| Specifications | Anatomy of Gate Charge Ralph C. McArthur |
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| Specifications | Anatomy of Gate Charge Ralph C. McArthur |
| Business section |
| Specifications | Anatomy of Gate Charge Ralph C. McArthur |
| Outline | Implications |
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| Content | APT0103 Rev - © 2001 Advanced Power Technology 1 Making Use of Gate Charge Information in MOSFET and IGBT Data Sheets Ralph McArthur Senior Applications Engineer Advanced Power Technology 405 S.W. Columbia Street Bend, Oregon 97702 Power MOSFETs and IGBTs have established themselves as premier power semiconductors in a wide range of applications involving switching or amplification. In order to use these devices effectively it is necessary to understand and make use of the gate charge information on the data sheet. This information appears in two lo- cations: in the “Dynamic Characteristics” sec- tion of listed parameters and in the figure show- ing gate-source voltage versus total gate charge. Hereafter the figure showing gate-source volt- age versus total gate charge will be referred to simply as “the gate charge curve.” This applica- tion note is written with MOSFETs in view, but everything said here applies to IGBTs as well. Just exchange “collector” for “drain” and “emit- ter” for “source.” The discussion is based on a common MOSFET model, shown in Figure 1. The figure shows the MOSFET model, the total gate resistance, and block elements for the load impedance and the gate drive circuit. Figure 2 shows a gate charge curve taken from a data sheet. It displays the gate-source voltage as a function of charge injected into the gate. Charge is built up in the gate as long as gate drive current flows into the gate. Note that the main power supply, VDD in the gate charge measurement, serves as a parameter in the fig- ure. Figure 1 shows where VDD is applied. The charge required to reach a certain gate voltage is different for different values of VDD. For a given VDD, if a certain number of nanocoulombs are in- jected into the gate, the voltage will rise to a certain level. Use of Figure 2 in gate drive design has al- ready been described.1 G D S Gate Drive Circuit DDV ZL RG CGD CGS CDS Figure 1. Lumped element model for a power MOSFET The gate charge parameters called out in the “Dy- namic Characteristics” section of the data sheet are as follows: Qg, the total gate charge, Qgs, the gate- source charge, and Qgd, the gate-drain (“Miller”) charge. Figure 3 shows the parts of the gate charge curve from which these charge values are taken. |
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| Following Datasheets | APT0201 (15 pages) APT0301 (15 pages) APT0302 (6 pages) APT0401 (3 pages) APT0402 (6 pages) APT0403 (12 pages) APT0405 (8 pages) APT0407 (5 pages) APT0408 (16 pages) APT0501 (5 pages) |
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