The MOSFET always rings twice – designing with synchronous converters


Acting alone may be a mark of individuality, but acting synchronously is a work of art. We see synchronicity in action all around us, in art, in nature and sports. We see this synchronous action, for instance, in ballroom dancing. Two dancers have to synchronize their moves carefully; if they don’t, their performance will fail. We watch with abated breadth how two trapeze artists synchronize their movements. The slightest mismatch of timing could result in disastrous results. Synchronicity is hard, but it is rewarding.

The two integrated MOSFETs in the sixth generation SIMPLE SWITCHER® devices always turn on twice with each switching cycle. The two MOSFETs, which are electronic switches, turn on and off in a very carefully designed, orchestrated move in synchronized action. This aspect of synchronous turn on and off is important and merits its own product category, synchronous DC-to-DC switch-mode power converters. Designing synchronous converters with two MOSFET switches integrated on the monolithic silicon is a challenge. The two MOSFET’s have to turn on and off, taking the responsibility of supplying the current to the output through the inductor. Each MOSFET needs to be in synch with the other so that they do not accidentally turn on at the same time, which could be disastrous and lead to burning the chip. The MOSFETs need to have a small time gap where they are both off, which is called dead time. This dead time needs to be of just the right duration - if it is too short, both MOSFETs risk turning on at the same time; if it is too long, it would have a negative effect on overall efficiency. This is a tight dance that the two MOSFET’s have to do—they need to act in unison and synchronize their actions. This delivers the best possible performance to the design.

Try out the new synchronous converters in your next design.  For a 60V input, you can use the LM46000, LM46001 or LM46002, for 0.5A, 2A or 3A loads respectively. For a lower 36V input, you can use the LM43600, LM43601, LM43602 or LM43603 for 0.5A, 1A, 2A or 3A loads. Check out a blog by my colleague Adam Castaldo for more information.

The new SIMPLE SWITCHER converters are integrated into our WEBENCH® Power Designer tools to make designing with them even simpler.  The tool not only creates the design for you, but also creates the full PCB layout that can be downloaded into your preferred CAD tool to get your product to market very fast. Watch a video by my colleague Kevin Ip where he shows how to use the new PCB Export feature in WEBENCH.

Try out the new SIMPLE SWITCHER converters using the WEBENCH tools and PCB Export in your next synchronous design. I’d love to hear how they work for you - please post a comment below.