Using PassThru technology helps extend the lifespan of energy storage systems

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PassThru™ mode is a controller operating mode that allows the power source to be directly connected to the load. PassThru mode is used in buck-boost or boost converters and can improve operational efficiency and electromagnetic compatibility. This article will introduce you to the advantages of controllers using PassThru technology and how PassThru mode can extend the lifespan of energy storage systems, especially the total operating time of supercapacitor. Additionally, it will present the product features of the ADI LT8210.

Methods to extend battery life and enhance energy storage system performance

Batteries are the crucial components of energy storage systems. Extending battery life means stronger system performance, longer operational time, and lower costs. Typically, there are three ways to prolong battery life, including improving battery technology, designing better devices, and providing innovative energy management systems.

Improving battery technology involves selecting suitable batteries for specific applications and designing appropriate battery management systems to control charging, regulate temperature, and minimize power consumption. Designing better devices require considering efficient hardware components and robust firmware, both of which are essential for balancing functionality and lifespan indicators. To achieve energy optimization intelligently, the latest power management systems can be utilized. These systems employ AI-based algorithms, novel topology structures, and efficient converter control methods, such as PassThru mode and power-saving mode.

In addition, utilizing energy storage devices such as supercapacitors alongside batteries can benefit various application scenarios. Supercapacitors offer advantages including support for quick charging and discharging of short-term burst of power, longer lifetime, and higher overall system efficiency. For instance, supercapacitors are well-suited for quickly energy storage and providing backup power. They can withstand extreme temperature conditions. When used in combined with batteries, such as in electric vehicles, supercapacitors help improve performance and extend battery life. Additionally, supercapacitors are more environmentally friendly.

One key difference between supercapacitors and batteries is that, at the same rated voltage, a 6-cell 0.1Ah lithium polymer battery exhibits the characteristics of a voltage source, providing a more stable voltage throughout the operation. In contrast, when current flows from a 2F supercapacitor to the load, the voltage linearly decreases. The linear discharge characteristic of supercapacitors requires a more efficient system to convert their energy. In this scenario, it is more suitable to use a buck-boost converter function, as this converter can appropriately adjust and regulate output voltage stability regardless of whether the input voltage is lower or higher than the set output voltage.

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PassThru mode is an important means to achieve efficiency optimization

PassThru technology is a fundamental feature of wide-input power devices. Compared to systems using conventional control methods (standard buck-boost controller), it can improve efficiency and extend the lifespan of energy storage systems. "Pass-through" refers to the direct transmission of input within a predefined voltage window to the output, as if a shorted wire occurred. PassThru technology acts as a network between the power source (e.g., supercapacitor) and the load, ensuring voltage regulation within specified acceptable ranges. It provides a direct path from the power source to the load to ensure that the device operates as efficiently as possible. PassThru mode is an important means to ensure optimized efficiency for devices powered by supercapacitors because it reduces the load/unload cycles of supercapacitors and improves the device's EMI and overall performance.

In a four-switch buck-boost converter, PassThru mode provides a direct path from the power source to the output load based on specified window settings. The input is directly passed to the output, eliminating switching losses, thus improving efficiency within the specified PassThru window. Additionally, it enhances electromagnetic compatibility since there is no switching frequency during PassThru mode. PassThru mode in buck-boost converters offers flexibility by allowing different output voltages for the buck output compared to the boost output. This is contrary to typical buck-boost ICs that provide only one nominal output voltage. This feature also protects the load when input voltage behaves abnormally.

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PassThru mode control improves system operating efficiency

PassThru Mode is a working mode of the LT8210, which is the only buck-boost controller IC on the market with this capability. Using the DC2814A-A demo board as an example, this demo board employs the LT8210 with an input voltage range of 4 V to 40 V, a full load current of 3 A, and an output voltage of 8 V to 16 V. When operating in PassThru Mode, efficiency can be improved by up to 5% under heavier loads compared to buck-boost operation, and by up to 17% under lighter loads (such as a 10% current load). Therefore, PassThru Mode achieves significant performance enhancements under light load operating conditions.

It is worth noting that although the PassThru mode of the LT8210 allows for an output voltage different from the buck output voltage, there is still a buck-boost region when the input voltage is near the output voltage setting. The reason for this buck-boost region in the LT8210 is that there is an overlap between the inductor current regulation buck and boost control regions.

To assess the application effectiveness of PassThru mode, a four-switch buck-boost converter is used as a pre-regulator for point-of-load converter, which is also used as a motor driver. Although the power source is a 24V supercapacitor, the DC motor requires a 9V input voltage and 0.3A input current. The buck-boost converter will operate in PassThru mode, or in the conventional four-switch buck-boost controller running in Continuous Conduction Mode (CCM). Note that the conventional buck-boost control does not have PassThru mode; it only has buck, boost, and buck-boost operations.

