AN2359 265VAC 88VAC 300VDC 120VDC 320VDC 374VDC -12V/-5V SRW0913 1N4007 BA157 - Datasheet Archive

 

Application note Double output Buck-Boost converter with VIPerX2A Introduction This paper introduces two off-line non-insulated

 

AN2359 AN2359 Application note Double output Buck-Boost converter with VIPerX2A Introduction This paper introduces two off-line non-insulated SMPS double outputs in Buck­Boost configuration based on VIPerX2A family The power supplies are operated in wide input voltage range, i.e. 88 to 265VAC 265VAC. They can supply small loads, such as a microcontroller, triacs, display and peripherals in the industrial segment and home appliance. In the applications where a double output is required, two different solutions can be used. The first one regards an insulated converter topology, with second output generated by means of one winding on the magnetic core of the inductor with a proper turns ratio. Nevertheless, this solution is expensive in terms of transformer and can be used for medium and high current or insulated applications. For low power and low cost applications, a non-insulated converter topology can be used. The proposed topology, based on Buck-Boost converter, is used to supply negative output voltage referred to neutral in all those applications where the galvanic insulation is not required. The principle schematic is shown in figure below. Proposed double output Buck-Boost topology VOUT1 is provided using the classic Buck-Boost configurations, while VOUT2 is obtained thanks to an intermediate tap on the inductor. Compared to other already proposed solutions, the second output is obtained thanks to an intermediate tap on a low cost inductor. This configuration limits the parasitic capacitive effect between the two winding and improves the regulation at open load. Further advantage is related to the regulation feedback connected on VOUT2. Thanks to this regulation, it is possible to cover those applications where a low tolerance and low voltage is required (i.e. a microcontroller) and a high tolerance and high voltage is required for the auxiliary circuit (drivers, relays.). December 2006 Rev 1 1/18 www.st.com Contents AN2359 AN2359 Contents 1 VIPerX2 description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 Output voltage selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 Application example nº 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1 3.2 4 Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Application example nº 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1 Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2/18 AN2359 AN2359 List of figures List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Converter schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Typical waveforms at 88VAC 88VAC: open load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Typical waveforms at 88VAC 88VAC: full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Typical waveforms at 265VAC 265VAC: open load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Typical waveforms at 265VAC 265VAC: full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Commutation at full load: 88VAC 88VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Commutation at full load: 265VAC 265VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Output ripple voltage at full load: 88VAC 88VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Output ripple voltage at full load: 265VAC 265VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Turn on losses measurement at full load: 88VAC 88VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Turn on losses measurement at full load: 265VAC 265VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 VIPer22A Thermal profile: at VIN= 88VAC 88VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 VIPer22A Thermal profile: at VIN= 265VAC 265VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 VIPer22A temperature at maximum load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Converter schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Typical waveforms at 300VDC 300VDC and full load: commutation . . . . . . . . . . . . . . . . . . . . . . . . . 15 Typical waveforms at 300VDC 300VDC and full load: detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 PCB Layout (not in scale). Option nº 1: -12V output voltage . . . . . . . . . . . . . . . . . . . . . . . 