Project Analog - April 2008 - (Page 6)

McP14E3/4/5 MosfEt drivErs The MCP14E3, MCP14E4 and MCP14E5 drivers are capable of operating from a 4.5V to 18V single power supply and can easily charge and discharge 2200 pF gate capacitance in under 15 ns. They provide low impedance in both the on and off states to ensure the MOSFET’s intended state will not be affected, even by large transients. In addition, control of the driver outputs is allowed by the use of separate enable functions. Applications: • Switch Mode Power Supplies • Pulse Transformer Drive • Line Drivers • Motor and Solenoid Drive 2. Power dissipation due to quiescent current draw of the MOSFET driver. EQuation 2 PQ = (IQH x D + IQL x (I-D)) x VDD Where: IQH = Quiescent curent of the driver with the input in the high state D = Duty cycle of the switching waveform IQL = Quiescent current of the driver with the input in the low side 3. Power dissipation due to cross-conduction (shootthrough) current in the MOSFET driver. EQuation 3 Contents Viewpoint Calculating Power Dissipation Accelerating Amplifier Design Driving Power MOSFETs Analog news There are three elements of power dissipation in a MOSFET driver: 1. Power dissipation due to the charging and discharging of the gate capacitance of the MOSFET. EQuation 1 PC = CG Where: CG = VDD = F = 6 · prOjECT ANAlOg · Apr 08 PS = CC x F x VDD Where: CC = Crossover constant (A*sec) As deduced from the equations, only one of the three elements of power dissipation is due to the charging and discharging of the MOSFET gate capacitance. This portion of the power dissipation is typically the highest, especially at lower switching frequencies. In order to calculate a value for Equation 1, the gate capacitance of the MOSFET is required. The gate capacitance of a MOSFET is comprised of two capacitances: the gate-to-source capacitance and the Microchip analog page MOSFET driver overview Sample center microchipDIRECT Reference designs/ app notes Technical training x VDD2 x F MOSFET Gate Capacitance Supply Voltage of MOSFET Driver (V) Switching Frequency http://www.microchip.com 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

Table of Contents Feed for the Digital Edition of Project Analog - April 2008

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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