ACS712 — Fully Integrated Hall-Effect Linear Current Sensor IC

Overview

The ACS712 is a fully integrated Hall-effect linear current sensor IC manufactured by Allegro MicroSystems. It measures both AC and DC current by sensing the magnetic field generated when current flows through an internal $1.2\text{ m}\Omega$ copper conduction path.

Because the current path is electrically isolated from the sensor electronics, the ACS712 provides $2.1\text{ kV}_{\text{RMS}}$ galvanic isolation, making it safe for measuring high-voltage AC loads (such as household appliances or motors) with low-voltage microcontrollers.

Quick reference


Operating Voltage (`VCC`)	4.5 V to 5.5 V DC (5.0 V nominal)
Output Offset Voltage	$V_{CC} / 2$ ( $2.50\text{ V}$ at 0 Amperes current)
Galvanic Isolation Voltage	$2.1\text{ kV}_{\text{RMS}}$ (50/60 Hz for 1 minute)
Conductor Resistance	$1.2\text{ m}\Omega$ (ultra-low power loss)
Bandwidth	80 kHz
Variant Current Ratings	5 A variant (`185 mV/A`), 20 A variant (`100 mV/A`), 30 A variant (`66 mV/A`)
Output Type	Ratiometric Analog Voltage (`OUT`)

Variant Sensitivity Comparison

Variant Part Number	Max Current Range	Sensitivity ( $S$ )	Zero Current Output ( $V_{OUT,0}$ )
ACS712-05B	$\pm 5\text{ A}$	$185\text{ mV / A}$	$2.50\text{ V}$ ( $V_{CC} / 2$ )
ACS712-20A	$\pm 20\text{ A}$	$100\text{ mV / A}$	$2.50\text{ V}$ ( $V_{CC} / 2$ )
ACS712-30A	$\pm 30\text{ A}$	$66\text{ mV / A}$	$2.50\text{ V}$ ( $V_{CC} / 2$ )

Pinout

Standard Breakout Board Header & Screw Terminal

Pin / Terminal	Name	Type	Description
Screw Terminal 1	`IP+`	High-Current Input	Conductor input (in series with AC/DC load)
Screw Terminal 2	`IP-`	High-Current Output	Conductor output (to load)
Header Pin 1	`VCC`	Power	Supply voltage (+4.5 V to +5.5 V DC)
Header Pin 2	`GND`	Power	Ground (0 V)
Header Pin 3	`OUT`	Analog Output	Analog output voltage proportional to current

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Supply Voltage	$V_{CC}$	4.5	5.0	5.5	V	DC
Supply Current	$I_{CC}$	—	10	13	mA	$V_{CC} = 5.0\text{ V}$
Sensitivity Error	$E_{SENS}$	—	$\pm 1.5$	—	%	$T_A = 25^\circ\text{C}$
Total Output Error	$E_{TOT}$	—	$\pm 1.5$	$\pm 4.0$	%	$I_{P} = I_{P,max}$
Response Time	$t_{response}$	—	5	—	µs	Output rise time to 90%
Frequency Bandwidth	$BW$	—	80	—	kHz	$C_{FILTER} = 1\text{ nF}$

Current Measurement Formulas

DC Current Formula

$I_{DC}\text{ (Amperes)} = \frac{V_{OUT}\text{ (in mV)} - 2500\text{ mV}}{\text{Sensitivity } S\text{ (in mV/A)}}$

Example for ACS712-05B ( $185\text{ mV/A}$ ) with a $2.87\text{ V}$ ADC output reading:

$I_{DC} = \frac{2870\text{ mV} - 2500\text{ mV}}{185\text{ mV/A}} = \frac{370}{185} = +2.0\text{ A}$

AC RMS Current Formula

For 50/60 Hz AC current, sample $V_{OUT}$ over several full AC wave cycles ( $\sim 100\text{ ms}$ ), find the peak-to-peak voltage ( $V_{pp}$ in mV), and calculate RMS current:

$I_{RMS} = \left(\frac{V_{pp}\text{ (in mV)}}{2 \sqrt{2}}\right) \div \text{Sensitivity } S\text{ (in mV/A)}$

Wiring

text

           [ ACS712 Screw Terminal ]
           │                       │
     AC/DC Power (+ Line)       AC/DC Load (+ Line)

ACS712 Breakout Pin	→	Microcontroller (Arduino Uno / ESP32)
`VCC`		`5V`
`GND`		`GND`
`OUT`		Analog Input Pin `A0` (or ADC with voltage divider for 3.3V MCUs)

Warning

High Voltage Safety & 3.3V ADC Compatibility:

Mains AC Safety: Although the ACS712 IC provides $2.1\text{ kV}$ isolation, cheap breakout PCBs may have insufficient creepage/clearance distance between high-voltage screw terminals and logic header pins. Exercise extreme caution when measuring 110V/230V mains voltage!
3.3V Microcontrollers (ESP32/Raspberry Pi): The ACS712 outputs up to $4.5\text{ V}$ when measuring positive current. Use a $10\text{ k}\Omega / 20\text{ k}\Omega$ resistor voltage divider on OUT before connecting to 3.3V ADC inputs.

Common mistakes

External Magnetic Interference: Hall-effect sensors are sensitive to external magnetic fields. Keep motors, transformers, and heavy inductors away from the ACS712 package.
Powering from 3.3V: Operating the ACS712 on 3.3V shifts the zero-current baseline away from $2.5\text{ V}$ and reduces sensitivity non-linearly. Always power with 5.0 V DC.
Measuring small currents with 20A/30A variants: Measuring $< 500\text{ mA}$ with an ACS712-30A produces tiny voltage changes ( $33\text{ mV}$ for 0.5A) that get lost in ADC noise. Use the 5A variant or an INA219 for low-current applications.

Notes

Solder jumper / capacitor on the FILTER pin allows adjusting the high-frequency cutoff to reduce output noise.

Interface	Analog Output
Supply	4.5–5.5 V
Package	8-pin SOIC / Breakout Board with Screw Terminal