16 PCB Layout (not in scale). Option nº 2: -24V output voltage . . . . . . . . . . . . . . . . . . . . . . . 16 3/18 List of tables AN2359 AN2359 List of tables Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11. Table 12. 4/18 Proposed converters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 SMPS specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Circuit characterization - VIN = 120VDC 120VDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Circuit characterization - VIN = 320VDC 320VDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Circuit characterization - VIN = 374VDC 374VDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 SMPS specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Experimental results - VIN=120VDC 120VDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Experimental results - VIN=320VDC 320VDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Experimental results - VIN=374VDC 374VDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 AN2359 AN2359 1 VIPerX2 description VIPerX2 description The proposed converters are based on The VIPerX2A family, which is a range of smart power devices with current mode PWM controller, start-up circuit and protections integrated in a monolithic chip using VIPower M0 Technology. The VIPerX2A family includes: ­ VIPer12, with a 0.4A peak drain current limitation and 730V breakdown voltage; ­ VIPer22, with a 0.7A peak drain current limitation and 730V breakdown voltage. The switching frequency is internally fixed at 60kHz by the integrated oscillator of the VIPerX2. The internal control circuit offers the following benefits: ­ Large input voltage range on the V DD pin accommodates changes in supply voltage; ­ Automatic burst mode in low load condition; ­ Overload protection in hiccup mode. The feedback pin FB is sensitive to current and controls the operation of the device. 2 Output voltage selection Two converters with different output voltage are introduced in this paper. The main specifications are listed in Table 1. Table 1. Proposed converters Output 1 Output 2 POUT(MAX) -12V/150mA -5V/300mA 3.3W -24V/100mA -5V/300mA 3.9W As already discussed, VOUT2 is obtained by means of an intermediate tap on the inductor. This imposes, for the two solutions, a different design of the output inductor in terms of turns ratio, i.e. n=1.4 for the ­12V solution, against n=3.8 for the ­24V solution (even if it could be necessary to tune the turn ratio for proper output voltage). Some disadvantage are related to the ­12V solution: ­ The parasitic capacitance effect between the two windings is increased, compared to the second one. This will bring about higher switching losses in turn-on (see Figure 10. and Figure 11.) and, consequently, a worsening in terms of efficiency; ­ A higher voltage diode is needed to supply the VIPer; ­ The peak current is twice higher, giving less output power margin for a given IDLIM. Therefore, a ­24V/-5V solution can be suitably used for all those applications where efficiency and cost are important and, in general, in all the designs where a ­24V output voltage does not impact on the cost of the relays and drivers. 5/18 Application example nº 1 AN2359 AN2359 Instead, the -12V/-5V -12V/-5V solution can be used all those times where it is not possible to change the auxiliary supply voltage. 3 Application example nº 1 The first application example is a 3.3W double output Buck-Boost converter. The specifications are listed in Table 2. The schematic of the circuit is shown in Figure 1. and the component list is shown in Table 3. Table 2. SMPS specifications Specification Value Input voltage range, VIN 88 - 265VAC 265VAC Output voltage VOUT1 -12V Output voltage VOUT2 -5V Maximum output current IOUT1 150mA Maximum output current IOUT2 300mA Maximum output power 3.3W The input voltage can range from 88VAC 88VAC to 265VAC 265VAC. The input section consists in a resistor as a fuse, a single input rectifier diode and an input C-L-C filter. Such a filter provides both DC voltage stabilization and EMI filtering. The CSN-RSN leg across D1 helps the further reducing of the conducted emissions. The regulation feedback is connected to VOUT2 by means of the PNP transistor Q1 and zener diode DZ2, in order to provide an output voltage with tight regulation range (the output precision depends on DZ2 tolerance). VOUT1 is obtained thanks to the turns ratio of the transformer. The output inductor is wound in a TDK drum ferrite core (SRW0913 SRW0913 type), with an intermediate tap for VOUT2. The specifications are the following: L1-3 = 420µH; N1-2 = 70 turns; N2-3 = 62 turns. Optional bleeder resistors, Rb1 and Rb2, can be connected to the outputs in order to improve the regulation. In particular, Rb1 has to be chosen in order to avoid the overvoltage on VOUT1 when VOUT2 is full loaded and VOUT1 is in no load condition. 