Industrial DC/DC converters require more functionality

March 15, 2016 // By Oliver Nachbaur
High efficiency with the FlipChip QFN of TPS62097
Oliver Nachbaur, Technical Business Development Manager for the Low Power DCDC group at Texas Instruments Deutschland GmbH, explains how modern packaging technology can help improve the performance of industrial DC/DC converters that require more functionality.

When using a step down DC/DC converter in industrial applications the ideal device can be used across several platforms and applications. This is especially true for a multipurpose 2 A buck converter, like the new TPS62097. There are a number of 2 A buck converters on the market, but the choice becomes very limited when the overall solution needs to be small. One of the main obstacles is the limited pin count with small packages facilitating all device features. This article will outline key application features making the TPS62097 ideal for use across several application platforms.  We will discuss package construction of the new HotRod (QFN), highlighting its advantages, as well as taking a look at general reflow soldering guidelines for this new package.   

HotRod (QFN, DFN) packages allow higher converter efficiency

QFN (Quad Flat No-lead) and DFN (Dual Flat No-lead) packages have been around for quite some time. The next evolution is the advanced construction of the HotRod QFN or HotRod DFN, which has better electrical characteristics achieving higher efficiency.

A DC/DC switching converter achieves higher efficiency when switching losses are minimized. Switching losses are minimized when rise and fall time of the switch is fast in relation to the switching period. This leads to a higher switching speed with higher switching frequencies of the converter. Today’s rise and fall times of switching DC/DC converter are in the lower nanosecond range. This requires low parasitic lead inductance of the package in order to minimize over and undershoots of the switch node. Switch node over and undershoot should not exceed the process voltage rating and should be kept low in order to minimize EMI (Electro Magnetic Interference). Figure 1 shows the traditional QFN/DFN package.   

Figure 1. QFN Package (Quad Flat No-lead)

The cross section of the QFN package in Figure 1 shows bond wires connecting the die to the leadframe and device pins. The bond wire inductance will always be present and sets a limit for the switching speed of the DC/DC converter. The HotRod (QFN) package in Figure 2 does not require bond wires thus minimizing parasitic inductance.

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