PCIM Europe 2013, 14 – 16 May 2013, Nuremberg A new high voltage half bridge driver IC concept for consumer electronics and home appliances Wolfgang Frank*, Viktor. Boguszewicz, Rolf. Buckhorst, *Infineon Technologies AG, Am Campeon 1-12, 85579 Neubiberg, Germany, [email protected] Abstract Consumer electronic applications, computing and home appliances strive continuously for higher efficiency of applications and smaller form factors. A new family of half bridge gate drive IC is described, which supports this. Additionally, an integrated bootstrap function is presented for the first time in the market for driver IC with more than 2A output current. The high voltage gate drive IC family contains two current classes with output currents of 0.5A and 2.3A. This paper will point out the operation range and properties of the bootstrap function in terms of dependency on temperature and IC supply. 1. Introduction Only a few half bridge driver IC ([1], [2]) offer so far integrated bootstrap function for the high side supply. The reasons are a rather high voltage drop at low duty cycles and the additional high power dissipation in the IC at high switching frequencies. These devices are therefore limited to applications, such as consumer drives. These kind of driver IC are covering the market of 600 V blocking voltage, which is the low power drives market. Other half bridge driver IC, which do not have an integrated bootstrap diode, such as [3], [4] are covering the low end switch mode power supply (SMPS) applications. Since there is no bootstrap function integrated into the IC, these products have a slightly better temperature budget due to less power dissipation. However, the advantages of a powerful integrated bootstrap function are striking: simpler layout, less PCB space and better component placement in respect of distance to the gate terminal of the power transistor. This keeps also the EMI low and optimizes the switching performance, hence the switching losses. This paper proposes a new concept of a half bridge gate drive IC, which fully supports the design considerations of consumer electronic equipment and home appliance drive systems. The new half bridge driver IC is designed to support all mega trends in low power drives designs, such as ease of use, short bill of materials at simultaneously high number of features. 2. Technology Gate Source Poly-Si Drain Oxide Doping Doping-well LOCOS Doping-well Buried Oxide Silicon Substrate Fig. 1. Silicon-On-Insulator transistor ISBN 978-3-8007-3505-1 © VDE VERLAG GMBH · Berlin · Offenbach 1268 PCIM Europe 2013, 14 – 16 May 2013, Nuremberg The Thin-Film-SOI (Silicon-On-Insulator) technology is an advanced technique for MOS/CMOS fabrications. Based on conventional bulk process the SOI technology uses an insulator called buried oxide underneath the active device layer, as shown in Fig. 1. The lateral insulation of elements inside the silicon film is achieved by a simple local oxidation (LOCOS) process. In this way all active device regions are fully insulated from each other. Thus, there is no need for CMOS-wells for preventing the “latch-up” effect. Additionally the leakage current and junction capacitances are reduced significantly. The small size of PN-junctions inside the thin silicon film leads also to higher switching speed. Table 1:GGDevices and characteristics of the thin-film-SOI process Element CMOS analogue transistors CMOS digital transistors SOI-PIN-diode Z-diodes Resistors Capacitor HV bootstrap SOI-diode High-voltage SOI-transistor Characteristics 30 V / 12 V / 5 V 5V 30 V 5.2 V 18.5 Ω/square – 7.5 kΩ /square 0.84 fF/μm² 600 V, -50 V 600 V (N-Channel) Different devices inside the individual silicon regions can be implemented as shown in Table 1. The presented technology contains 600 V devices like level-shift transistor and highvoltage bootstrap diode, which are also realized in the thin silicon film. The 600V voltage ability is achieved by special junction termination structures, which allow monolithic realization of circuits like half or full bridge drivers for 600V applications. 3. Device family The proposed new concept covers the full range of peak output currents from 0.5 A to 2.3 A. The 0.5 A category is available in SO8 package and SO14 package, while the 2.3 A category in only available in SO14. All products in SO8 package concentrate on providing a floating high side section with a limited functional set and feature set. A suitable part for SMPS is the 2EDL05I06BF, which does not have a dead time and interlock function, so that both the high side output and the low side output can be activated simultaneously. Table 2: Individual function set realized in new concept part number Ipk Asym. BS UVLO for EN /FLT UVLO diode 9 Yes IGBT 9 Yes IGBT 9 Yes IGBT Yes MOSFET 9 9 9 Yes IGBT 9 Yes MOSFET 9 PGND OCP DT Pack. 9 DSO8 9 DSO14 DSO8 9 DSO8 9 9 9 DSO14 9 9 9 DSO14 A full set of protection functions and features, such as an enable function, a failure indication, separate return path for the gate current (power ground) incl. an overcurrent protection (OCP), is realised in the 2 parts with high output current of 2.3 A. Therefore, all applications with higher integration and safety requirements can be addressed. 