6/18 AN2359 AN2359 Application example nº 1 Figure 1. Converter schematic Table 3. Component list Reference Value Description RFUSE 22 1/2W , Metallic oxide resistor RSN, R1 1.2K 1/4W , Resistor R2 22 1/2W , Resistor R3 68 1/4W , Resistor Rb1, Rb2 Optional resistor CSN 0.1µF, 400V Polyester capacitor C1, C2 10µF, 400V Electrolytic capacitor C3 10µF, 50V Electrolytic capacitor C4 22nF, 35V Ceramic capacitor C5 0.47µF, 50V Electrolytic capacitor C6 4.7µF, 50V Electrolytic capacitor C7 220µF, 16V Electrolytic capacitor C8 470µF, 16V Electrolytic capacitor D1 Diode 1N4007 1N4007 D2, D3 Diode BA157 BA157 D4, D5 Diode STTH106 STTH106 (ultrafast) DZ1 Diode Zener 6.8V DZ2 Diode Zener 4.3V Q1 PNP transistor BC558 BC558 L1 470µH Axial inductor 7/18 Application example nº 1 Table 3. AN2359 AN2359 Component list (continued) Reference Value Description L2 (Read sec. 5) IC 3.1 STMicroelectronics VIPer22ADIP Experimental results The power supply has been characterized in terms of line and load regulation. The efficiency measurements have been taken using a DC power source and a milliamperometer, in order to have higher accuracy than in AC measurements. In Table 4.,Table 5. and Table 6. the experimental results are shown. It is then possible to observe the efficiency decreases, at same output power, when VOUT2 is more loaded. This can be explained with an increase of the parasitic capacitance effect between the windings. These measurements have been performed without bleeder resistors. Consequently, an overvoltage occurs on VOUT1 when it is in no load condition and VOUT2 is full loaded. This can be avoided adding a 3.3KW resistor as a bleeder, with only a slight reduction of the efficiency. In Figure 2., Figure 3., Figure 4., Figure 5., Figure 6., and Figure 7. typical waveforms at minimum and maximum input voltage are shown. Figure 8. and Figure 9. shows the output ripple voltage at full load at minimum and maximum input voltage. In Figure 10. and Figure 11. turn-on losses measurements are shown in the same previous conditions. It is important to point out that a lot of power is dissipated in turn-on, due to the parasitic capacitance of the inductor. Table 4. Circuit characterization - VIN = 120VDC 120VDC IOUT1 [mA] IOUT2 [mA] VOUT1[V] VOUT2[V] IIN [mA] PIN [W] POUT[W] [%] 0 0 12.00 5.01 1.08 0.129 0 0 0 150 14.73 4.99 9.71 1.16 0.784 67.58 0 300 16.04 4.97 18.33 2.20 1.49 67.70 75 0 10.51 5.00 8.86 1.06 0.788 74.30 75 150 11.15 4.97 17.60 2.11 1.58 74.80 75 300 11.32 4.95 27.10 3.25 2.33 71.70 150 0 10.40 4.99 16.81 2.02 1.56 77.20 150 150 10.95 4.95 26.40 3.17 2.38 75.00 150 300 11.14 4.92 36.60 4.40 3.15 71.50 Table 5. Circuit characterization - VIN = 320VDC 320VDC IOUT1 [mA] IOUT2 [mA] VOUT1[V] VOUT2[V] IIN [mA] PIN [W] POUT[W] [%] 0 11.77 5.04 0.47 0.15 0.00 0.00 0 150 15.56 5.02 3.89 1.24 0.75 60.49 0 300 16.26 5.01 7.25 2.32 1.50 64.78 75 8/18 0 0 10.55 5.02 3.55 1.14 0.79 69.65 AN2359 AN2359 Application example nº 1 Table 5. Circuit characterization - VIN = 320VDC 320VDC IOUT1 [mA] IOUT2 [mA] VOUT1[V] VOUT2[V] IIN [mA] PIN [W] POUT[W] [%] 75 150 11.23 5.01 7.01 2.24 1.59 71.05 75 300 11.37 4.99 10.53 3.37 2.35 69.73 150 0 10.4 5.01 6.7 2.14 1.56 72.76 150 150 11.01 5 10.38 3.32 2.40 72.30 150 300 12.21 4.98 14.44 4.62 3.33 71.97 Table 6. Circuit characterization - VIN = 374VDC 374VDC IOUT1 [mA] IOUT2 [mA] VOUT1[V] VOUT2[V] IIN [mA] PIN [W] POUT[W] [%] 0 11.74 5.06 0.44 0.16 0.00 0.00 0 150 15.77 5.02 3.39 1.27 0.75 59.39 0 300 16.51 5 6.38 2.39 1.50 62.86 75 0 10.54 5.02 3.09 1.16 0.79 68.40 75 150 11.26 5.01 6.18 2.31 1.60 69.05 75 300 11.41 5 9.36 3.50 2.36 67.29 150 0 10.4 5.01 5.92 2.21 1.56 70.46 150 150 11.05 5.01 9.26 3.46 2.41 69.56 150 Figure 2. 