EVL90WADP-LLCSR

AN3014 Application note 19 V, 90 W resonant converter with synchronous rectification using L6563H, L6599A and SRK2000A Claudio Spini Introduction This application note describes the characteristics and the features of a 90 W demonstration board (EVL90WADP-LLCSR), tailored to specifications for a typical high-end portable computer power supply. A peculiarity of this SMPS design is the very high efficiency compliant with ENERGY STAR® eligibility criteria (EPA rev. 2.0 EPS). One of the key factors in achieving this result is the SRK2000A. This synchronous rectification driver for LLC resonant converters allows significantly reduced secondary-side losses. Thanks to this improvement, secondary-side heatsinks, which are typically needed for this power range, can be dramatically reduced or even removed. Figure 1. EVL90WADP-LLCSR: 90 W adapter demonstration board $0Y June 2017 DocID16064 Rev 3 1/29 www.st.com 29 Contents AN3014 Contents 1 Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . . . 5 2 Efficiency measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3 Harmonic content measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4 Functional check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5 Thermal map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6 Conducted emission pre-compliance test . . . . . . . . . . . . . . . . . . . . . . 18 7 Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 8 PFC coil specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 9 Transformer specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2/29 DocID16064 Rev 3 AN3014 List of tables List of tables Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Overall efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Efficiency comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Light load efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Thermal map reference points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 EVL90WADP-LLCSR demonstration board bill of material . . . . . . . . . . . . . . . . . . . . . . . . 19 PFC coil winding data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Transformer winding data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 DocID16064 Rev 3 3/29 29 List of figures AN3014 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. Figure 20. Figure 21. Figure 22. Figure 23. 4/29 EVL90WADP-LLCSR: 90 W adapter demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . 1 Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Light load efficiency diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Compliance to EN61000-3-2 at 230 Vac - 50 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . 12 Compliance to JEITA-MITI at 100 Vac - 50 Hz, full load. . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Resonant stage oscillator at 230 V - 50 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Resonant stage waveforms at 230 V - 50 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Secondary waveforms at 230 V - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Startup sequencing at 230 V - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 No load operation at 230 V - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 No load operation - detail at 230 V - 50 Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Transition full load to no load at 265 Vac - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Transition no load to full load at 265 Vac - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Short-circuit at full load and 115 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Short-circuit detail at full load and 115 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Thermal map at 115 Vac - 60 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Thermal map at 230 Vac - 50 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 CE average measurement at 115 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 CE average measurement at 230 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 PFC coil electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 PFC coil mechanical aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Transformer electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Transformer overall drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 DocID16064 Rev 3 AN3014 1 Main characteristics and circuit description Main characteristics and circuit description The main features of the SMPS are:  Universal input mains range: 90 264 Vac, frequency 45  65 Hz  Output voltage: 19 V at 4.75 A continuous operation  Mains harmonics: according to EN61000-3-2 class-D or JEITA-MITI class-D  Standby mains consumption: < 0.26 W at 230 Vac  Efficiency at nominal load: > 92% at 115 Vac  EMI: according to EN55022-class-B  Safety: according to EN60950  Dimensions: 65 x 155 mm, 25 mm maximum component height  PCB: double-sided, 70 µm, FR-4, mixed PTH/SMT The circuit is composed of two stages: a front-end PFC using the L6563H, and a LLC resonant converter based on the L6599A. The SRK2000A controls the synchronous rectification on the secondary side. The PFC stage works as a preregulator and powers the resonant stage with a constant voltage of 400 V. The downstream converter operates only if the PFC is on and regulating. In this way, the resonant stage can be optimized for a narrow input voltage range. Startup sequence As indicated previously, the PFC acts as master and the resonant stage can operate only if the PFC output is delivering the nominal output voltage. Therefore the circuit is designed so that at startup the PFC starts first, then the downstream converter turns on. Initially, the L6563H is supplied by the integrated high voltage startup circuit, but as soon as the PFC starts switching, a charge pump connected to the PFC inductor supplies both the PFC and resonant controllers. Once both stages have been activated, the controllers