Banebrydende PMBus power supply monitor og controller
Linear Technology introducerer LTC2978, der er power supply monitor og controller til digital management af op til otte 0V til 6V forsyninger (in english).
Today’s networking equipment is constantly being pushed to increase data throughput and performance, while keeping overall power consumption to a minimum. These systems require many ASICs, DSPs and processors with multiple voltage rails. Line cards with 30 to 40 rail voltages are not uncommon, but have not traditionally been simple to manage.
Users need to be able to easily adjust supply voltages, while reading parameters like voltage, current or temperature via an accessible interface. As a result, integrated power management solutions are sought in an effort to reduce system component count and complexity, which ultimately lead to lower cost, higher reliability and increased flexibility.
Linear Technology's new LTC2978 follows this theme and is one of the most integrated solutions the company has to offer in the System Monitor and Control product family to date.
The LTC2978 digital power manager offers accurate fault monitoring thresholds and adjustments, along with a wide array of supervisory features. The PMBus and LTPowerPlay GUI accesses an onboard EEPROM where user settings, measurements and faults are stored, and later interrogated for diagnostic purposes.
With just two connections, the LTC2978 can be cascaded for systems that monitor more than eight supply voltages. A multitude of built-in functions makes the LTC2978 a convenient all-in-one solution for CPUs, FPGAs or ASICs that require uncompromised sequencing and monitoring over multiple voltage rails.
Where it fits – Digital Power
Digital Power has been an emerging technology that has been stealing the spotlight in Power Electronics for the past couple of years. Controlling the power system digitally provides the opportunity to build-in more precise protection, diagnostic and monitoring mechanisms that were otherwise difficult and costly to implement in a purely analog power supply system.
Digitally controlling a power supply is radically different from switched-mode designs, slightly changing the concept and mindset needed to implement a digital power system. Designing digital controllers into systems calls for a different skill set from the engineer, including comfort with DSP algorithms, embedded microprocessor design and potential programming in a number of different languages.
Although digital power clearly has its benefits, implementing digital power is usually a very time-consuming and challenging design task. A digital power management IC that that can be easily designed in by new and experienced users alike is long overdue. Linear Technology answers this call by providing the very accessible LTC2978.
Features & Benefits
The LTC2978 is the first PMBus Power Supply Monitor and Controller on the market. Whereas the older SMBus specification was designed for battery management applications, PMBus allows new power technologies like digital power to flourish, facilitating communications between power converters, power management devices and system host processors.
The LTC2978 communicates with PMBus compliant devices at up to 400kHz, supporting over 75 standard command functions, as well as proprietary commands that provide innovative value-added features. Firmware development and writing code is drastically minimized thanks to intuitive GUI-based software that was specifically designed for the LTC2978.
The LTC2978 is equipped with all of the necessary functions to address today’s most demanding multi-rail digital power management systems. An 8-channel sequencer allows synchronization of sequencing delays when turning ON or OFF supplies in any order. If there is a need to support more channels and dependencies must be established, multiple LTC2978’s can be strung together with just one connection and a fault-sharing bus can be used; up to 72 supplies per I2C segment of a bus can be managed.
High-speed comparators supervise the voltage level of each rail and take immediate action if a rail goes out of its specified limits. Margining and trimming each rail is extremely accurate over temperature, even at low voltages, using a digital servo loop that measures the rail voltage and continuously curtails any inaccuracies.
The LTC2978 also boasts a resolution of 12.5µV and an accuracy of 0.25% when monitoring voltage and current. The LTC2978 performs all of its functions without any intervention from a host processor for truly autonomous operation. Fault diagnosis is as simple as accessing the registers of EEPROM and examining the user settings and fault log.
Implementing the LTC2978 discretely would be a very unattractive proposal because of total cost, functionality, complexity and size. Eight 15-bit ΔΣ ADC, eight 10-bit voltage-buffered IDACs, eight 10-bit voltage supervisors, a 9:1 ADC MUX, a precise reference, an 8-channel sequencer and a PMBus interface would put the cost over $20.
This does not take into account the loss of secondary functions integrated in the LTC2978, including self temperature measurement, current sensing and memory capabilities. Furthermore, a multi-rail power system typically requires that these discrete devices controlled by an FPGA or microcontroller be sprinkled around the board which significantly complicates layout. The LTC2978 is offered in a RoHS-compliant 64-lead 9mm x 9mm package. As sophisticated as the LTC2978 sounds, it offers a simple and highly effective solution when compared to a discrete solution or other power management ICs offered today.
The LTC2978 is the next generation follow-on to the successful LTC2970, which released in 2006. The LTC2970 is a dual I2C power supply monitor and margining controller and was Linear Technology’s first product to venture into the digital power realm.
While the LTC2970 can also digitally control, margin and trim the output voltage of DC/DC converters, it does not incorporate the supervisory and sequencing functions found in the LTC2978. The LTC2978 is better in many respects; using higher accuracy components, adding more channels and adding more functionality, the LTC2978 expands on the definition of digital power, without complicating the device’s accessibility. The LTC2978 is a fully-featured part that integrates all possible functionality digital power users could ask for and gives them easy access to an otherwise daunting analog power system.