0 300 11.2 4.98 12.74 4.76 3.17 66.61 Typical waveforms at 88VAC 88VAC: open load Figure 3. Typical waveforms at 88VAC 88VAC: full load Ch1 Freq - 2.38kHz Ch1 Freq - 59.61kHz Ch2 Max - 228mA Ch2 Max - 572mA 9/18 Application example nº 1 Figure 4. AN2359 AN2359 Typical waveforms at 265VAC 265VAC: open Figure 5. load Typical waveforms at 265VAC 265VAC: full load Ch1 Freq - 2.39kHz Ch2 Max - 428mA Figure 6. Ch1 Freq - 59.65kHz Ch2 Max - 532mA Commutation at full load: 88VAC 88VAC Figure 7. Commutation at full load: 265VAC 265VAC - 530 mA Ch 2 M ax -5 62 m A Ch1 Max - 366V C h2 Ma x Ch1 Freq - 103V Figure 8. Output ripple voltage at full load: 88VAC 88VAC Ch1 Pk-Pk - 90mV Ch3 Pk-Pk - 80mV 10/18 Figure 9. Output ripple voltage at full load: 265VAC 265VAC Ch1 Pk-Pk - 108mV Ch3 Pk-Pk - 82mV AN2359 AN2359 Application example nº 1 Figure 10. Turn on losses measurement at full Figure 11. Turn on losses measurement at full load: 88VAC 88VAC load: 265VAC 265VAC M1 Area 2.92µWs M1 Area 10.07µWs 3.2 Thermal measurements In this application, the main thermal issues are related to parasitic capacitance effects that can lead to higher power dissipation in the device and then higher working temperature. In order to evaluate the case temperature of the VIPer in the entire input voltage range, a thermal mapping by means of an IR Camera was done at ambient temperature and full load. In Figure 12. and Figure 13. the thermal profile of the device at minimum and maximum input voltage range respectively is shown. It is important to highlight that at low line the conduction losses are predominant, instead at high input voltage the switch losses became not negligible, due to parasitic capacitance of the inductor. This is point out in Figure 14. Figure 12. VIPer22A Thermal profile: at VIN= 88VAC 88VAC TCASE(MAX)=53.3°C Figure 13. VIPer22A Thermal profile: at VIN= 265VAC 265VAC TCASE(MAX)=67.3°C 11/18 Application example nº 2 AN2359 AN2359 Figure 14. VIPer22A temperature at maximum load 4 Application example nº 2 In this second example, the Buck-Boost is modified in order to have ­24V/-5Voutputs voltages in a 4W application. In Table 7. the main specifications of the power supply are listed. The schematic of the circuit and the component list are shown in Figure 15. and in Table 8. respectively. Table 7. SMPS specifications Specification Value Input voltage range, VIN 88 - 265VAC 265VAC Output voltage VOUT1 -24V Output voltage VOUT2 -5V Maximum output current IOUT1 100mA Maximum output current IOUT2 300mA Maximum output power 4W The ­24V output voltage allows to supply the VIPer directly from the feedback path, saving the cost of a high voltage diode. Even in this case, the feedback regulation is connected to VOUT2 by means of Q1 transistor and DZ1 zener diode. The output inductor, with intermediate tap for VOUT2, is provided by PULSE (PFM0250 PFM0250 type) with the following features: N1-3 / N2-3 = 3.81 ± 2%; R1-2 = 560mW (max); 12/18 L1-3 = 510µH ±10%; R2-3 260W (max). AN2359 AN2359 Application example nº 2 Also bleeder resistors or zener diodes may be mandatory at no load in order to improve the regulation and avoid output overvoltage. Figure 15. Converter schematic Table 8. Component list Reference Value Description RFUSE 22 1/2W , Metallic oxide resistor RSN, R1 1.2K 1/4W , Resistor R2 22 1/4W , Resistor R3 100 1/4W , Resistor Rb1, Rb2 Optional resistor CSN 0.1µF, 400V Polyester capacitor C1, C2 10µF, 400V Electrolytic capacitor C3 33µF, 25V Electrolytic capacitor C4 47nF, 35V Ceramic capacitor C6 22µF, 16V Electrolytic capacitor C7 470µF, 25V Electrolytic capacitor C8 100µF, 16V Electrolytic capacitor D1 Diode 1N4007 1N4007 D2, D4, D5 Diode BYT11-400 BYT11-400 (ultrafast) DZ1 Diode Zener 18V DZ2 Diode Zener 4.3V Q1 PNP transistor BC327 BC327 L1 470µH Axial inductor 13/18 Application example nº 2 Table 8. AN2359 AN2359 Component list (continued) Reference Value Description L2 (Read sec. 6) Pulse PFM0250 PFM0250 IC 4.1 STMicroelectronics Experimental results In Table 9., Table 10. and Table 11. the measures performed on the proposed converter are listed. In Figure 16. and Figure 17. typical waveforms at 300VDC 300VDC are shown. The converter performs well in terms of line and load regulation. The ­5V output shows a ±5% of precision. VOUT1, obtained by means of the turns ratio of the inductor, shows good performance too, even if an overvoltage occurs on VOUT1 when it is in no load condition and VOUT2 is full loaded. This can be avoided connecting an appropriate bleeder