2EDL05I06PF 2EDL05I06PJ 2EDL05I06BF 2EDL05N06PF 2EDL23I06PJ 2EDL23N06PJ 0.5 A 0.5 A 0.5 A 0.5 A 2.3 A 2.3 A ISBN 978-3-8007-3505-1 © VDE VERLAG GMBH · Berlin · Offenbach 1269 PCIM Europe 2013, 14 – 16 May 2013, Nuremberg 4. Bootstrap diode There are several components in the market, which provide a bootstrap function ([1], [2]). So far, this is only realized by integrated high voltage MOSFET structures according to the left part in 0. The MOSFET structures are turned on and off in phase with the LS transistor. This is a crucial point, because the driver IC is neither aware of the delay times of the power transistors nor of the power factor of the motor. Thus, the control of the bootstrap FET must consider this by additional bootstrap delays. These delays reduce the available time for bootstrapping, so that the bootstrap voltage is further reduced. VBus vTBS VDD TBS VB HO CVDD VDD Driver IC CBS T2 DBS VB HO D1 LO GND VDD RLim vBS T1 VS VBus vDBS CVDD VDD 2EDLfamily vCE D2 CBS vBS T1 D1 VS T2 LO GND vCE D2 Fig. 2. Bootstrap circuit of a half bridge Another negative aspect of MOSFET used for bootstrapping is the temperature dependency of MOSFET over temperature. Usually, MOSFET double their RDS(on) – value when the junction temperature increases by 100 °C. This means, that the above mentioned situation gets worse even more. The higher RDS(on) causes also more power dissipation inside the driver IC as well and limits the thermal safe operation area in respect to switching frequency and gate charge. It can be seen in Fig. 3, that the bootstrap diode is superior to existing bootstrap functions as soon as the diode forward characteristic is above the MOSFET characteristic. This is the case for a forward current of approx. 5 mA – 10 mA under elevated temperature. Fig. 3. Bootstrap diode forward characteristic compared to MOSFET with Rds(on) = 100 : (black Tj = 25°C, dashed: Tj = 125°C) and Rds(on) = 200 : (orange, Tj = 25°C, dashed: Tj = 125°C) ISBN 978-3-8007-3505-1 © VDE VERLAG GMBH · Berlin · Offenbach 1270 PCIM Europe 2013, 14 – 16 May 2013, Nuremberg The effects of the output characteristics are visible in a diagram, which shows the nominal voltage reduction of the bootstrap capacitor voltage in respect to the supply voltage versus the duty cycle. As an example, a single half bridge configuration is used as a representative of a SMPS topology. A small duty cycle of the low side transistor or diode leads to an uncompleted recharging of the bootstrap capacitor CBS according to 0. As a consequence, the bootstrap voltage decreases until a new steady state operation is reached in respect to the supply voltage of the driver IC. Fig. 4 shows the diagram for operating conditions of switching frequency fp = 20 kHz and a bootstrap capacitor of CBS = 22 μF. 125°C 25°C Rbs = 30 : 125 : 200 : Rbs = 60 : 250 : 400 : Fig. 4. Calculation of steady state bootstrap capacitor voltage drop vs. duty cycle for a buck converter The left part in Fig. 4 shows the conditions at a junction temperature of Tj = 25°C and the right part shows the same parameter at Tj = 125°C. The proposed driver IC concept realizes a bootstrap resistance of RBS = 30 : at a junction temperature of Tj = 25°C, while other concepts have RBS = 125 :orRBS = 200 : It is assumed for reasons of simplicity, that also the bipolar drift region resistance of a pn-diode doubles its resistance every 100°C. Please note, that the size of the bootstrap capacitor is not influencing the diagrams of Fig. 4. It only influences the transition phase from one bias point to another. The influence of the low resistance of the new driver IC is significant. It is easy to see, that the new driver IC concept is much more stable against high junction temperatures. The usable duty cycle range can go down to 1% with the new driver concept, without coming into an undervoltage lockout area. Other driver IC cannot serve duty cycle ranges below 4% (Rbs = 125 :) or 7% (Rbs = 200:). It means, that many applications, which requires operating at low duty cycles cannot use these IC. This is the case e.g. for SMPS operating is hard switching under high load condition or drive systems, which operate with high torque at low speed in field oriented control. In these examples the control is either in steady state or quasi steady state operating in the critical duty cycle range. 5. Asymmetric undervoltage lockout The new driver IC come along with dedicated designs for operation with IGBT. Well known market relevant driver IC only support MOSFET transistors in respect with the undervoltage lockout (UVLO) function. Gate threshold voltage of MOSFET (approx. 3 V, [5]) compared with IGBT (approx. 