Integrated multi-half-bridge drivers are becoming more popular as designers push the envelope on what’s possible within their ever-shrinking printed circuit board (PCB) designs. PCBs are getting smaller while power levels and feature requirements are growing. This leaves some engineers wondering whether it’s better to stick with their traditional discrete half-bridge design or move to a more integrated three-phase design such as the DRV8320. In this article, I’ll take a quick look at the pros and cons of this decision by looking at data that may help influence the selection of the right integrated circuit (IC) for brushless-DC motor drives.
Let’s start with a list of the differences between the integrated and discrete approaches. The designs that I’m comparing are the same ones used in Part 1 and Part 2 of this technical article series.
Discrete half-bridge gate-driver design
Integrated gate-driver design
Often, the PCB layout parasitic differences are the major design distinction between using integrated and discrete gate drivers. Conventional wisdom states that integrated layouts need longer gate and source traces, which causes the parasitic effects to be worse than a discrete approach.
Using modeling and simulation software, I analyzed the layouts compared in Part 2 of this series for parasitic inductance and resistance in order to get a true look at the differences between the designs. Figure 1 summarizes my findings.
Figure 1: Integrated vs. discrete gate-driver comparison (Note: The integrated approach has one closer half bridge [phase B] and two farther ones [phases A and C], while the discrete approach has the same layout copied three times. That is why the integrated design lists a minimum and maximum, while the discrete design lists only one value for each parameter.)
To my surprise, the parasitic inductance and impedance for integrated and discrete half-bridge gate drivers show very little difference. The integrated gate driver does not increase parasitic element values significantly. The benefits of essential protection, reduced BOM and reduced solution size still apply.
In summary, integrated gate drivers such as the DRV8320 are great candidates for reducing the size of discrete designs and are sure to put an elegant “spin” on your brushless-DC product.
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