Implementing Digital Power Management for Analog Power Supplies
By Shyam Chandra, Lattice Semiconductor Corporation
To meet market pressures, designers employ many of the latest high density ASICs, CPUs, FPGAs and memory ICs to increase the features on their circuit boards. Each of these ICs need multiple power supplies. The net result is an increase in the number of power supplies per board, and a corresponding increase in the complexity of power management.
Shyam Chandra, Lattice Semiconductor Corporation
By Shyam Chandra, Lattice Semiconductor Corporation
To meet market pressures, designers employ many of the latest high density ASICs, CPUs, FPGAs and memory ICs to increase the number of features on their circuit boards. Each of these ICs need multiple power supplies. The net result is an increase in the number of power supplies per board, and a corresponding increase in the complexity of power management.
Coupled with this increased complexity, some of the power management functions, such as sequencing and monitoring for supply faults, require tweaking during board debug. Traditional off-the-shelf, factory-set single function power management ICs do not provide the flexibility needed.The use of digital intelligence to manage on-board DC-DC Converters is called Digital Power Management.
The Power SIG and Z-Alliance consortia have proposed standard architectures for digital power management. Both these standards rely on a digital communication bus (PMBus, Z-Bus) between a central controller and individual DC-DC converters to provide a flexible power management solution.In order to be compliant with these standards, DC-DC converters should support the communication interface and the associated protocol command structures.
Designers typically determine the final power supply requirements of their boards after all the ICs on the board have been selected. In addition to identifying the type of DC-DC converters, the designer must determine the sequencing, monitoring, supervisory signal generation, trimming and margining of those DC-DC converters.
Presently, the majority of DC-DC converters in the market are analog and do not have the communications capability to take advantage of standardized digital power management solutions.Consequently, designs using analog DC-DC converters have to implement power management using off-the-shelf single function ICs.However, the Power Manager II IC family from Lattice Semiconductor provides the flexibility of digital power management while using traditional analog DC-DC converters, and at a lower overall cost than a solution using off-the-shelf single function ICs.
The following application example describes the use of a Power Manager II device to implement digital power management using analog DC-DC Converters in an ATCA carrier line card.
Digital Power Management Implementation
The diagram below shows multiple analog power supplies feeding power to the payload circuitry of an ATCA line card.
ATCA line cards typically use six to ten DC-DC converters on board. The Lattice Power Manager II (the digital power manager, or “DPM”) controls the sequencing of these supplies through the DC-DC converter enable pins, monitors the output voltage of these supplies for over-voltage and under-voltage faults and activates supervisory signals when a fault is detected. The DPM trims the output voltages of these DC-DC converters and also margins them using the trim/ feedback inputs of these supplies. The onboard microcontroller (Intelligent Platform Management Controller, or “IPMC”) instructs the DPM to turn supplies on/off or trim/ margin supplies. In addition, the DPM implements a 12V hot-swap function, using N-Channel MOSFETs that are used to feed 12V power to Advanced Mezzanine Cards (AMCs).
The Power Manager II device (DPM) provides a 48-macrocell CPLD, 24 precision programmable threshold comparators, 4 long duration programmable timers, 4 charge pumps, a 10-bit ADC, eight 8-bit DACs and I2C interface.
The power supply sequencing algorithm is implemented in the DPM’s on-chip 48-macrocell CPLD, and the open drain outputs control the standard on/off signal of the analog DC-DC converter. The output voltage fault level can be set by programming the comparator threshold value. The ADC and the I2C interface are used to measure the voltages. The DPM’s DAC can be used to set the DC-DC converter output voltage through the Trim/ Feedback pins of the analog DC-DC converters. The I2C interface also can be used to monitor the digital status or control the sequencing and monitoring algorithm implemented in the CPLD.
There is no need for any off-the-shelf single-function power management ICs, because all of these functions are integrated into the Power Manager II device. Using software, designers can tweak the supply sequencing or voltage monitoring thresholds during the debug process. Because the cost of the Power Manager II IC is less than the cost of off-the-shelf single function ICs, the solution is also less expensive.
The Power Manager II device, through its programmable monitoring and control features, is able to implement flexible, complex power management using any analog DC-DC converter. The advantages of a digital power management solution using the Power Manager II device include a reduced number of components, reduced development time, the flexibility to accommodate last minute changes to the algorithm, an increased number of DC-DC converter options for any given design, and low cost.
Srirama (“Shyam”) Chandra is the Product Marketing Manager for the in-system programmable mixed signal products at Lattice Semiconductor Corp. Prior to joining Lattice, Chandra worked for Vantis and AMD in sales and applications and previously was a telecom design engineer with Indian Telephone Industries. Chandra received his Masters degree in Electrical Engineering from the Indian Institute of Technology, Madras.
Chandra can be contacted at:
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