Current detection scheme for ACS712 current sensor

The ACS712 is a low-noise, easy-to-use, cost-effective linear current sensor used in motor control, load detection and management, switched power supplies, and overcurrent fault protection, especially in applications that require electrical insulation but do not use photoelectric insulators or other expensive insulation technologies.

ACS712 Sensor

The ACS712 has a built-in accurate low-bias linear Hall sensor circuit that outputs a voltage proportional to the detected AC or DC, with a fast response time (5μs output rise time corresponding to step input current), 50kHz bandwidth, total output error of up to 4%, high output sensitivity (66mV/A to 185mV/A), and high insulation voltage.

The ACS712 comprises a copper current path near the chip surface and a clear low bias linear Hall sensor circuit. The magnetic field generated by the current flowing through the copper current path can be sensed by the Hall IC inside the chip and converted into a proportional voltage. Device accuracy is optimized by placing the magnetic signal as close as possible to the Hall sensor. At the same time, the path through which the measured current flows (the circuit between pins 1 and 2, 3 and 4) has an internal resistance of typically 1.2 mΩ and low power consumption. The insulation voltage between the measured current path and the sensor pins (5 to 8) is >2.1kVRMS, almost insulated.

The ACS712 contains a resistor RF (INT) and a buffer amplifier. The user can use the FILTER pin (pin 6), an external capacitor CF and RF (INT) to form a simple external RC low-pass filter because the internal buffer amplifier can eliminate the output attenuation caused by the chip's internal resistance and interface load dividing voltage, so the external RC low-pass filter will not The external RC low-pass filter does not affect the signal attenuation and further reduces output noise and improves low-current accuracy.

Since a single 5V supply powers the ACS712, this sensing system uses the LP2980AIM5-5 low dropout regulator, a 5V fixed voltage output low voltage LDO with enable function. 1μF capacitor at the output pin of the regulator.

BOM Analysis

The total number of BOM components for this current detection solution is 27. Among them, the ACS712 sensor chip from Allegro, using a small SOIC8 package, pins 1 and 2, 3 and 4 are built-in insurance. When detecting DC, 1 and 2, 3 and 4 are the input and output of the current to be measured, respectively. This chip is a classic Hall current sensor.

The LP2980AIM5-5 LDO chip outputs a fixed 5V voltage and comes from TI in a 5-pin SOT-23 (DBV) package with an operating temperature range of -40°C to 125°C.

As HALL components are in the center of the chip below, PCB wiring should avoid alignment and signal interference impact. In the case of high voltage and high current need to consider the creepage distance and other current signals as far away from the input current pins.

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