Technical Information｜Four Major Current Detection Design Trends Promoting the Development of Electrification

Of all the buzzwords describing the increasingly electrified world, one stands out: galvanic sensing. Familiar innovations in solar arrays, electric vehicle (EV) charging stations, or robotics would be nearly impossible to achieve if current-sensing technology was unreliable, inaccurate, and difficult to design into.

This article describes four major design trends emerging as electrification applications evolve, as well as current sensing technologies used to increase system voltage, enhance system protection, enable telemetry monitoring, and reduce form factor. Overall, current sensors monitor an important parameter in an electrical system, the current, which enables the system to operate as efficiently as possible within safe limits.

As efficiency requirements become more stringent, system voltages increase, helping to improve efficiency. According to Ohm's law, at a higher system voltage, the same amount of power can be obtained by reducing the load current, which helps reduce I2R losses in the system. At higher voltages, the system can deliver high power more efficiently because the current range is smaller and less heat is generated by the AC/DC or DC/DC power converter stages.

The electric vehicle charger shown in Figure 1 is disconnecting power from the grid, and its voltage level may be 120V AC , 240V AC , 230V AC (single phase) or 400V AC (three phase). A typical EV charger delivers AC power from the grid to an EV onboard charger, which converts the AC power to DC power and charges the battery.

In a DC fast charger, AC power is transmitted from the grid to the EV charger, where it is converted from AC to DC and provides up to 920V DC to the battery , thereby speeding up charging. Stepping up to a higher voltage level and maintaining a similar current level delivers more power directly to the battery, allowing for faster and more efficient charging.

Current sensors help improve the system efficiency of electric vehicle chargers and can be used in multiple locations throughout the system. These sensors can be used on the AC line input to monitor current flow and thus regulate the reactive power entering the front end of the system. On the other hand, this configuration can be used to monitor faults on the positive or negative node after the system power factor control loop and the second DC/DC stage.

Flux balancing can also be achieved using current sensing from a differential amplifier somewhere between the first DC/DC stage and the second DC/DC stage. In addition, it is necessary to use an isolated current sensor such as the AMCS1100 or TMCS1100 to provide protection for the system and the personnel operating the electric vehicle charger.

Electrification also increases the need for system protection to ensure rapid response to events outside the safe operating area and avoid damage to semiconductors and other sensitive devices. In most systems, some form of system protection ensures that the system operates as expected. For example, if the robot shown in Figure 2 picked up an unusually heavy item, the motors would experience noticeable current spikes.

A current spike may mean that the load is beyond the robot's capabilities, potentially damaging the system or components within the physical robot arm. Current-sensing devices with integrated comparators detect peak current inrush into the motor that may exceed the system's safe operating area. The INA301 with integrated overcurrent comparator can respond quickly (less than 1µS) and set an alarm, which can cause system shutdown. This is similar to point-of-load measurements, where shunt-based sensors such as the INA228 and INA226 ultra-precision bidirectional current-sense amplifiers can monitor the current and voltage levels through a specific node, ensuring that the node remains within its safe operating area.

As applications become more electrified, so do the requirements for monitoring to track energy consumption levels and improve predictive maintenance.

An example of monitoring or telemetry monitoring for predictive maintenance is data logging of the current and voltage levels of cooling fans in a rack-mounted server system. Devices such as the INA232 are used to record data on the fan's power consumption. Through data logging, the system can alert technicians that a fan may be operating erratically or is nearing the end of its useful life.

A digital power monitor is a suitable device for this type of use case because it receives both bus voltage and current information. Digital power monitor ICs use on-board computing to calculate power, charge, and energy and transmit this information (along with bus voltage and current data) through an I2C or serial peripheral interface. On-chip computing can reduce the number of processes on the CPU or microcontroller, so processing resources can be used more efficiently to handle other tasks. This is especially important for systems with task-intensive CPUs or microprocessors.

As more and more applications include more electronic components or need to be installed in smaller spaces, there is a greater need to reduce the size of components or increase the number of functions per unit, thereby helping to reduce the size of the overall circuit board. area. Many systems, such as smartphones and robotic systems, are subject to size constraints that require continuous reduction in size and increase in the number of features.

Smaller current sensing devices allow designers to increase monitoring of the entire system or reduce the overall size of the system. Both cases have certain advantages, depending on the overall system parameters. Reducing the size of integrated circuits (ICs) or increasing the number of functions per unit increases functional density, enabling powerful personal electronics, car chargers, and small collaborative robot motor drive systems.

Utilizing ultra-small ICs or feature-rich chips provides the basis for smaller systems. For example, chip packaging options such as the Wafer-Chip Scale Package (WCSP) or the INA253 with integrated shunts allow designers to reduce the size of their systems without compromising performance or functionality.

By better understanding the above trends and the ICs that help enable them, you can address specific high-voltage design challenges and achieve reliability and safety by monitoring current measurements to ensure the system is operating within a safe operating area.