Project Analog - April 2008 - (Page 21)

tc4426a/27a/28a MosfEt drivErs ensure that the power switch remains off unless it is safe to switch. Finally, the compound output stage provides both the high-current capability of bipolar transistors and the rail-to-rail voltage swing of MOSFETs. Typical waveforms of an IC driver are shown in Fig. 3, illustrating the high-current capability of a very small part, just 2 x 2 mm in this case. Thermally enhanced packages are often needed due to significant power dissipation in drivers, calculated simply as VDD times the total gate charge times the switching frequency. The cursors on these waveforms mark the drive current (green traces) at an output voltage of VDD/2, a more important rating than the peak drive current because a large portion of the switching time is spent in the Miller region, close to this voltage. A standard low-side driver has been used to illustrate the potential advantages of using any type of IC MOSFET driver in the design of switching power supplies. Contents fig 3 tyPical sourcing and sinking WavEforMs of a non-invErting ic drivEr With a coMPound outPut stagE. thE sharP sPikEs in thE outPut-voltagE WavEforMs arE Errors introducEd By thE tEst sEtuP. Viewpoint Calculating Power Dissipation Accelerating Amplifier Design Driving Power MOSFETs Analog news The TC4426A, TC4427A and TC4428A are 1.5A, dual high speed MOSFET drivers which can easily charge/discharge 1000 pF gate capacitances in under 30 ns. These devices provide low enough impedances in both the on and off states to ensure the MOSFET’s intended state will not be affected, even by large transients. Applications: • Switch Mode Power Supplies • Line Drivers • Pulse Transformer Drive While drivers may not make sense in the simplest, lowest-cost designs, their widespread use is proof that in many applications, they are a costeffective means of achieving higher efficiency, smaller size, higher reliability, and simpler design. Microchip analog page MOSFET driver overview Sample center microchipDIRECT Reference designs/ app notes Technical training • 21 · prOjECT ANAlOg · Apr 08 http://www.microchip.com http://www.microchip.com/analog http://www.microchip.com/analog http://www.microchip.com/mosfetdriver http://www.microchip.com/mosfetdriver http://sample.microchip.com/Default.aspx?testCookies=true http://www.microchipdirect.com/catalogselection.aspx?returnURL=default.aspx http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1423

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Project Analog - April 2008 Contents Viewpoint About Project Analog Sponsor Calculating Power Dissipation in a MOSFET Driver Accelerating Design of >50-W Class D Amplifiers Driving Power MOSFETs in Switch Mode Power Supplies Synergistic MOSFET Solutions Trends in MOSFET Gate Drivers Analog News—Analog news from multiple sources Enter to win an iPhone Contact Project Analog Sponsor Treelink Microchip Advanced Parts Selector (MAPS)

Project Analog - April 2008

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