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Posted on 02 July 2019

650V Super Junction Device with Rugged Body Diode

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Perfect for hard and soft switching applications

With the 650V CoolMOS™ CFD2 technology a benchmark is set for high voltage power MOSFETs with a high performance integrated body diode. The transistor combines a high blocking voltage of 650V with lowest Rdson and low capacitive losses together with an improved body diode ruggedness during reverse recovery especially for hard and soft switching applications. Together with the improved performance a specification of the max-value of the Qrr and trr in the datasheet will be introduced.

By M.-A. Kutschak and W. Jantscher, Infineon Technologies Austria AG, Siemensstraße 2, A-9500 Villach, Austria and D. Zipprick and A. Ludsteck-Pechloff, Infineon Technologies AG, Am Campeon 1-12, D-85579 Neubiberg, Germany

 

This article investigates the influence factors for improving the body diode ruggedness. The benefit of this Superjunction device family with fast body diode is especially shown for a HID half-bridge topology.

Introduction

With the increasing demand for higher power density, especially soft switching topologies like half-bridge (e.g. HID half-bridge or LLC) and full-bridge concepts (e.g. ZVS bridge) seem to be the ideal solution. These topologies reduce the switching losses and increase the reliability of the system due to less dynamic di/dt and dv/dt stress on the power device. Such high stresses occur predominantly in light-load operation [1]. It is already shown that Superjunction devices like the CoolMOS™ help to overcome this problem by inherent optimized charge carrier removal during reverse recovery and eliminating the problem of latch-up of the para-sitic npn-bipolar transistor [2]. A significant reduction of the reverse recovery charge can be achieved by an enhanced recombination rate of the injected carriers resulting in lower reverse recovery peak currents during turn-off and strongly reduced reverse recovery charge by almost a factor of 10. For optimized body diode (Figure1) performance in hard switching conditions, especially the shape of the resulting reverse recovery waveform and the design conditions of the printed circuit board are important [3-4]. The 650V CoolMOS™ CFD2 is designed in this manner with improved reverse recovery behavior together with increased safety margin in breakdown voltage.

Schematic cross section of the CoolMOS high voltage power MOSFET and its integral body diode

figure 1 caption

Reverse Recovery Behavior

The reverse recovery behavior of the new 650V CoolMOS™ CFD is shown in Figure 2. It appears that the new 650V CoolMOS™ CFD devices have a very low reverse recovery charge Qrr, reverse recovery time trr and maximum reverse recovery current Irrm when compared to the standard device.

Measured reverse recovery waveforms at di/dt=100A/ìs, 25°C, Vr=400V. The CFD device shows very low Qrr, trr and Irrm when compared to the standard device

At the same time, the waveforms of the new device still show a soft characteristic, in spite of the strongly reduced Qrr, trr and Irrm. This characteristic is highly desirable during hard com-mutation in order to avoid voltage overshoot and to ensure reliable device operation.

Commutation Ruggedness

The commutation ruggedness of the 650V CoolMOS™ CFD device is demonstrated in reverse recovery measurements in Fig. 3, where the devices were tested up to di/dt ≈ 2000A/μs.

Measured reverse recovery waveforms for the new 650V CoolMOS CFD2 de-vice

No device could be destroyed under these conditions and the waveforms show still a soft characteristic, compared to snappy waveforms for other superjunction devices. This is a clear advantage for the designer, once one can optimize its application for maximum performance without being concerned with device destruction during hard commutation of the body diode.

Dependence of Qrr and trr with temperature

Of utmost importance for the designer is the dependence of Qrr and trr on temperature. The Qrr and trr values tend to increase with temperature, due to increased carrier generation in the device. This dependence is shown in Figure 4 for the 310mΩ 650V CFD2 device. A linear in-crease of Qrr and trr with temperature is observed.

Dependence of Qrr and Trr with temperature for the 310mO 650V CFD device

Dependence of Qrr and Trr with Rdson

Another important aspect to be considered is the dependence of Qrr and trr on the device Rdson. This can be seen in Figure 5 and Figure 6, respectively, where the new 650V CFD2 device is compared with the former Infineon’s CoolMOS™ fast diode technology.

