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Switching Regulator Controllers Compatible with FPGA Power Supply Requirements

"H3Reg", a Key Technology for Fast Transient Response

Keyword
  • Low-voltage large-current
  • H3Reg
  • Load transient response
  • Advanced constant on-time control

The BD95601MUV and BD95602MUV are switching regulator controller ICs designed to support the low-voltage, large-current requirements of the recent power supplies. In addition to high efficiency and numerous protection functions, these ICs exhibit optimal performance as power supplies for FPGAs and CPUs, which require high voltage accuracy and stability.

Under the conditions of low voltages and large currents, fast load transient response is necessary in order to maintain voltage accuracy and ensure high stability. When the load current changes suddenly, the output voltage necessarily fluctuates momentarily. How rapidly the recovery from this fluctuation can be made depends on the load transient response characteristic.

Constant on-time control is known as a control method to achieve a fast load transient response characteristic. The BD95601MUV and BD95602MUV adopt ROHM's proprietary "H3Reg" control method. This is an advanced constant on-time control method that further increases the speed of the transient response characteristic of the constant on-time control method. "H3Reg" operation is explained below.

graf_0526_01

  • ・The divided output voltage is fed back to the FB pin
     for comparison with a reference voltage (REF) of an
     internal voltage control comparator input.
  • ・In normal operation, upon detecting that the voltage at
     the FB pint has dropped below the REF voltage, the
     H3Reg controller turns HG on (turns on the high-side
     transistor) during a time (tON) determined by the
     following equation, and causes the output voltage to
     rise.

graf_0526_01

  • ・When HG turns off after tON has elapsed, LG is turned
     on (the low-side transistor is turned on), the FB pin
     voltage begins to fall, and upon becoming equal to the
     REF voltage, LG is turned off.
  • ・By repeating this procedure, the output is maintained
     at a constant value.
  • ・Upon a sudden change in the load, the output falls, and
     if the FB pin voltage does not rise to the REF voltage or
     higher even after time tON has elapsed, the time tON is
     lengthened to provide more power, thus hastening
     recovery of the output voltage. That is, the transient
     response characteristic is improved.
  • ・When the output voltage has recovered, normal
     operation is resumed.

In a FPGA, CPU and the like, during a transition from a sleep state to full operation, such sudden fluctuations in load current occur. If the power supply voltage does not promptly recover with minimal fluctuations, operation of the FPGA or CPU may be affected. The lower the output voltage becomes, the smaller is the tolerance of fluctuations due to load transitions, and the larger the fluctuations in load current, the larger are the resulting voltage fluctuations. Hence low-voltage, large-current conditions are particularly demanding for power supplies, and the power supply performance must be able to meet such demands.

Switching Regulator Controllers Compatible with FPGA Power Supply Requirements

Power Supply Design Technical Materials Free Download

Power Supply Design Technical Materials Free Download

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