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Posted on 11 October 2019

IGBT Gate Driver Solutions for Low and Medium Power Applications

Gate drive and 500V 1A IGBT-FWD inverter in SOI-technology

 

Power electronics systems are commonly used in motor drive, power supply and power conversion applications. They cover a wide output power spectrum: from several hundred watts in small drives up to megawatts in wind power installations or large drive systems. Inside the system the gate driver circuit with its extensive control and monitoring functions forms the interface between the microcontroller and the power switches (IGBT). In this second part of the article fully integrated gate driver solutions for the low power range, their technologies, circuit aspects and specific designs are shown and discussed.

IGBT driver solutions for low and medium power applications (600V, 1200V, <50A) are aimed at high volume markets, where system costs and geometric size per function are the most relevant parameters. IC-based designs are thus replacing conventional hybrid IGBT drivers [4, 14, 15, 16]. For an asymmetric grounded DC link and low power applications, the microcontroller, the primary side, the emitter and secondary side gate driver of the low side switch (BOT) can be placed on the same ground potential. In this case a potential separation is only necessary for the secondary side of high side switch (TOP). System and high voltage IC design Figure 10 shows a typical block circuit diagram of a 3-phase power conversion system with an additional 7th channel at the low side to support power factor correction schemes or to be used as a brake chopper. The topological blocks to be integrated into a gate driver HVIC are marked (orange). Depending on the different applications only high side- [17], half-bridge [14] and six-pack driver ICs [4] are also possible, as well as the integration of additional blocks such as bootstrapdiodes or charge pumps for power supply and VCE detection diodes and circuits. The corresponding block diagram of a monolithic integrated 7-channel IGBT driver (Sevenpack) is given in Figure 11. Input interfaces (IIF) serve to process logic thresholds for direct connection to 5V or 3.3V microcontrollers. An interlock and dead time between TOP and BOT switch of a half-bridge is usually implemented in the external drive controller pattern but in many cases an additional hardware interlock and dead time is implemented in the gate driver as well as a short pulse suppression. Three 600V (or 1200V) level-shifters transfer the signals to the fully insulated high sides, where the differential transmission signals are filtered and reconstructed. The signals are driven at the chip output by a CMOS stage. The output currents (sink/source) vary from several hundred mA up to 4.5A [19]. The driver operates normally at 15V (Vop,max to 20V). The branch delay times of the six main channels TOP/BOT1-3 are delay-matched to ensure synchronized switching. Logic and error management generate the appropriate internal signals. These take into account not only under-voltage lockout (UVLO, primary and secondary side) as derived from a bandgapstabilized reference but also external analog sensor signals such as shunt current monitoring. Complete integration of an IGBT gate driver exit demands the following technological requirements:

• Insulation technology for the certain electrical separation of low- and high-side circuit blocks. Here PN-insulation [4, 14], dielectric insulation (SOI) [6] and mixed technologies of both [20] are used today.

• High-voltage devices of the 600V and 1200V class respectively, which can be used as level-shifter (no galvanic insulation). The lateral DMOS-transistor as classic RESURF (Figure 3) or as SOI-RESURF (Figure 5) device is the most common solution.

• Digital and analog circuits for operation voltages up to 20V for signal processing, control and driver functions on the low and particularly on the high side, where the ground potential is coupled on the emitter potential of the TOP switch and extreme voltage transients occur.

Power conversion system showing gate driver HVIC integration area

Figure 1. Power Conversion System showing Gate Driver HVIC Integration Area

Typical block diagram of a monolithic integrated IGBT driver for seven switches (seven pack driver)

Figure 2. Typical block Diagram of a monolithic Integrated IGBT driver for seven switches (sevenpack driver)

Gate driver in PN-insulation technology

The most important advantage of PNinsulation is that the device structures can be adjusted to the different voltage classes (600V, 1200V) by scaling of edge termination structure and doping concentration and depth of epitaxial layer, although of course the charges increase with the blocking voltage. This is shown in Figure 3 where the cross sections of the fundamental device structures are similar for the 600V and 1200V class, but the doping concentrations and distances are completely different. The full blocking voltage between high side and low side drops completely at the N- epitaxy / Psubstrate junction and its lateral edge termination structure. Because of the large depth of N- region a parasitic coupling of the buried PN-junction on the active circuits on the surface can be avoided, especially at floating high side (Figure 3 middle). This makes the realization of sensitive analog circuits on the TOP-secondary side possible.

