Introduction
The increasing demand for efficiency in power electronics necessitates the continuous search for the best possible solutions. Applications such as power supplies, motor control, renewable energy, and lighting technologies are typical examples in rapidly growing markets that require power semiconductors that maximize economic viability. This implies the highest efficiency in static operation as well as at increasingly higher switching frequencies. Conventional semiconductor structures, such as the planar construction of a power MOSFET, are often at their physical limits. Therefore, Renesas has developed a completely new line of power MOSFETs with a so-called Superjunction structure. This meets the requirements for both static and dynamic operation. Typical parameters for static and dynamic properties are RDSON (drain-source resistance in the conduction state) and QGD (gate-drain charge), respectively.
Fundamentals of Power Losses, Equations, and Parameters.
In a power MOSFET, the so-called RDSON greatly influences the losses.
Power losses of a power MOSFET in static mode.
During switching, the losses in the diode structure must be added together to calculate the total losses. This equation and its approximation are applied:
by exchanging the symbols “u, U” for “v, V”:
Diode Structure Losses:
The power in the controller stage can be considered a loss. The gate load QG greatly influences these losses. The calculation is performed as follows:
change to
Therefore, both RDSON and QG influence losses. The term "factor of merit" (FOM) combines both parameters through multiplication. This is a simple way to assess efficiency.
The symbol “QGD” is also used for the door-drain load.
1. Pton: turn-on, Switching losses, Switching on process.
Pton=1/6x ž1xV1xtw1xf, = 1/6x7.8Ax84Vx0.5usx48.8kHz,=2.66W.
2. Put, Statics loss.
Pon=ž22xRDS(on)(max)xaxtw2xf,=4A2x0.16Wx2.0x11.5usx48.8kHz,=2.87W
3. Ptoff: turn-off, Switching losses, Switching off process.
Ptoff=1/6x ž2xV2xtw3xf, = 1/6x4.0Ax54Vx0.3usx48.8kHz,=0.53W.
4. Ptotal, Total power losses.
Ptotal=Pton+Pon+Ptoff,=2.66W+2.60W+0.53W,=5.8W.
Renesas has developed a completely new line of superjunction power MOSFETs (SJ-PMOSFETs). Their 600V/650V voltage range, along with a current range of 6.1A to 55A, covers most consumer and industrial applications. The low RDSON and QG values achieved result in a FOM that provides an ideal basis for designing energy-efficient circuits. For the static loss range, this product line offers several advantages over conventional power MOSFET structures. At higher frequencies (> 50 kHz), SJ-PMOSFETs are significantly superior even to IGBTs in terms of total power losses.
Examples of Standard Packages:
SJ-PMOSFETs are typically built on an N+ substrate. The structure consists of multiple columns layered with P-doped material on a low-N-doped material. A multi-stage epitaxial growth process builds the columns layer by layer, increasing the overall thickness of the implanted layer until the required stress tolerance is achieved. This version of the process is shown below in Figure 1 (center). However, the drawback of this production process is the relatively slow epitaxial growth of column layers and its complexity due to the multiple repetitions of the steps.
Renesas has developed a new proprietary method for constructing superjoint structures that avoids the aforementioned drawbacks. Renesas applies the deep-trench technique, a production process that involves etching trenches into the low-doping N-type material to create P-type material regions. Figure 1 (right) illustrates the deep-trench structure. Thanks to a reliable production process, high-precision mask alignment and doping, along with the miniaturization of P-type material columns, very low RDSON values and extremely low internal capacitance are achieved, which in turn lead to low QG (QGD) values. This results in the best FOM values.
Figure 2 shows the cross-section of a deep-trench structure.
One member of the family is the RJK60S5DPK device, with absolute maximum ratings of 600V and 20A. It achieves excellent results in terms of static losses and switching properties. The specific resistance per unit area is approximately 52 percent lower than in conventional designs. Exceptionally low gate-drain load (GDL) values, around 80 percent lower than conventional designs, enable fast switching with minimal losses. Advantages for the user, compared to conventional designs, include low heat generation, allowing for compact circuit designs, the use of smaller packages, and the application of suitable heat sinks.
