Project Analog - April 2008 - (Page 9)

McP1401/02 MosfEt drivErs the frequency of operation yields a value for average current. Figure 2 illustrates a point that was discussed earlier. Namely, as bias voltage increases, the crossover constant increases and, consequently, the power dissipation in the driver (due to cross-conduction) increases. Therefore, a decrease in driver voltage will result in a decrease in driver power dissipation. One thing to make note of is that when using a dual driver, the crossover constant is usually shown for both portions of the driver operating. If only one portion of the driver is being used, or the two portions of the driver are operating at different frequencies, be sure to use only half the value for each portion of the driver. Using the information illustrated in Figure 2 as an example, we will assume it is for a single-output driver operating with a VDD of 12V, at a frequency of 250 kHz. Based on the graph, the crossover constant is found to be 5.2*10-9. EQuation 7 PS = CC x F x V PS = 5.2 x 10–9 x 250 x 103 x 12 PS = 15.6mW For this driver, operating at this voltage and frequency, the power dissipation is relatively insignificant. Typically, as the current drive capability of the MOSFET driver increases, the losses due to shoot-through current will also increase. These losses can be significant and need to be taken into account when selecting a package for the MOSFET driver. conclusion There are many parameters to consider when matching the appropriate MOSFET driver to the MOSFET in your application. As with any electrical device, no one device is appropriate for every application, which is why Microchip Technology offers a wide variety of MOSFET drivers in a variety of packages, current ratings, output drive polarities and input logic configurations to suit your design needs. Contents Viewpoint Calculating Power Dissipation Accelerating Amplifier Design Driving Power MOSFETs Analog news The MCP1401 and MCP1402 are high speed MOSFET drivers capable of providing 500 mA of peak current. The inverting or non-inverting single channel output is directly controlled from either TTL or CMOS (3V to 18V). These devices also feature low shootthrough current, matched rise/fall times and propagation delays which make them ideal for high switching frequency applications Applications: • Switch Mode Power Supplies • Pulse Transformer Drive • Line Drivers • Motor and Solenoid Drive • Microchip analog page MOSFET driver overview Sample center microchipDIRECT Reference designs/ app notes Technical training 9 · 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

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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