Hall Current 2 Click is a very accurate current measurement Click board™, which relies on the Hall effect. Its most distinctive feature is a very low series resistance of only 1.2mΩ, making this device a nearly-perfect ampere meter. The maximum current which can be measured with the Hall current 2 ranges from -12A to +12A, with optimized precision. The measurement is thermally compensated and conditioned by the integrated sections of the hall sensor IC. The result is available via the I2C interface of the high precision, 12 bit AD converter, as well as in the analog form, from the analog pin of the microBUS™, directly from the Hall effect current sensor IC. This Click board™ does not require any current sensing resistors.
Featuring a reasonably high current range that can be measured, extremely low series resistance, a clever design offering readings in both analog and digital format, and advanced Hall current sensor IC which can withstand overcurrent conditions up to five times of the nominal measuring current range, this Click board™ can be used for a wide range of measuring and monitoring in various audio applications, telecommunication applications, white goods applications, and basically in every application which requires current measurement or monitoring, working in the range of less than 100 V.
Hall Current 2 utilizes the ACS711, a Hall effect linear current sensor with overcurrent fault output for less than 100 V Isolation Applications, from Allegro Microsystems. This sensor utilizes the Hall effect phenomenon to measure the current passing through the internally fused input pins of the IC. This allows the series resistance to stay very low. Current flow through the input rails of the IC generates a magnetic field, causing the Hall effect on the current flow through the integrated sensor. The resulting voltage is further conditioned and offset by the internal sections of the ACS711 IC, and after the conditioning, it appears at the output of the VIOUT pin.
The output voltage changes linearly with the input current, in steps of 110mV/A. To allow conversion via the external ADC, the output voltage is passed through the buffering circuit, comprised of the LM358 - a low noise operational amplifier in a unity gain configuration. The output of this buffer network is connected to the AN pin of the mikroBUS™ allowing an external AD conversion, or utilizing the output voltage in some other way. The response time of the output voltage is very short - in a magnitude of microseconds.
The output voltage is also routed to the MCP3221, a 12 Bit SAR type ADC with the I2C interface, from Microchip. This ADC is used in several different Click board™ designs, as it yields accurate conversions, it requires a low count of external components, and has a reasonably good signal to noise ratio (SNR). It can achieve up to 22.3ksps, which allows good measurement resolution for the most purposes. After the ACS711 output voltage has been converted to a digital value, it can be read via the I2C bus of the MCP3221 ADC. The I2C bus lines are routed to the respective I2C lines of the mikroBUS™ (SCL - clock; SDA - data). The provided library contains functions for simplified reading of the conversion values.
The FAULT pin indicates an overcurrent condition. If the measured current exceeds the specified range, this pin will be latched to a LOW logic level. This pin has a very fast response of only 1.3 µs, allowing it to be used a part of the overcurrent protection circuit. Naturally, it can be used as the interrupt pin, triggering an interrupt request on a host MCU. For this reason, it is routed to the INT pin of the mikroBUS™.
However, once latched, the ACS711 IC requires power cycling for the FAULT pin to be released. This can be done by pulling the RST pin of the mikroBUS™ to a HIGH logic level. This will cut the power through the PNP BJT. Pulling the RST pin to a LOW logic level will allow current flow through the BJT once again, and thus the ACS711 will release the FAULT pin. For the normal operation, RST pin should stay at the LOW logic level.
The onboard SMD jumper allows selection between 3.3V and 5V. This allows both 3.3V and 5V MCUs to communicate with the Hall current 2 Click.
The ACS711 IC offers a galvanic isolation for up to 100V. A care should be taken when operating with high voltages, not to touch the Click board™.
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