ROHM Co., Ltd.

ROHM High-Performance Switching Regulator Controllers Compatible with FPGA Power Supply Requirements -- The first components from a Japanese manufacturer adopted into the power supply module for Xilinx's FPGA evaluation kit

Blog post   •   Aug 04, 2015 14:00 GMT

ROHM has recently announced that its power supply module has been selected for use with Xilinx's 7 Series FPGAs and in its Zynq ®-7000 All Programmable SoC evaluation kit.

This power supply module, designed completely in-house, employs 2 types of ROHM switching regulator controller ICs: BD95601MUV (x1) and BD95602MUV (x6). Although Avnet has sold a number of Xilinx FPGA evaluation kits, this marks the first time a power supply module has been adopted from a Japanese manufacturer.

These ICs, which serve as reference designs, are available as separate units as well. Here, we take a closer look at the characteristics and key technologies of ROHM's high-performance, versatile switching regulator controller ICs, ideal for not only FPGAs but for a wide range of other applications as well.

ROHM's power supply module used for Xilinx's 7 Series FPGAs and Zynq ®-7000 All Programmable SoC evaluation kit. It is sold by Avnet as a power supply module for mounting on baseboards (see photo at bottom left). Click here for details.


FPGA Power Supply Requirements

Today's high-end FPGA require advanced power supply management due to continued process refinement accompanied by lower voltages, power supply separation of the core and interface sections, and use of multiple power sources, for example mixed-signal digital and analog circuits. Requirements include not only voltage accuracy but also low ripple voltage, input sequence management, and high load transient response characteristics. The illustration at below shows the output configuration of ROHM's power supply module, with part numbers for each of the switching regulator controllers that form it.

Specifications for this Mini-Module Plus power supply are available through Avnet's Design Resource Center, and can be obtained by clicking on the 'Support Files & Downloads' button. Please note that user registration is required to access the specifications.


ROHM's power supply module output configuration and FPGA power supply requirements


ROHM's DC/DC converters achieve high accuracy and superior stability at low voltages and high output currents

Two types of switching regulator controller ICs are used in this power supply module, the 1ch BD95601MUV and the 2ch BD95602MUV, with characteristics as follows.


Optimal specifications and features for FPGA

  • H 3RegTM DC/DC controller provides high-speed transient response
  • Ultra-high 95%+ efficiency
  • Select between light load and continuous PWM modes. (Quiet light load mode: BD95602)
  • Adjustable soft start reduces inrush current during startup
  • Power Good output
  • Multiple protective functions: OCP (Over Current Protection), short circuit protection, TSD (Thermal Shut Down) temperature protection, UVLO (Undervoltage Lockout)


Basically, both products include high efficiency synchronous rectification buck controllers and feature light load mode that improves efficiency during light loads. In addition, the reference voltage (0.75V/0.7V) supports low voltage operation and the ±1% accuracy exceeds the ±3% requirement shown above, with low ripple voltage as well. The products also provide high-speed transient response through ROHM's proprietary H 3Reg control mode. These specifications make them ideal for FPGA power supply applications.


ROHM's original H 3Reg high-speed transient response control mode

One solution for speeding up load transient response is to use fixed on-time control. H 3Reg represents an advanced (improved) fixed on-time control system that further accelerates transient response during sudden load changes.

  • The output voltage (which is divided in order to compare with the reference voltage (REF) of the internal voltage control comparator input) is fed back to the FB pin.
  • During normal operation when the H 3Reg controller detects an FB pin voltage lower than the REF voltage, it turns on HG (high-side transistor) for a period of time (t ON) determined from the equation shown below, increasing the output voltage.

  • After 't ON' ends and HG turns off, LG is turned on (low side transistor), the FB pin voltage begins to drop, and LG is turned off when it reaches the same level as the REF voltage.
  • Repeating this process maintains constant output.
  • When the load suddenly changes, if the output drops and the FB pin voltage does not rise above the REF voltage even after the predetermined 't ON' time has elapsed, 't ON' is extended and additional power is supplied, accelerating the return of the output voltage. In other words, transient response is improved.
  • Once the output voltage is restored, normal operation is resumed.


The H 3Reg controller extends 't ON' when the FB (output) drops significantly due to load transients, hastening output recovery. 


Actual transient response of BD95602MUV. It is evident that the output, which has dropped in response to load transients from 0A to 8A, is returned at high speed.


Achieving a superior power supply

The photo at below shows the 1.2V output waveform of one of ROHM's power supply modules. At this output the ripple voltage is 5.6mV, which is less than 0.5%, highlighting the voltage accuracy of the BD95601MUV (this is the most objective description possible, since voltage deviation is not listed in the data sheet). Of course, while all factors have been adjusted and optimized as much as possible, it should be emphasized that superior results cannot be achieved regardless of the amount of adjustment unless the IC has inherently good characteristics.

Unfortunately, the design of switching power supplies is no easy task. The complicated process entails not only the calculation of component values, but also consideration of component chemistry to obtain optimum properties, baseboard design, and debugging in order to achieve the best performance possible.

Therefore, to obtain a superior power supply, one possible approach is to use this power supply module as is, then employ this reference design when transitioning to the actual device once FPGA kit evaluation is finished. However, there are a few cases where onboard power supply design is carried out independently. ROHM provides a comprehensive support system that leverages extensive expertise in component selection and baseboard design to help customers achieve optimum performance and reliability. Naturally, while IC selection is important, design support is also an essential element for users.

1.2V output from the ROHM's power supply module for Xilinx's FPGA kit. Vertical axis = 20mV/div. Ripple voltage is only 5.6mV at 1.2V.


Summary

The power supply specifications required for FPGA are as outlined above. In practice, when using FMC with a connector the wiring will become longer, making it even more difficult to achieve the target properties. The ability to deliver a module that satisfies the power supply requirements of high-end FPGAs such as the 7 Series is a testament to ROHM's superior power supply ICs and advanced expertise in power supply design.

And the fact that the reference design is from ROHM, a Japanese manufacturer, represents a major achievement that has special significance for our customers. As a Japanese manufacturer ROHM can provide superior levels of quality, reliability, supply, support, and communication - along with a range of discrete and other electronic components in addition to ICs - providing a distinct advantage.


Related Materials

BD95601MUV-LB(1ch) Product Information

BD95601MUV-LB(1ch) Datasheet

BD95602MUV(2ch) Product Information

BD95602MUV(2ch) Datasheet