resistor on VOUT1. The efficiency measurements show a better behavior compared to the ­12V solution. This can be explained because, in this configuration, the turn-on losses are lower compared to the ­12V solution. Table 9. Experimental results - VIN=120VDC 120VDC IOUT1[mA] IOUT2[mA] VOUT1[V] VOUT2[V] IIN[mA] PIN[W] POUT[W] [%] 0 0 24.09 5.096 0.986 0.1972 0 0.00 10 30 23.87 5.098 3.643 0.7286 0.39164 53.75 50 150 23.97 5.087 13.33 2.666 1.96155 73.58 80 240 24.05 5.075 20.5 4.1 3.142 76.63 100 300 24.06 5.069 25.68 5.136 3.9267 76.45 0 300 41.54 5.02 12.74 2.55 1.51 59.11 100 0 21.82 5.083 13.74 2.75 2.18 79.40 Table 10. Experimental results - VIN=320VDC 320VDC IOUT1[mA] IOUT2[mA] VOUT1[V] VOUT2[V] IIN[mA] PIN[W] POUT[W] [%] 0 24.1 5.098 0.666 0.20 0.00 0.00 10 30 23.9 5.094 2.435 0.73 0.39 53.64 50 150 23.96 5.091 9.182 2.75 1.96 71.21 80 240 24.03 5.079 13.85 4.16 3.14 75.60 100 300 24.03 5.068 17.17 5.15 3.92 76.17 0 300 41.14 5.025 8.684 2.61 1.51 57.87 100 14/18 0 0 21.89 5.096 9.41 2.82 2.19 77.54 AN2359 AN2359 Layout considerations Table 11. Experimental results - VIN=374VDC 374VDC IOUT1[mA] IOUT2[mA] VOUT1[V] VOUT2[V] IIN[mA] PIN[W] POUT[W] [%] 0 0 24.16 5.098 0.513 0.21 0.00 0.00 10 30 23.99 5.094 1.852 0.74 0.39 53.01 50 150 24 5.094 7.04 2.82 1.96 69.75 80 240 24.03 5.085 10.66 4.26 3.14 73.71 100 300 24.028 5.071 13.14 5.26 3.92 74.66 0 300 41 5.03 6.68 2.67 1.51 56.47 100 0 21.93 5.1 7.221 2.89 2.19 75.92 Figure 16. Typical waveforms at 300VDC 300VDC and full load: commutation 5 Figure 17. Typical waveforms at 300VDC 300VDC and full load: detail Layout considerations A proper PCB layout is essential for correct operation of any switch-mode converter and the same basic rules have to be taken into account in order to optimize the current path, especially in high current path routing. Since EMI issues are related to layout, the current loop area has to be minimized. Moreover, the control ground path has to be separated from power ground, in order to avoid any noise interference between the control section and the power section. All the traces carrying high currents have to be as short as possible, in order to minimize the resistive and inductive effect. A particular care has to be taken into account regarding the optimal routing of the input EMI filter path and the correct placement of any single component (L1 ­R1 very close to input bulk capacitors, trace as short as possible.). 15/18 Layout considerations AN2359 AN2359 Finally, dissipating copper area on the VIPer drain and diodes pins have to be provided, in order to increase the power dissipation capability and, consequently, reduce the devices temperature. The circuit layout is shown in figure 12 for the ­12V configuration and in figure 13 for the ­ 24V configuration. The PCB is the same and includes the options for the two configurations. Figure 18. PCB Layout (not in scale). Option nº 1: -12V output voltage Figure 19. PCB Layout (not in scale). Option nº 2: -24V output voltage 16/18 AN2359 AN2359 6 Conclusions Conclusions Two low cost double outputs Buck-Boost converters have been proposed based on STMicroelectronics VIPer22A. Thanks to the regulation feedback connected to ­5V output, the converters can be suitably used to supply a microcontroller or applications where a high output voltage tolerance is required. Instead, the -12V or-24V output voltage, achieved by the output inductor turns ratio, can be used for the auxiliary circuits where a lower tolerance can be accepted. In particular, the ­24V option can be preferred because it guarantees a higher efficiency (due to lower turn- on losses) and allows to save the cost of a high voltage diode compared to the ­12V solution. On the other side, the ­12V solution has to be used in many applications when it is not possible to change the auxiliary supply voltage from ­12V to ­24V. The same topology can be used for lower power range, replacing the VIPer22 with the VIPer12. In this case the device can deliver up to about 2.2W. 7 Revision history Table 12. Revision history Date Revision 04-Dec-2006 1 Changes Initial release 17/18 AN2359 AN2359 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries ("ST") reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST's terms and conditions of sale. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. 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