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Use of lower MOSFET conduction and switching losses

In Electronic Infomation Category: U | on April 13,2011

Metal - oxide - semiconductor - field-effect transistors, referred to as the MOS transistor (Metal-Oxide-Semiconductor Field-Effect Transistor, MOSFET) is a widely used in analog circuits and IPS512G datasheet and digital circuits, field effect transistors (field-effect transistor).

Regulators and IPS512G price and end customers on the DC / DC power efficiency have become increasingly demanding, they require a lower on-resistance, and IPS512G suppliers and can not affect the unclamped inductive switching (UIS) capability or no increase in switching losses. Shielded gate MOSFET can range 30 ~ 200V DC / DC power supply designers to provide solutions. Now, by improving the switching performance, on-resistance Rds (on) has been able to reduce 50% or more, thereby enhancing efficiency and creating conditions for higher frequencies. This article discusses the medium-voltage shielded gate MOSFET MOSFET (40 ~ 300V) applications advantage.

Power design challenge

DC / DC designers have been faced with greater efficiency and power density of the challenge. The power MOSFET technology advances to help them to achieve this goal. On-resistance Rds (on) and gate charge Qg, in general, while another increase is always a decrease, so the power MOSFET design must take into account the trade-off between the two. A new process can be reduced trench MOSFET Rds (on), did not affect Qg. This technology is shielded gate technology. It can reduce the pressure in the on-resistance MOSFET key component - with the drain-source breakdown voltage (BVdss) the extension of resistance (epi resistance). Shown in Figure 1, this technology is particularly applicable to more than 100V applications.


Figure 1, the traditional trench technology Rds (on) in each component

Figure 1 shows the 30V and 100V rated the traditional trench MOSFETs Rds (on) component of the comparison. For the 100V device, Rds (on) the percentage is much greater in the extension component. The use of such a charge balance shielded gate technology, more than half of the extension resistance can be reduced, without increasing the total Qg or Qgd components.

Charge balance technology

Figure 2 on the traditional trench gate device with the shield cross section of the device were compared. A shield electrode through the integration of the latter to achieve charge balance, to support the voltage of the impedance and length of the region have been reduced, thereby significantly reducing Rds (on).


Figure 2 (a) the traditional devices (b) shielded trench gate charge balance structure

In addition, the shield electrode in the gate electrode, the latter to the bottom of most of the traditional trench MOSFET gate-drain capacitance (Cgd or Crss) are converted to gate-source capacitance (Cgs). So, put the shield gate electrode and drain electrode potential to isolate.

Figure 3 compares with the equivalent Rds (on) MOSFET and shielded the traditional trench MOSFET gate capacitance components. As Crss reduced switching from off to on state, or from the on-off switch to reduce the time required for the state, switching losses are therefore minimized. In particular, as shown in Figure 4, reducing the Qgd, the device can be both high pressure and high current loading time reduced to a minimum, thereby reducing the switching energy.


Figure 3 20A Rds (on) 5.7m the same conditions, the traditional devices and shielded gate trench capacitor component of the device compare


Figure 4 20A Rds (on) 5.7m the same conditions, the traditional trench devices and shielded gate trench device 20A/50V Qg curve when compared

In addition, the shielding layer and the impedance of the equivalent of a built-in buffer resistor (snubbing resistance, (Rshield)) - Capacitance (Cdshield) network, as shown in Figure 3, components are described in Coss. The buffer network can slow down the switch from low to high conversion speed. This feature helps to shield the gate during the switching converter to reduce EMI, dv / dt and avalanche caused by misleading pass effect.

DC / DC 1 / 16 brick module, performance improvement

The input voltage 48V, output 3.3V, operating frequency of 400kHz, the current range of 10 ~ 20A of the isolated DC / DC converter primary side, the shielding of the Fairchild FDMS86252 150V MOSFET gate compared with similar products. The results shown in Figure 5. Can be seen from the figure, the use of shielded gate technology, FDMS86252 can improve the efficiency of at least 0.4%, which means savings of at least 0.32W of power, seems insignificant, but the DC / DC design is crucial for important because to meet the relevant specifications, each percentage point of efficiency is very precious.


Figure 5 in a 48VVIN, 3.3VVOUT, 400kHz operating frequency of the isolated DC / DC converters, Fairchild FDMS86252 150V shielded gate MOSFET with similar products, compared

Summary

Compared to previous generations of technology, Fairchilds PowerTrench MOSFET technology new better Rds (on) and Qg. This technology enables power supply designers to improve the efficiency and power density to a new level.

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