June Birth Magoncia

user Electronics Engineer

city Innovuze Solutions, Inc.

  • Adjustable Electronic Circuit Protection

  • Created: Jun 09, 2016

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The INA301A2 is a device that is composed of a high common-mode current sensing amplifier and a high-speed comparator. It can be used to monitor the current consumption of a load and detect overcurrent condition. The device uses an external current sense resistor attached to its internal amplifier common-mode input to monitor the current consumption of a load powered by any single power supply that ranges from 0V up to 36V. The output of this current sensing amplifier serves as an input to the internal comparator that outputs a LOW signal if ever the output of the internal amplifier exceeds the threshold voltage set by an external limit resistor. The output of the current sensing amplifier and the comparator can be used as inputs to a microcontroller for a specific function.

In this reference design, the outputs of the INA301A2 device are transmitted to the ATmega328P-PU microcontroller to create an adjustable electronic circuit protection. This electronic circuit protection uses a relay to switch ON and OFF the 220VAC main line of the load’s power supply. The INA301A2 senses the current drawn by the load through the current sense resistor R6. The voltage drop across R6 is multiplied to 50 (gain of the internal amplifier) and sent to the microcontroller through the OUT pin of the INA301A2. If the current drawn by the load exceeds the current limit set by the DIP switch S2 to the microcontroller, the relay disconnects the 220VAC main line of the load’s power supply to protect the whole system from overcurrent. The current limit of this electronic circuit protection can be adjusted through the three-position DIP switch S2. The principle of setting the switch is just like in a binary to decimal conversion. Since there are three switches inside S2, the user can assign eight different current limits by programming the ATmega328P-PU microcontroller. The maximum current limit allowed by the INA301A2 in this design is just up to 10A since the resistance of the external limit resistor used R5 is 62kΩ. The resistance of R5 sets the threshold voltage or trip voltage of the INA301A2 device. If the output of the internal amplifier exceeds the threshold voltage set by R5, the /ALERT pin of the INA301A2 will pull the PB2 pin of ATmega328P-PU to ground. The ATmega328P-PU must also be programmed to turn OFF the relay if its PB2 pin is pulled to ground by the /ALERT pin of INA301A2. In this case, even if the 10A maximum current limit is not included in the eight different current limits set by the DIP switch S2 and in the microcontroller’s program, the relay will still turn OFF at that maximum level.

The INA301A2 device has two modes of reset operation, latch mode and transparent mode. If the RESET pin of the device is set to HIGH, the device operates in latch mode, while if the RESET pin is set to LOW or grounded; the device is in transparent mode. The reset mode of the device affects the behavior of the /ALERT pin after the voltage drop across the current sense resistor R6 drops below the threshold voltage of the internal comparator. If the device is in latch mode, the /ALERT pin never goes back to HIGH state unless the RESET pin is pulled low for at least 100ns. In this design, the INA301A2 is set into transparent mode since the RESET pin is grounded. In transparent mode, the /ALERT pin automatically returns to HIGH state if the voltage across R6 drops below the threshold voltage. In this way, there is no need to apply a LOW signal on the RESET pin to reset the INA301A2 device. The switching part of this project which includes the relay, operates in 12V, while the INA301A2 and the ATmega328P-PU operates in 5V. This adjustable electronic circuit protection can be used in any system that has a power supply not exceeding 36V and consumes less than 10A of current.