Fundamental device structures of 600-1200V PN insulation technology

Figure 3. Fundamental device structures of 600-1200V PN insulation technology

Figure 4 shows chip photographs of different driver topologies, voltage and current classes of different manufactures. The insulated TOP secondary sides and their PN-edge termination structure around are clearly identifiable, as well as the driver output stages of every channel. In Figure 4 (left) and 4 (right) the differential level-shifters are embedded inside the termination structure while in Figure 4 (middle) the level-shifters are located separately. Though the market has shown
considerable interest in these compact and cheap high voltage driver ICs, the junction insulation has certain fundamental drawbacks. Negative transient voltages at the driver output can trigger internal parasitic thyristor structures, leading to
latch-up. The problem can be somewhat alleviated by minority carrier suppression structures [22, 23] but it cannot be resolved completely. Also, PN leakage currents which increase with a factor of 4 per 10K temperature rise increase the
losses and lead to an addition self-heating of the device which typically limits the operation temperature to 150°C.

Different ICs in PN-insulation technology

Figure 4. Different ICs in PN-insulation technology

Gate driver in SOI substrates

Appropriate high voltage silicon on insulator SOI-CMOS (600V) platform technology [24, 25] can provide complete latch-up immunity since all active devices are dielectrically insulated (see Figure 5). The regular CMOS circuits of the low side
and the high side are based on quasi-bulk transistors in fully isolated silicon islands. This enables the operational temperature range to be considerably extended up to 200°C [6]. The active silicon is thick enough to prevent punch-through of the back side space charge region to the top side devices. The keys to the high breakdown voltages are the thick buried oxide layer and the selective layer thinning in the drift region of the high voltage devices.

Schematic cross section of fundamental device structures of 600V SOI-CMOS technology

Figure 5. Schematic cross section of fundamental device structures of 600V SOI-CMOS technology

Advanced level shifter concept

Even in low current applications and, yet more, in medium and high current applications, where high currents or high di/dt are switched, positive and negative voltage peaks may occur on parasitic elements in the power plane. These voltage peaks might cause a strong voltage drop between the primary and the secondary side of the gate driver (offset voltage). A negative offset voltage in particular is critical for junction-isolated HVICs [18, 14], commonly allowing only a few volts (typically -5V) below ground potential to prevent latch up [4]. Therefore the design goal for medium power applications is a significant extension of the range of the operational voltage shift between the primary side (control logic) and the  secondary side (drivers). This requires an advanced level shifter concept for both the BOT and the TOP channel allowing “bipolar” operation. The circuit principle of the BOT channel level shifter is shown in Figure 6. It consists of two  independent transmission paths, an up-level shifter and a complementary down-level shifter. The configuration is that of a conventional static CMOS level shifter with additional diodes in each path. Both the up- and the downlevel shifters use two cross coupled parallel branches with the function of a latch. Hence there are no cross currents under static voltage conditions. Because of the full dielectric insulation of each device, the circuit itself is latch-up free. For this reason and also that of the weak back gate effect uplevel shifter (Voffset ≥ 0V) or the down-level shifter (Voffset ≤ 0V) transmits the applied  input signal from the primary to the secondary side. The inactive path is blocked by reverse-biased diodes. To reconstruct the signal on the secondary side, a simple logic disjunction can be  used. The circuit principle of the TOP channel level shifter is shown in Figure 7.

