A good method is to dedicate one copper plane in a

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Unformatted text preview: turning ground current from the load to affect the logic line driving the driver IC. A good method is to dedicate one copper plane in a multilayered PCB to provide a ground surface. All ground points in the circuit should return to the same physical point to avoid generating differential ground potentials. With desired rise and fall times in the range of 25 to 50 ns, extreme care is required to keep lengths of current carrying conductors to the bare minimum. Since every inch of length adds approximately 20 nH of inductance, a di/dt of 240 Amps/microsecond (used in the example calculation for Eq. 5.1) generates a transient LdI/dt voltage of 4.8 volts per inch of wire length, which subtracts from the driver’s output. The real effect will be a significant increase in rise time for every tiny increase in conductor length from output pin of driver to the Gate lead of MOSFET/IGBT. For example, one extra inch of conductor length could increase rise time from 20 ns to 70 ns, in an ultra h igh-speed gate drive circuit. Another detrimental effect of longer conductor length is transmission line effect and resultant RFI/EMI. This inductance could also resonate with parasitic capacitances of MOSFET/IGBT, making it difficult to obtain clean current waveforms at rise and fall. It is important to also keep in mind the fact that every MOSFET/IGBT has some inductance depending on the package style and design. The lower this value, the better is the switching performance, as this inductance is, in effect, in series with the source/emitter and the resulting negative feedback increases switching times. While applying driver IC for any application, it is also necessary to compute power dissipated in the driver for a worst-case scenario. The total power dissipated in the driver IC is a sum of the following: 1. Capacitive load power dissipation; 2. Transition power dissipation; IXAN0009 3. Quiescent power dissipation. For all IXD_series of drivers, transition power dissipation is absent due to a unique method (Patent pending) to drive t...
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