SNVA935A June 2020 – July 2021 LM60430 , LM60430-Q1 , LM60440 , LM60440-Q1
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Enhanced HotRod QFN is the latest advancement in semiconductor packaging which enables the industry's smallest 4-A, 36-V step-down converter. Figure 1-1 shows the semiconductor packaging technology evolution for high-power density step-down converters. The LM43603 was developed in a leaded HTSSOP package which uses a ground DAP for optimal thermal dissipation through the bottom side of the package. Second, the LMR23630 was released in a standard QFN package to eliminate the external leads while still having a thermal DAP. Consequently, the LMR23630 package size decreased by 73% compared to the previous generation converter. Third, the flip-chip on lead-frame (FCOL) technology has further improved the package-to-die ratio and removed package wirebonds connecting die to lead-frame to provide best-in-class noise performance. The Enhanced HotRod QFN package leverages the noise improvements of the FCOL package (Section 2) and the thermal advantages of the standard QFN package (Section 4). Figure 1-2 highlights the enhancements from FCOL and standard QFN packages to 'Enhanced' QFN. The latest TI part developed with Enhanced HotRod QFN package technology is the LM60440 device. It has a 4-A output current capability in an ultra-small 3-mm × 2mm package.
MOSFET technologies for wide input DC/DC converters enable the design of fast switching and high-efficiency power systems. Consequently, the latest DC/DC converters lead to fast switch voltage slew rates (dv/dt) and high-current slew rates (di/dt) which exacerbates the EMI emissions from a switch mode power supply and can cause problems to peripheral modules. For more details on the sources of EMI in DC/DC converters see the EMI Guide technical article series. EMI filters are inevitably part of a power electronic system, but since filtering adds unwanted size and cost, it is incumbent on the designer to look for all possible avenues including package technology for EMI noise reduction and mitigation. Regulatory compliance to electromagnetic compatibility (EMC) standards—for example, CISPR 32 for multimedia equipment and CISPR 25 for automotive applications is vitally important, as the efforts required to achieve compliance affect both product development costs and time to market. CISPR-25 is one of the most stringent emission standards for vehicles and devices targeting radio disturbance characteristics. The limits and methods of measurements are intended to protect onboard receivers from disturbances produced by components, such as a switching regulator in a power-supply design. For a deeper understanding of CISPR and other emission standards, see An overview of conducted EMI specifications for power supplies and An overview of radiated EMI specifications for power supplies white papers.
Low-EMI switching regulators utilize package technology, optimized pin-outs, and layout guidelines to minimize conducted and radiated noise from DC/DC converters which can enhances power system's performance to meet stringent EMI standards. TI's latest converter, LM60440, leverages the latest Enhanced HotRod QFN technology, and the pinout and package of the LM60440 regulator have been diligently optimized to minimize the parasitic inductance of switching loops to achieve the best-in-class low-noise performance.
As discussed in Section 1, the Enhanced HotRod QFN package has evolved from the standard QFN package and the FCOL package. Before delving into the latest package technology, it is important to understand the merits of the construction of each of its parent packages.
A standard QFN package has wire-bonds connecting the silicon to the lead frame (Figure 2-1). These wire-bonds can have inductance in order of 2 nH, and during a switching event, its commutating current can be in the order of 2 A/ns which can result in voltage overshoot up to 4–5 V on switch-node. Furthermore, device package wire bonds contribute significantly to the parasitic inductance of the power loop where fast switching (current and voltage) edges—and possible leading-edge ringing related to body diode reverse recovery and MOSFET COSS charging—is rich in harmonic content. The corresponding switch node ringing poses a severe threat of H-field and E-field coupling and consequently increases conducted and radiated emissions (Figure 2-2).
The LMR33630 utilized FCOL package technology, as shown in Figure 2-3, to eliminate the wire bonds by flipping the die on the lead frame to achieve the best possible EMI performance. The switch node waveform is shown in Figure 2-4 and the ringing has been eliminated. The trade-off of this technology is that the heat needs to dissipate through all the pins of the package. Due to the physical size limitation of each pin and absence of dedicated ground DAP for heat dissipation, the thermal performance of the FCOL package is limited compared to the standard QFN package. This observation is discussed in more detail in Section 4.
TI’s latest Enhanced HotRod QFN package offers next-generation technology to provide a low-EMI, high-power density solution in a standard QFN pinout for design familiarity and flexibility. The LM60440 and LM60440-Q1 devices are wide-VIN synchronous buck converters designed for low noise and EMI. The LM60440 device has an input voltage range of 3.8 V to 36 V capable of up to 4 A of load current. The LM60440 device has the same FCOL technology to eliminate the wire bond (expect same EMI performance), but utilizes a PowerPad (pin 13) consistent with a standard QFN package for better thermal relief and performance. In conclusion, Enhanced HotRod QFN package technology offers the best possible EMI performance and best possible thermal performance (as detailed in Section 4). In the following section, the Enhanced HotRod QFN Pin-Out (Figure 2-5) is examined in more detail.