New isolated DC/DC converter offers programmable outputs for SiC drive applications

Apr 5, 2024
A worker monitors a robotic arm welding metal components in an industrial setting
There’s no doubt that wide bandgap (WBG) technology is here to stay. Silicon carbide (SiC) and gallium nitride (GaN) transistors are rapidly becoming the preferred choice in a wide range of industrial, consumer, and other power applications.

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Since SiC and GaN aren’t mature technologies like silicon, standards are still changing as manufacturers improve performance with each successive generation. For example, first, second, and third generation SiC devices are available on the market from different manufacturers and each generation has a different voltage combination needed to turn the device on and off.

This presents a problem for both the gate drivers and for the isolated DC/DC converters used to supply power to the gate drivers. These DC/DC converters typically use an internal transformer to provide isolation. The transformer is designed with a fixed ratio to supply the bias voltage appropriate for the gate driver being used.

As a result, one DC/DC converter is needed to supply one SiC device with turn-on and turn-off voltages of +15V and -8V; a different converter is needed to supply another SiC device with voltages of +15V and -3V. If both combinations are available as standard products that isn’t a problem, but if a new DC/DC converter design is needed, the schedule may be impacted, and safety recertification may be required. The unit cost is also likely to increase due to lower production volumes.

R24C2T25 simplifies SiC selection and evaluation

RECOM’s R24C2T25 series with USPs listed
RECOM’s R24C2T25 2W isolated DC/DC converter simplifies the design of WBG gate drive bias supplies (Source: RECOM)
A new product from RECOM allows customers to evaluate and use multiple types of SiC power transistors without expensive and time-consuming design changes. The R24C2T25 isolated DC/DC converter offers asymmetric regulated outputs that suit IGBT, Si, SiC, and GaN cascode gate drives. The outputs are programmable using external resistor networks.

One output can be set between +2.5 and +22.5VDC and the other between -2.5 and -22.5VDC with an overall positive to negative voltage of 18 to 25VDC, for example +15/-3V, to drive SiC gates efficiently.

As well as letting customers choose between different SiC devices, programmability also gives customers additional flexibility during the development phase. For example, customers can vary the switching voltage for a selected SiC device and decide which voltage they want to switch at based on empirical testing. Voltages are maintained within +/-1.5%, preventing the risk of over-voltage and damage. Total power available is 2W up to 82°C ambient with 2.5W available to 75°C. Useful derated power is also available to the package maximum of 125°C.

Isolation of the R24C2T25 is 3kVAC/1min with an ultra-low coupling capacitance of 3.5pF and a common mode transient immunity of +/-150kV/µs. This makes the parts ideal for powering high-side gate drives with fast dV/dt and dI/dt power switch edge rates.

The R24C2T25 features soft start, input under-voltage and over-voltage lockout, thermal shutdown, and output over-power protection. Output over-voltage and under-voltage lockout are also provided to ensure power devices cannot be stressed by invalid gate voltages. A power-good signal is provided along with ON/OFF control to put the device into standby mode with less than 700µA current draw.

In addition to programmability, the R24C2T25 features another advance compared to its predecessors: the use of surface mount technology (SMT) in the form of a compact 7.5 x 12.83mm 36-pin SSO-package. A surface mount package is highly desired by designers because it offers numerous advantages versus equivalent through-hole devices:

  • Space efficiency: SMT DC/DC converters are typically smaller in size, allowing for a more compact design. This is crucial in applications where board space is limited, such as in portable devices or miniaturized electronics.
  • High power density: surface mount packages contribute to higher power density on the PCB, enabling the creation of more powerful converters within a given space.
  • Improved thermal performance: Direct contact with the PCB enhances thermal conductivity, leading to better heat dissipation.
  • Enhanced high-frequency performance: SMT technology reduces lead lengths and parasitic effects, contributing to improved high-frequency performance of the converter. This is beneficial for applications where fast switching speeds are required.
  • Automated assembly: surface mount technology supports automated assembly processes, making the production of DC/DC converters more efficient and cost-effective.
  • Lighter weight: SMT packages are generally lighter than through-hole counterparts, which is advantageous in applications where weight is a critical factor, such as in aerospace or automotive applications.
  • Reduced electromagnetic interference (EMI): SMT components, with their shorter leads and compact layout, can help minimize electromagnetic interference, improving the overall electromagnetic compatibility (EMC) of the system.
  • Cost-effective production: the automated assembly and smaller form factor contribute to cost-effective production, as it reduces manufacturing time and material costs.
  • Higher component density: SMT packages allow for higher component density on the PCB, enabling the integration of additional features or functions into the same space.

Conclusion

Providing precision gate drive voltages is vital, especially for the latest generation of SiC devices. The R24C2T25 isolated DC/DC converter’s programmable outputs allow customers evaluate different devices and set the optimum voltage levels for the best combination of system efficiency and safety. The surface mount package also provides a host of benefits, improving efficiency, enhancing EMI performance, and reducing the size of the design.
Applications
  Series
1 DC/DC, 2.5 W, Single/dual Output, SMD R24C2T25 Series
Focus
  • 2W isolated DC/DC converter
  • Programmable asymmetrical output voltages
  • Ideal for IGBT/Si/SiC/GaN gate drive bias voltages
  • High 3kVAC/1min isolation