The DC/DC boost converter is a practical, almost ubiquitous component for stepping up voltage to meet the output requirements of a broad range of electronic applications. However, it can be inefficient and inflexible when product designers need leeway in dynamically adjusting output.
That’s a need that Analog Devices, Inc. (ADI), says it can fill with a controller that is versatile and efficient, adapting gracefully with reliable performance amid transitions to varying power sources.
ADI’s LT8277 Multi-Phase Boost Controller is a 2-phase constant frequency, current mode boost controller. It is designed to drive N-channel power MOSFETs with an interleaved operation that reduces system filtering capacitance needs. Its architecture provides stable operation across variable supply and output voltages. It can also be configured as a single-ended primary-inductor converter (SEPIC), delivering non-inverted output to adapt smoothly to varying power sources and changing conditions.
Boost converters convert a lower input voltage to a higher output voltage. They’re in widespread use in industrial and general applications. Common use cases include extending battery life, optimizing energy transfer in automobiles, and providing consistent power to LED lighting. They are typically used in low-voltage applications.
The LT8277 features a serial peripheral interface (SPI ) that can be used to adjust the output voltage (Vout) programmatically. This allows the voltage to be dynamically set to match system requirements or external conditions and provides design flexibility that is valuable in diverse applications, especially when precise voltage regulation is required. The LT8277 can also run without SPI, providing either a 36 V or a 60 V fixed output voltage.
The ADI controller also incorporates spread spectrum frequency modulation (SSFM) to reduce electromagnetic interference (EMI) in applications where compliance with stringent standards is a critical design requirement. Minimizing EMI prevents interference with other components or communication systems, and SSFM can modulate energy across a wider frequency range to reduce peak emissions at specific frequencies.
Another distinguishing factor is the ability to parallel multiple LT8277 devices that can be interleaved with up to eight phases. By distributing load current across multiple channels, designers can reduce current stress on any individual device.
Flexible and adaptable
ADI’S LT8277 provides a broad range of voltage selection and frequencies for customizing it to meet application requirements. Engineers can take advantage of a wide range of voltage and power levels with a minimum of off-chip components.
Its output can be tailored from 9 to 60 V, which can be set through the SPI. A write-only SPI interface utilizes a single, 12-bit shift register, with bits for setting output voltage, toggling phase 2 dropout, and configuring the clock output pin.
Operating frequencies can be set across 100 kHz to 2 MHz, either with an external resistor or synchronized to an external clock for precise timing by means of the SYNC pin.
These controls make the LT8277 adaptable for the design of numerous power supplies, tailoring its voltage precisely to the needs of an application, and fine-tuning its frequency to ensure optimal performance and EMI reduction.
As a step-up DC/DC controller, an LT8277 controls two power stages operated 180° out of phase from each other, and up to four devices can operate together to enable 4 or 8-phase configurations, with each phase operating in parallel to share the load and reduce stress on individual components. Use of multiple power devices can aid thermal management and reduce EMI.
The LT8277 operates in a 2-phase interleaved manner, reducing the overall ripple of its input and output to improve efficiency, minimize the size of input and output capacitors, and share the load evenly. This minimizes battery losses during boost conversion, enabling a stable voltage supply for applications such as lighting and infotainment systems.
Evaluating the LT8277 for applications
ADI’s EVAL-LT8277-AZ evaluation board (Figure 1) provides a development platform to explore and tailor applications using the LT8277 controller. Multiple EVAL-LT8277-AZ boards can be connected in parallel to enhance the overall power capability of a system design.
Figure 1: ADI’s evaluation board for the LT8277. (Image source: Analog Devices, Inc.)
The evaluation board can be used to assess the LT8277’s capabilities, including using the SPI interface for configuration and control, synchronizing frequencies in multi-phase systems, generating clock signals for 4 or 8-phase operation, and adjusting various parameters.
The evaluation board can be connected to ADI’s DC2026C Linduino One demonstration board to utilize an intuitive GUI for configuring LT8277 parameters.
Conclusion
The ADI LT8277 is a versatile and highly configurable controller with multi-phase boost and SEPIC capabilities that are well-suited for developing high-power and wide-input-range applications that require precise control and protection. Its support for frequency synchronization and phase interleaving can reduce input and output ripple, improve efficiency, and simplify thermal management.
By: Pete Bartolik