Dependence of Qrr on Rdson, measured at 25°C and for the 80, 310 and 660mÙ 650V CFD2 devices in comparison with the former 600V CFD technology

Dependence of trr on Rdson, measured at 25°C and for the 80, 310 and 660mÙ 650V CFD2 devices

The 650V CFD2 device clearly offers an even better trade-off then the former technology be-tween dynamical characteristics (Qrr, trr) and lowest Rdson.

Performance Evaluation in HID-Bridge

We have also compared the performance of the new devices with the commercial available SPD07N60C3 in a HID half-bridge application. Using the new CoolMOS™ CFD2 devices, the diodes D2, D3, D4 and D5 can be eliminated and allow reduced system costs (Figure 7).

Typical HID Half-Bridge circuit

For reference Figure 8 shows, the wave forms obtained by using the SPD07N60C3 device as transistors T2 and T3 and additionally the diodes D2, D3, D4 and D5. With this setup, we achieved an efficiency of 91,81%.

Circuit wave forms during the turn-off phase of transistor T3 with SPD07N60C3 as switch and the diodes D2 – D5 An efficiency of 91,81 percent is achieved.

By removing the diodes in series to the transistors, the additional voltage drop in forward op-eration is eliminated. This solution requires, however, an even superior performance of the internal body diode of the MOSFET once the switching losses increase due to the reverse recovery charge stored in the MOSFET. This situation is depicted in Figure 9.

Circuit wave forms during the turn-off phase of transistor T3 with SPD07N60C3 without the diodes D2–D5. An efficiency of 89,72% is achieved

In addition to increased switching losses, this setup also has the disadvantage that the MOSFET’s can eventually be destroyed due to the high reverse recovery current.

A superior solution is achieved by using the new IPD65R660CFD device. Due to the superior performance of the internal body diode of the MOSFET, it is possible to implement a solution without the diodes D2-D5 and obtain at the same time a considerably better efficiency. This is shown in Figure 10.

Circuit wave forms during the turn-off phase of transistor T3 with IPD65R660CFD without the diodes D2–D5. An efficiency of 92,81% is achieved

The optimized construction of the internal body diode of the new IPD65R660CFD device combined with a very low reverse recovery charge also enable reliable device operation.

Conclusion

Infineon’s CoolMOS™ CFD2 device, offers the lowest RDS(on) combined with a high blocking voltage of 650V. This new device features also a very low reverse recovery charge combined with a robust integral body diode. A specification of the max-values of the Qrr and trr will be available in the datasheet. We have also evaluated the performance of this new device in a typical HID Half-Bridge circuit, leaving out four diodes and getting superior efficiency. Due to the breakdown voltage of 650V and the robust construction of the integral body diode, this new device offers additional safety against destruction during hard commutation of the MOSFET.

 

References:

1) L. Saro, K. Dierberger and R.Redl, “Highvoltage MOSFET behavior in soft-switching converters: analysis and reliability improvements”, Proc. INTELEC 1998, pp. 30-40, San Francisco, Oct.1998.
2) W. Frank, F. Dahlquist. H. Kapels, M. Schmitt, G. Deboy, “Compensation MOSFETs with fast body diode – Benefits in Performance and Reliability in ZVS Applications“, Proceedings-CD of the International Power Electronics Component Systems Applications Conference (IPECSA), San Francisco, California, March 29 – April 1, 2019.
3) R. Ng, F.Udrea, K.Sheng, G.A.J.Amaratunga, “A Study of the CoolMOS Integral Diode: Analysis and Optimization”, The 24th International Semiconductor Conference; CAS 2001, October 2001, Sinaia, Romania.Grütz, A.: Jahrbuch Elektrotechnik '98. Berlin-Offenbach: VDE-Verlag, 1997.
4) R.K.Burra, K.Shenai, “CoolMOS Integral Diode: A Simple Analytical Reverse Recovery Model”, Power Electronics Specialist Conference, 2003. PESC '03. 2003 IEEE 34th Annual.

 

 

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