The system using PassThru mode sets its boost output voltage to 12V and its buck output voltage to 27V. This way, the startup voltage of the supercapacitor can be within the passband limit. Therefore, the system will go through PassThru mode from the 24V to 12V supercapacitor voltage. During this period, the efficiency reaches 99.9%. Compared to the conventional control method system, PassThru mode improves efficiency by 22% to 27%.

Some of the key reasons for the higher efficiency of systems controlled by PassThru mode include the elimination of the buck operation, ensuring that the battery voltage remains within the recommended passband, and its design to operate under light loads, focusing on reducing switch losses. PassThru technology is a critical means of optimizing performance for devices powered by supercapacitors. Compared to conventional systems controlled by CCM (Continuous Conduction Mode) buck-boost operation, adopting the LT8210 synchronous buck-boost controller with PassThru mode can significantly enhance the efficiency of devices powered by supercapacitors.

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Supports synchronous 4-switch buck-boost DC/DC controllers

ADI introduced the LT8210, a 100V VIN and VOUT synchronous 4-switch buck-boost DC/DC controller with pass-thru capability. It operates in PassThru, forced continuous, pulse-skipping, and Burst® mode. In PassThru mode, when the input voltage is within the user-programmable window, the input is directly passed through to the output. PassThru mode eliminates switching losses and EMI, while maximizing efficiency. For input voltages above or below the pass-thru window, the buck or boost regulation loop respectively maintains the output at the set maximum or minimum values.

The GATEVCC driver of the LT8210 is regulated to 10.6V to enable the use of standard-level MOSFETs and can be powered through the EXTVCC pin to enhance efficiency. The GATEVCC regulator features back-drive protection, which maintains regulation in case of input voltage brownouts. By adding a single N-channel MOSFET, optional reverse input protection down to -40V can be achieved. The LT8210 also includes a precision current-sensing amplifier, allowing for accurate monitoring and limitation of output or input average current.

The LT8210 features Pin-Selectable PassThru or fixed-output CCM, DCM, Burst® operating modes, and programmable non-switching PassThru window. It has an 18μA PassThru mode IQ with 99.9% efficiency, VIN range from 2.8V to 100V (4.5V at startup), VOUT range from 1V to 100V, reverse input protection up to -40V, ±1.25% output voltage accuracy (-40°C to 125°C), and ±3% accurate current monitoring, ±5% accurate current regulation. It supports 10V quad N-channel MOSFET gate drivers, and EXTVCC LDO can be powered from VOUT/external power rails. It has ±20% cycle-by-cycle inductor current limit, no top MOSFET refresh noise in buck or boost modes, fixed/phase-lockable frequency from 80kHz to 400kHz, suitable for low-EMI spread spectrum frequency modulation (SSFM). It features a power good output voltage/overcurrent monitor and is available in 38-lead TSSOP and 40-lead (6mm x 6mm) QFN packages. The LT8210 can be applied in automotive, industrial, telecom, avionics systems, automotive start-stop systems, emergency call applications, and applications compliant with ISO 7637, ISO 16750, MIL-1275, DO-160.

LT8210 also offers several evaluation kits, including the DC2814A-B demo board, which is a high voltage, high efficiency synchronous buck-boost DC/DC converter with an input voltage range of 9V to 80V, capable of delivering a maximum load current of 2.5A, and featuring an output range of 24V to 34V. Another demonstration circuit, the DC2814A-C, has an input voltage range of 26V to 80V, providing a maximum load current of 2A, with an output range of 36V to 56V. Additionally, the DC2814A-A demo circuit has an input voltage range of 8V to 80V, which can run down to 3.5V after device startup, offering a maximum load current of 3A, and featuring an output range of 8V to 16V.

These demo boards all incorporate the LT8210EUJ controller, utilizing a constant frequency current mode architecture allowing for a phase-lockable frequency of up to 400kHz, while optional input or output current feedback loops provide support for battery charging and other applications. Additionally, ADI offers LTspice®, a powerful and efficient free simulation software, schematic capture, and waveform viewer, enhancing capabilities and models for improving the simulation of analog circuits.

Conclusion

The LT8210, a 4-switch synchronous buck-boost DC/DC controller introduced by ADI, operates in PassThru, forced continuous, pulse-skipping, and Burst® modes, significantly optimizing the efficiency of supercapacitor-powered devices. This buck-boost DC/DC controller, which supports PassThru technology, will enhance battery efficiency and prolong the lifespan of energy storage systems, making it an ideal companion for applications such as automotive, industrial, telecom, and aerospace electronic systems.

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