Circuit principle with up - down level shifter for the BOT channel

Figure 6. Circuit principle with up - down level shifter for the BOT channel

Circuit principle with up - down level shifter for the TOP channel

Figure 7. Circuit principle with up - down level shifter for the TOP channel

As in the case of the BOT channel, the level shifter consists of two complementary parts - the high voltage up-level shifter and the low voltage down-level shifter. Because there are no p-MOS devices available with a breakdown voltage extending to 600V, a pulsed signal transmission simply requiring  high-voltage n-DMOS transistors and high-voltage diodes, to block the high reverse voltage in the down-level shifter, is used.

600V/1.4A 7-channel gate driver IC in SOI-CMOS technology

Figure 8. 600V/1.4A 7-channel gate driver IC in SOI-CMOS technology

A pulsed transmission is applied to minimize the cross current and power consumption but requires more complex signal generation and reconstruction in comparison to the BOT channel. The differential transmission with two branches per level shifter, a robust signal processing and reconstruction on the secondary side provide maximum immunity  against parasitic coupling from the power plane.

Block diagram of a two-chip 1200V SOI half bridge gate driver

Figure 9. Block diagram of a two-chip 1200V SOI half bridge gate driver

Seven channel 600V gate driver design

Figure 8 shows the chip photograph of a 7-channel gate driver IC. It contains all the functionality needed for a 3-phase power system and a fourth independent BOT channel is implemented for PFC or brake chopper applications according to the power conversion system of Figure 10 and the block diagram of Figure 2. It is realized in a 600V CMOS-SOI technology [24] whose cross section is shown in Figure 14. The three insulated TOP secondary sides with their HV-DMOS- transistors and HV-diodes of up-/down- level shifter circuit (regarding Figure 7) are clearly to recognisable, as are the output stages of the 3 TOP and 4 BOT channels with 1.4A/1.4A (source/sink) peak current at reference voltages down to -45V (bottom channel) and -20V (top channel) respectively. The powerful output stages of every channel can drive the gates of 600V/50A IGBTs directly in  PM configurations [13].

Assembled two-chip 1200V SOI half bridge gate driver in a 1200V 50Asixpack IPM

Figure 10. Assembled two-chip 1200V SOI half bridge gate driver in a 1200V 50Asixpack IPM

Double pulse measurement

Figure 11. Double pulse measurement

Schematic cross section of fundamental device structures of 500V SOI-CMOS technology

Figure 12. Double pulse measurement

Each TOP channel has a separate bandgap reference and an UVLO circuit in order to monitor the high side operational voltage. This may be important if the TOP channels are powered by a bootstrap circuit. Advanced level shifter concept for 1200V CMOS-SOI gate drivers 600V gate drive ICs based on 600V SOI-CMOS can overcome most of the disadvantages of gate drive ICs which rely on conventional junction isolation. Nevertheless, SOI technologies for the 1200V class do not currently exist. For this reason a new concept for 1200V signal transmission and high side insulation has been developed and was implemented in the half-bridge gate driver IC here presented. The transmission of the control signals to the high side is based on a new 1200V level shifter topology with cascaded 600V transistors and without further signal processing on the originating intermediate potential. A balanced voltage division across the HV transistors during switching is achieved by a balanced capacitive divider. The  implemented active clamping circuitry prevents the exceeding of the maximum voltages. The limited breakdown voltage of the vertical dielectric insulation of the SOI substrate (BOX, Figure 5) requires the subdivision of the offset voltages on two physically separated dies and that, in turn, requires that all high side functions are integrated in a separate high-side IC. Figure 9 shows the block circuit diagram and Figure 19 the chip photography of a two-chip 1200V halfbridge gate driver. Exemplarily for the performance reached, Figure 11 shows a double pulse measurement of a 1200V/50A IGBT at 1200V DC link 15V supply voltage and room temperature. In comparison to the PNinsulation driver designs in Figure 13, the insulation distances between low side and high side are very small due to the dielectric insulation. The design is extremely compact and the fully dielectric insulation of each device leads to low leakage currents and high latchup ruggedness even at temperatures up to 200°C [6]. The capabilities of the level shifters are demonstrated experimentally in [13, 26]. The circuit remains operational for negative voltage and rated current (50A) with inductive load.

