SiC Enables High Power Density in a Compact Package

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Apex Microtechnology has developed a family of devices with integrated silicon carbide (SiC) MOSFET technology, improving performance and power density.

Power applications are moving toward solutions featuring smaller footprint and higher efficiency. To increase the power density, which in turn allows the device to be housed in a smaller package, SiC is a good candidate for replacing silicon in power discretes and modules. Due to their superior properties, SiC MOSFETs are widely used in power applications in which high switching frequency, voltage, current, and efficiency are required.

Their ability to operate at junction temperatures higher than those withstood by silicon also allows SiC devices to achieve better thermal management, which is another advantage for shrinking the die size.

Silicon – based high – power discretes and modules normally require cooling solutions based on bulky heatsinks, which affect the size of the overall solution. On the other hand, SiC gives the opportunity to deliver unprecedented levels of power density in small – footprint packages without compromising thermal management.

Silicon Carbide

Compared with silicon, SiC offers several benefits, such as its lower on – resistance versus both temperature and current levels. A low RDS (on) results in a better current versus voltage performance and lower switching losses. Even though the cost of SiC is higher compared to silicon, its reduced thermal load, simpler cooling, and greater reliability compensate for this drawback.

Starting with these considerations, Apex – a provider of monolithic, hybrid, and open – frame analog power components for a wide range of industrial, test and measurement, medical, aerospace, semi-cap, and military applications – developed new products exploiting the properties of SiC. These products include the SA110, a half-bridge switching module with integrated gate driver, and the SA310, a three-phase power – switching module with integrated gate driver.

Proper design allows you to effectively highlight all the properties of SiC. In designing its high – power devices, Apex has carefully considered the effect of parasitics (which can exceed the on – resistance), trace inductance, and trace resistance. Figure 1 shows the block diagram of the Apex SA310KR, a SiC – based three-phase power module with integrated gate driver.

SiC
Figure 1: Block diagram of the SA310KR (Source: Apex Microtechnology (

One of the most demanding challenges faced by Apex during the design of the SiC – based power devices was the co – packaging of the MOSFET driver with MOSFET gate drivers. Due to the high switching frequency, which is one major capability offered by SiC, the current slew rate (di / dt) is very high. This requires a careful routing of traces on the PCB layout, avoiding the possible formation of noise or interference between adjacent traces (crosstalk).

Moreover, at higher switching frequencies, the skin effect is not negligible, as it can reduce the effective cross – sectional area of ​​the package’s input / output connections, increasing the electrical resistance. These potential issues have been solved by Apex by using an advanced thick – film technology on the substrate, double – printing the traces to thicken them and reduce their impedance.

A further advantage of Apex’s co – packaging solution is that the gate drivers are located very close to the SiC MOSFETs, thus reducing the effect of inductance in the gate, which becomes prominent at higher switching rates. By paying additional attention to thermal paths, packaging, and materials, the company has been able to achieve excellent thermal management, according to Apex. That allows, for instance, the SA110 to dissipate a power of 89 W, while operating in a temperature range from –40˚C to 125˚C.

The SA110, available in a small – footprint 12 – pin Power SIP (DP) package, features an integrated gate drive control, a very high (400 – kHz max) switching frequency, and 28 A of continuous output current in the A – grade variant. It is suitable for applications such as AC / DC and DC / DC converters, power factor correction (PFC), and motor drives.

The SA310, which comes in a 16 – pin Power DIP (KR) package, integrates three independent isolated half – bridges, which provide up to 80 A peak output current under direct microcontroller or DSC control. Built on a thermally conductive but electrically isolated substrate to provide the most versatility and ease in heatsinking, the SA310 addresses the requirements of applications such as motor control (BLDCs), variable – frequency drives, DC / AC converters, power inverters, test equipment, and MRI main coil supplies.

Both devices provide protection capabilities, such as undervoltage lockout function and active Miller clamping, to reduce switching noise and improve reliability.

Apex SA111

The Arizona – headquartered company has recently announced the SA111, a SiC – based high – power half – bridge module that delivers high levels of power density in a compact proprietary PQ package.

Available in an SMD package of just 20 × 20 mm, the SA111 (Figure 2) can provide continuous output currents of 32 A, manage supply voltages of up to 650 V, and achieve switching frequencies of up to 1 MHz (remaining in the safe operating area). The surface – mount package has a high thermal efficiency and top – side cooling. That allows the users to optimize the board layout, placing the heatsink directly on top of the device.

Figure 2: The new Apex SA111 (Source: Apex Microtechnology)

The SiC half – bridge power module is the ideal solution for applications such as MRI gradient coil drives, magnetic bearings, motor drives, test equipment, server fans, PFC, and AC / DC and DC / DC converters. SiC MOSFETs also enable the SA111 to withstand higher thermal stress, managing junction temperatures of up to 175˚C.

Featuring an integrated gate driver, undervoltage lockout, and active Miller clamping, the SA111 SiC power module is a fully integrated solution allowing for increased device control and protection. SiC greatly improves thermal management, as less heat is generated and there is thus less need for cooling of the module itself and the module can be smaller. Similarly, the power supply for the module can be smaller and dissipate less heat and likely be less expensive as well.

Thanks to its surface – mount package and exceptionally small footprint, the SA111 allows designers to maximize board real estate, allowing for the use of multiple devices in circuit designs with high power density requirements. Sample units of SA111PQ are currently available for qualified customer applications, with mass production volume ramp scheduled for summer 2022.

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