4.6 V – 5 V, [6]) allows to operate MOSFET with much lower gate voltages. This is represented as well in the UVLO levels of driver IC. On the other hand, it is dangerous to operate IGBT with driver IC, which provide MOSFET UVLO levels, because the MOSFET UVLO levels are so low, that the IGBT partially or fully desaturates. This effect causes highly increased losses and temporary operation in this mode can cause severe ISBN 978-3-8007-3505-1 © VDE VERLAG GMBH · Berlin · Offenbach 1271 PCIM Europe 2013, 14 – 16 May 2013, Nuremberg damage at the IGBT. It is therefore essential to operate IGBT only with driver IC, which provide suitable UVLO levels for IGBT. An important aspect of the design of undervoltage lockout (UVLO) levels is the support of integrated bootstrap diodes. They have a relatively high forward voltage drop which contributes to the bootstrap voltage reduction compared to the supply voltage VDD of the IC according to Fig. 4. The static bootstrap voltage vBS is in total vBS VDD vDBS vCE (1) where vCE is the transistor voltage of the low side transistor in a half bridge configuration. Please note that this converts into the diode forward voltage, when operating the low side diode. It is easy to see, that the highside output HO generates a smaller voltage, because the voltage vBS at the IC terminals VB and VS is reduced by the values vDBS and vCE. However, it is favourable to activate the UVLO for the high side supply VBS at a similar point of time as the low side supply VDD in order to prevent a insufficient supply of the high side gate. Therefore the low side UVLO is activated at approx. 1V higher levels as the high side UVLO function. It also allows shifting the shut down levels VCCUV- of the low side towards a little higher values. This can be achieved by implementing an asymmetric UVLO by considering different threshold for high side and low side as shown in Table 3. Table 3: Asymmetric high side and low side UVLO levels Parameter VCCUV+ VBSUV+ VCCUV– VBSUV– Min. [V] 11.8 10.9 10.9 10 6. Other helpful features 6.1. UVLO filter Typ. [V] 12.5 11.6 11.6 10.7 No UVLO Max. [V] 13.2 12.4 12.4 11 UVLO triggered VUVLO– t < tFILVDD or t < tFILVBS vDD vBS t 7.5 V t < tFILVDD or t < tFILVBS t > tFILVDD or t > tFILVBS vHOx t Fig. 5. Calculation of steady state bootstrap capacitor voltage drop vs. duty cycle for a buck converter It is often very difficult for design engineers to realise a good trade-off with system boundaries, such as geometry and component placement in order to achieve the best performance. An important item is the placement of the blocking capacitors for the supply voltages VDD and VBS. The above mentioned restrictions lead often to some distance between the IC and ISBN 978-3-8007-3505-1 © VDE VERLAG GMBH · Berlin · Offenbach 1272 PCIM Europe 2013, 14 – 16 May 2013, Nuremberg the blocking capacitor. This can cause inductive voltage drops at the pin VDD or VB during the turn-on transient with the consequence of undesired UVLO events according to Fig. 5. Therefore, a filter is suppressing such short time voltage drops and makes the IC more robust against noise on the supply lines. This is shown as an example in the very left side of Fig. 5. The filter time is approximately 1.5 μs, which is enough to filter all regular transients in respect with switching transients. However, the IC will control an UVLO and therefore the turn-off of the correlated outputs, if the voltage drop is lower than 7.5 V, which is given in the middle of Fig. 5. The IC will also shut down its outputs, if the voltage drop is longer than the filter time. 6.2. Active shut down The active shut down function is activated as soon as the supply voltage either on VDD or VBS reaches 3 V – 4 V. Leakage currents which may flow via the gate-collector path can potentially turn-on the device. The proposed concept clamps any leakage current of IGBT gate or MOSFET gate to the supply pin. The sink transistor inside the driver IC is activated, when the supply voltage exceeds approx. 3 V. The sink transistor is operated in its linear region and will clamp the gate. Small leakage currents in the range of μA can be clamped very efficiently as shown in 0. As a consequence, gate-emitter resistors can be omitted. 1200 I_LO μA 1000 I_HO 800 600 ILO IHO 400 200 0 0 1 VHO, VLO 2 3 4 5 V 6 Fig. 6. Calculation of steady state bootstrap capacitor voltage drop vs. duty cycle for a buck converter 7. Conclusion A new driver IC concept for half bridge configurations is proposed in this paper for home appliances and consumer electronics. It is optimised for the two mostly used transistor technologies, IGBT and MOSFET. The integrated bootstrap diode has a very low ohmic series resistance and hence enables the widest operating range in respect with controlled duty cycles. The bootstrap diode dissipates only little power inside the IC. This makes this IC to a benchmark in the market. Further functions, such as the asymmetric undervoltage lockout or the active shut down support especially IGBT help to match restrictions in terms of component placement and performance. 8. [1] [2] [3] [4] [5] [6] Literature STMicro: L6384; datasheet, STMicro, Italy, 2000 International Rectifier: IRS2607DSPbF, datasheet, International Rectifier, USA, 2008 International Rectifier: IRS2308(S)PbF, datasheet, International Rectifier, USA, 2006 Fairchild Semiconductor: FAN7382, datasheet, Fairchild Semiconductor, USA, 2007 Infineon Technologies: IPP60R600C6, datasheet, Infineon Technologies, Germany, 2012 Infineon Technologies: IKD04N60RF, datasheet, Infineon Technologies, Germany, 2012 ISBN 978-3-8007-3505-1 © VDE VERLAG GMBH · Berlin · Offenbach 1273