Gate drive and 500V 1A IGBT-FWD inverter in SOI-technology

Figure 13. Gate drive and 500V 1A IGBT-FWD inverter in SOI-technology

Driver and  inverter integration on a single chip

The fully dielectric insulation of every device in SOI-substrates enables also the integration of high-voltage bipolar devices like IGBTs and diodes together with driver and monitoring functions on the same chip. Figure 12 presents the cross section of the fundamental devices of this technology and Figure 13 the chip photograph of a 500V/1A inverter [27, 28 Mitsubishi]. For chip area and cooling reasons, such solutions are limited today on low power applications (several hundred watts).

References

[13] B. Vogler, M. Rossberg, R. Herzer, L. Reusser et al: 600V Converter/Inverter/Brake (CIB)-Module with integrated SOI Gate Driver IC for Medium Power Applications, Proc. CIPS 2008, pp. 261-266
[14] Data sheet, L 6384, ST Microelectronics, 2003
[15] Data sheet, SPM(tm) DIP-SPM, Fairchild Semiconductor, 2003
[16] Sung-il Yong, Bum-Seok Suh et al.: Power Systems Design Europe Issue September 2004, pp. 12-17
[17] Datasheet 600V,10A Super Mini DIP-IPM, Mitsubishi, 2006
[18] T. Takahashi: Power Conversion Processor(tm) Architecture and HVIC Technology for AC Motor Drive, Proc. CIPS 2000, pp. 73-81
[19] Data sheet, Half-Bridge Gate Drive IC FAN 7390M1, Fairchild Semiconductor, 2008
[20] R. Rudolf et al.:New Level-Shift-Transistors in 600V-Smart-Power ICs using Thin-Film SOI-Technology, Proc. CIPS 2002, pp. 89-94
[21] D. Tam: New 1200V Integrated Circuit Changes The Way 3-Phase Motor Drive Inverters Are Designed, IR Technical Paper, July 2008
[22] S. Gupta, J.C. Beckman, S.L. Kosier: Improved Latch Up Immunity in Junction-Isolated Smart Power ICs with Unbiased Guard Ring, IEEE Electron Device Letters, Vol. 22, No. 12, 2001
[23] J.P. Laine, O. Gonnard, G. Chariat, L. Bertolini et al. : Active Pull- Down Protection for full substrate current isolation in Smart Power ICs, Proceedings ISPSD 2002, pp. 273-276
[24] T. Letavic, E. Arnold, M. Simpson, R. Aquino et al.: High Performance 600V Smart Power Technology Based on Thin Layer Silicon-on-Insulator, Proceedings ISPSD 1997, pp. 49-52
[25] T. Letavic, M. Simpson, E. Arnold, E. Peters et al.: 600V Power Conversion System-on-a-Chip Based on Thin Layer Silicon-on-Insulator, Proceedings ISPSD 1999, pp. 325-328
[26] B. Vogler, M. Rossberg, R. Herzer: 600V SOI Gate Driver IC with advanced Level Shifter Concept for Medium and High Power Applications, Proceedings EPE 2007, Aalborg, Denmark
[27] T. Yamane, S. Ikeda, A. Nakagawa: Three-Phase Sinusoidal Current PWM Brushless Motor Driver ICs, Proc. ISPSD 2004, pp.147-150
[28] E. Motto, J. Dunlon, K.Watabe, H.Kazunari, T.Araki: A monolithic 500V, 1A Three Phase Motor Driver with Small Outline Surface Mount Package, Proc. of 42. IEEE Industry Applic. Conf. 2007, pp. 1047-1051
[29] M. Münzer, W. Ademmer, B. Strzalkowski: Coreless Transformer, a New Technology for Half Bridge Driver ICs, Proc. PCIM 2003
[30] R. Herzer, J. Lehmann, M. Rossberg, B. Vogler: Integrated Gate Driver Circuit Solutions, Power Electronics Europe July/August 2010, pp. 26-31

 

For more information, please read:

Connection of Gate Drivers to IGBT and Controller

IGBT Driver Calculation

Driver Units for Thyristors

 

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