peak-to-peak output voltage noise
AN295035
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Managing Noise Levels ACS704 Current Sensor
EXPERIMENTAL RESULTS: ACS704ELC-005 ACS704ELC-015 mounted evaluation connected with various filter
Figure ACS704ELC-005: external filtering Step response
combinations. response step peak-to-peak output voltage noise measured each combination. results shown figures 7-12.
Peak-to-peak output voltage noise
Figure ACS704ELC-005: External Filter with resistor 0.01 capacitor Step response Peak-to-peak output voltage noise
AN295035
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Managing Noise Levels ACS704 Current Sensor
Figure ACS704ELC-005: External Filter with resistor 0.01 capacitor Step response Peak-to-peak output voltage noise
Figure ACS704ELC-005: External Filter with 1500 resistor 0.01 capacitor Step response Peak-to-peak output voltage noise
AN295035
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Managing Noise Levels ACS704 Current Sensor
Figure ACS704ELC-005: External Filter with 3150 resistor 0.01 capacitor Step response Peak-to-peak output voltage noise
Figure ACS704ELC-005: External Filter with 4800 resistor 0.01 capacitor Step response Peak-to-peak output voltage noise
AN295035
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Managing Noise Levels ACS704 Current Sensor
SUMMARY This application note describes trade-offs that made between noise response time (bandwidth) improve resolution
ACS704 current sensor implementation. need further assistance with your ACS704 design, please contact your local Allegro sale office touch with applications engineers.
information included herein believed accurate reliable. However, Allegro MicroSystems, Inc. assumes responsibility use; infringement patents other rights third parties which result from use. Copyright 2005, Allegro MicroSystems, Inc.
AN295035
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com

Richard Dickinson William Bentley INTRODUCTION minimum current th

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