A derivative version of this device incorporates a fast recovery diode which, thanks to its faster switching speed, further reduces power losses during switching, thus minimizing heat generation (Figure 4).
Over the next few years, the SJ-PMOSFET family will be continuously expanded with additional current ranges and higher voltage versions. Furthermore, Renesas will offer optimized versions for specific application areas.
Application Example: Power Supply.
The power supply can be cited as an example of the growing demand for efficiency in an application.
The example shows the circuit topology (Figure 5) of a power supply with synchronous rectification. The topology includes a power factor correction (PFC) control and a half-bridge, both equipped with deep-groove SJ-PMOSFETs on the primary side. The secondary side incorporates medium-voltage power MOSFETs with 60V voltage tolerances. In addition to discrete components, Renesas also supplies other essential components such as the PFC IC and the ICs for synchronous rectification, optocouplers for galvanically isolated control signals, and a microcontroller for the overall controls.
The implemented SJ-PMOSFETs make a decisive contribution to increasing efficiency.
The diagram in Figure 6 shows the efficiency increase achieved with the "deep trench" SJ-PMOSFET presented here and is compared to a competitor's product with an epitaxial SJ structure.
Online support for product selection:
By restructuring and improving its support for cross-reference and parametric searches, Renesas has significantly simplified the product selection process. The added application support, which goes beyond simple device selection, offers considerable added value to the user.
The product selection support presented below can be accessed via a centralized website: http://www.renesas.eu/products/discrete/peerguide.jsp
The clear graphic design of a flowchart (Figure 7) helps in selecting the product. Starting with a planned application and a circuit topology to be developed, clicking on the appropriate field activates the desired function, such as cross-reference search, parametric search, or product overview.
The cross-reference website http://www.renesas.eu/req/other_product_search.do?event=otherProductSearch helps you find the closest equivalent Renesas device to a given competitor's device; several options are provided where appropriate. The most important parameters are displayed directly, and the complete data sheet can be downloaded instantly.
Cross-referencing is available not only for the new SJ-PMOSFET product series but for the entire product range.
For many products, especially SJ-PMOSFETs, SPICE parameters can also be downloaded so that the basic behavior of the device can be simulated even before samples are available.
Another tool for product selection is the parametric search tool, which can be accessed through this website:
http://www.renesas.eu/req/parametric_search.do?prdCategoryKey=12&selectedConList=®ion=
Here, the search for desired products can be refined by entering or selecting parameters by clicking or moving the cursor. The corresponding product list is then displayed.
Another very practical feature of this tool is the ability to export the list of proposals to an Excel spreadsheet for further processing.
Another product selection tool uses the application to be developed and its topology as a starting point, rather than product characteristics. This practical approach allows the developer to gain an overview of the devices proposed for the circuit topologies to be developed.
Online simulation support
In addition to the possibility of analyzing the basic suitability of the SJ-PMOSFET in the circuit with the help of SPICE parameters on our own computer, Renesas also offers a complete simulation environment called “Powere SIM” on its website.
This tool is offered free of charge to the user. For example, starting with the topology and components of the selected circuit, you can simulate signal waveforms, frequency response, thermal behavior, efficiency, and more. This simulation environment is continuously being improved and offers an ideal platform for users to significantly accelerate the development process with minimal effort.
Summary:
With its new series of superjunction power MOSFETs (SJ-PMOSFETs) based on proprietary deep-trench technology, Renesas has set a new benchmark among high-efficiency power semiconductors. This enables a significant increase in application efficiency. The production process is entirely proprietary, ensuring consistently high product quality.
Renesas provides users with a comprehensive suite of functional online product selection tools, all centrally accessible via the website. Product selection based on the intended circuit topology is a new feature that makes the selection process even more effective. Products selected in this way can be directly simulated on circuits using the free online tool "Powere SIM," accelerating the development process.
Product identification and implementation have been simplified!
Author:
By: Steffen Hering, A&P Product Management,
Renesas Electronics Europe
