Half-bridge PowerBlock achieves 2% efficiency boost due to packaging

The major application for low-voltage, high-current, high-frequency switching is in half-bridge switching configurations for synchronous buck converters, so it makes sense to optimize a package for just that application.Enter TI’s NexFET-based CSD86350Q5D Power Block, a synchronous MOSFET half-bridge with two percent better efficiency than competitive power MOSFET devices in half the area. The device, which consists of two asymmetric NexFET power MOSFETs, owes its efficiency to an advanced packaging technology that  targets low voltage synchronous buck half bridge applications.What about those competitive devices? Are they weak straw men chosen by TI to make the new part look good? No, TI makes the comparison to its own discrete version of NexFETs, an indication of the importance of packaging in the next generation of power management devices.Jeff Sherman, power stage marketing engineer for TI, says “We chose discrete NexFET devices with very similar Rds(on). The silicon isn’t identical [to the discrete versions] because there are some improvements inside the silicon within the PowerBlock, but most of the improvements seen in [PowerBlock performance] comes from the improved switching characteristics due to the reduced inductance between devices.”Rather than laying out the two FETs side-by-side, the two FETs are vertically mounted on top of each other., which makes for a shorter connection between the two, resulting in lower parasitic, a major cause of switching devices. But in addition to the shorter path, the vertical mounting allows the use of copper clips, resulting in the  lower inductance than do wire-bond leads, as Jeff refers to above. So, the Rds(on) is similar as is the parasitic capacitances, but the lower inductance results in the 2% increase in efficiency which translates to  20% less power loss. (f=500kHz, I = 25A.) The part is rated at 1.5 MHz.In addition, the exposed ground pad on the bottom of the package mounts directly on the pc board, for a simpler board layout.Jeff points out that multi-chip modules (MCMs) have been around for years in the power market, but they commanded premium pricing. “There isn’t a premium for this package. You’re getting better performance, smaller space, and it’s not going to cost you anything.”Instead of a second source, TI has two separate supply chains that can fab and assemble the device. Suggested resale pricing for the CSD86350Q5D is $1.75 in 1,000-unit quantities.