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Industry Top-Class DC-DC Converter Enabling 80V and High EfficiencyHigh Voltages Alone Do Not Resolve User Problems


-Well then, I’d like to ask more specific equations about the BD9G341AEFJ. Could you please begin with a summary.

The MOSFET within the BD9G341AEFJ is an N-channel device rated at 80 V/3.5 A. The IC conversion method is a voltage step-down method known as diode rectification or asynchronous rectification. Using only a few external components such as resistors and capacitors, a Schottky barrier diode and an inductor, a high-performance, high-voltage DC-DC converter can easily be configured.

This device employs current mode control, so that phase compensation is simple and fast transient response is obtained. The switching frequency can be set in the range of 50 kHz to 750 kHz, so that size and efficiency can be optimized. Nearly all the protective functions used in the DC-DC converters of recent years are included.

I have prepared the features, main specifications, and an application circuit example for the device; please have a look.

  • ・Integrated 80 V/3.5 A rating and Ron
     150 mΩ Nch MOSFET
  • ・Maximum output current: 3A
  • ・Input voltage range: 12V to 76V
  • ・Output voltage range: 1.0V to input voltage
  • ・Switching frequency (adjustable):50kHz~
  • ・Reference voltage:1.0V±1.5%(25℃)±2%
     (over temperature)
  • ・Precision EN threshold ±3%
  • ・Soft-start function
  • ・Standby function
  • ・Over current protection(OCP),
     Under voltage lockout(UVLO),
     Thermal shutdown(TSD),
     and Over voltage protection(OVP) provided
  • ・Operating temperature: -40℃ to +85℃
  • ・Package: HTSOP-J8 (4.9 mm x 6.0 mm x
     1.0 mm)

-It seemed to me that the high voltage must make this a special product in some way, but the configuration is quite simple.

In general, high-voltage DC-DC converters frequently achieve a high voltage by using a circuit configuration that includes an external high-voltage MOSFET, but by incorporating a MOSFET, the BD9G341AEFJ eliminates the need to select a MOSFET. The footprint is thus reduced to the extent that there is no external MOSFET. In addition to the high voltage, this IC offers a full set of the features and functions required of a leading-edge DC-DC converter IC.

-So the IC includes other features and functions in addition to the high rated voltage.

The BD9G341AEFJ was developed placing emphasis on the following four main areas:

1.Achieving an industry top-level high voltage rating of 80 V
2.Attaining the highest efficiency in the industry for an 80 V-class DC-DC converter device
3.Boosting equipment reliability through protection functions to prevent breakdown and improve
4.Reducing footprint and simplifying design through a compact package and reduced number of
   external components

-And achieving a high voltage rating of 80V using an internal MOSFET was a challenge?

As explained at the beginning, the high voltage rating of 80V was achieved using ROHM’s industry-leading 0.6 μm BiCDMOS power process. The 80V products could not be manufactured without this advanced process; this is also clear from the fact that high-voltage products on the market do not extend to the 80 V level. And a voltage rating of 80 V is necessary to be able to reliably support the 48V input voltages that are common in the telecom and industry fields. 80 V can provide a sufficient margin to protect from sudden surges and the like, so that reliability can be further improved in applications where power supply conditions are exacting and high availability is required.

-Where efficiency is concerned, I have heard that efficiency is worse when stepping down from a high input voltage to a low voltage?

In general, because of device characteristics, the circuit configuration and other matters, the efficiency of DC-DC converters with high rated voltages tend to be inferior to those of converters with lower voltage ratings. Moreover, under conditions of a higher step-down ratio, such as from 48 V to 5 V, efficiency is poorer than when stepping down from 12 V to 5 V, for instance. Compared with similar ICs, the BD9G341AEFJ is capable of improving efficiency by up to a maximum 19%, and by 1.5% in the steady state. The graph presents data for an oscillation frequency of 300 kHz, an input voltage of 48 V and an output voltage of 5 V.


-Breakdown prevention and safety improvements are important when handling high voltages.

It is assumed that high voltages are being handled, and so protection functions that afford more safety will be necessary, and for protection from output short-circuits, an original “hiccup” method has been employed. In typical output short-circuit protection, the protection function operates, but an overheated state results, possibly culminating in device breakdown. The protection function of the BD9G341AEFJ periodically performs shutdown and restart, suppressing heat generation, and operation is restarted automatically when the fault has been removed. Through this method, breakdown of the power supply is prevented and the reliability of the application can be improved.


-The fourth area is miniaturization and simplification of design; these are goals that in recent times have become essential.

In addition to MOSFETs with a high voltage rating of 80 V, boost diodes for gate drives and other components that are normally external are being incorporated into ICs wherever possible to minimize the number of external components. Similar products use about 17 external components, but the BD9G341AEFJ requires only twelve. Moreover, the chip integration level has been increased, but the chip was successfully accommodated in a compact 8-pin HTSOP-J8 (4.9 x 6.0 x 1.0 mm) package. As a result, the footprint was reduced, and both design and evaluation were made extremely simple. In particular, because the MOSFET is internalized, the MOSFET selection and evaluation tasks are greatly alleviated, and the time to market can be shortened.


-Please give us a final summary.

When considering the requirements of the telecom and industrial equipment markets, it has been difficult to construct power supplies with sufficient margins using existing high-voltage DC-DC converter ICs. It was under these circumstances that ROHM entered the market for high-voltage DC-DC converter ICs on the strength of a new IC boasting a rated voltage of 80 V, putting it in the top tier of the industry. With this, user options for high-voltage DC-DC converter ICs can be said to have expanded.

However, it is essential that the demands of recent years for reduced power consumption and shortened time to market be addressed as well. The BD9G341AEFJ was developed on the understanding that merely raising the rated voltage to 80 V would not be sufficient to resolve user dissatisfaction and other problems.

At present we are developing derivative products to expand our lineup of high-voltage DC-DC converter products, so please expect further expansion of our product line.

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Downloadable materials, including lecture materials from ROHM-sponsored seminars and a selection guide for DC-DC converters, are now available.

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