are supplied also by the auxiliary winding of the resonant transformer, assuring correct supply voltage even during standby operation. Because the L6563H integrated HV startup circuit is turned off and therefore is not dissipative during normal operation, it significantly contributes to the reduction of power consumption when the power supply operates at light load, in accordance with current world-wide standby consumption standards. Brownout protection Brownout protection prevents the circuit from working with abnormal mains levels. It is easily achieved using the RUN pin (pin12) of the L6563H. This pin is connected through a resistor divider to the VFF pin (pin 5), which provides the mains voltage peak value information. An internal comparator enables the IC operations if the mains level is correct, within the nominal limits. At startup, if the input voltage is below 90 Vac (typ), circuit operations are inhibited. The L6599A has similar protection on the LINE pin (pin 7). It is used to prevent the resonant converter from working with too low an input voltage, which can cause incorrect capacitive mode operation. If the bulk voltage (PFC output) is below 380 V, the resonant startup is not allowed. The L6599A internal comparator has a hysteresis which allows the turn-on and turn-off voltage to be set independently. The turn-off threshold has been set to 300 V in DocID16064 Rev 3 5/29 29 Main characteristics and circuit description AN3014 order to avoid capacitive mode operation, but to allow the resonant stage to operate even in case of mains sag and consequent PFC output dip. Fast voltage feed-forward The voltage on the L6563H VFF pin (pin 5) is the peak value of the voltage on the MULT pin (pin 3). The RC network (R15+R26, C12) connected to VFF completes the peak-holding circuit. This signal is necessary to derive RMS input voltage information to compensate the loop gain, which is mains voltage dependent. Generally speaking, if the time constant is too small, the voltage generated is affected by a considerable amount of ripple at twice the mains frequency, thus causing distortion of the current reference (resulting in high THD and poor PF). If the time constant is too large, there is a considerable delay in setting the right amount of feed-forward, resulting in excessive overshoot or undershoot of the preregulator's output voltage in response to large line voltage changes. To overcome this issue, the L6563H implements the new fast voltage feed-forward function. As soon as the voltage on the VFF pin decreases to a set threshold (40 mV typically), a mains dip is assumed and an internal switch rapidly discharges the VFF capacitor via a 10k resistor. Thanks to this feature, it is possible to set an RC circuit with a long time constant, assuring a low THD and maintaining a fast response to mains dip. Resonant power stage The downstream converter employs ST’s L6599A, which incorporates all the functions necessary to properly control the resonant converter with a 50% fixed duty cycle and works with a variable frequency. The transformer uses the integrated magnetic approach, incorporating a resonant series inductor. Thus, no additional external coil is needed for the resonance. The transformer configuration chosen for the secondary winding is center tap. On the secondary side, the output rectification is controlled by the SRK2000A, an SR driver dedicated to LLC resonant topology. A small LC filter has been added on the output, filtering the high-frequency ripple. D15, R56, R62, R65, R66, Q5 and Q6 implement an output voltage “fast discharge” circuit which quickly discharges the output capacitors when the converter is turned off. It has been implemented to quickly decrease the residual output voltage after the converter is turned off at no load. Output voltage feedback loop The feedback loop is implemented by means of a typical circuit using a TL431 to modulate the current in the optocoupler diode. On the primary side, R34 - connecting the RFMIN pin (pin 4) to the optocoupler phototransistor - closes the feedback loop and its value sets the maximum switching frequency at about 130 kHz. This value has been chosen to limit the switching losses at light load operation. R31, which connects the same pin to ground, sets the minimum switching frequency. The R-C series (R44 and C18) sets both the soft-start maximum frequency and duration. 6/29 DocID16064 Rev 3 AN3014 Main characteristics and circuit description L6599A overload and short-circuit protection The current into the primary winding is sensed by the lossless circuit R41, C27, D11, D10, R39, and C25 and is fed to the ISEN pin (pin 6). In case of overcurrent, the voltage on the pin passes an internal threshold (0.8 V), triggering a protection sequence. The capacitor (C45) connected to the DELAY pin (pin 2) is charged by an internal 150-µA current generator and is slowly discharged by the external resistor (R24). If the voltage on the pin reaches 2 V, the soft-start capacitor is completely discharged so that the switching frequency is pushed to its maximum value. As the voltage on the pin exceeds 3.5 V, the IC stops switching and the internal generator is turned off, so that the voltage on the pin decays due to the external resistor. The IC is soft-restarted as the voltage drops below 0.3 V. In this way, under short-circuit conditions, the converter works intermittently with very low input average power. Overvoltage and open loop protection Both the PFC and resonant circuit stages are equipped with their own overvoltage protection. The PFC controller L6563H monitors its output voltage via the resistor divider connected to a dedicated pin (PFC_OK, pin 7), protecting the circuit in case of loop failures, disconnection or deviation from the nominal value of the feedback loop divider. If the voltage on pin #7 exceeds 2.5 V the IC stops switching and restarts as the voltage on the pin falls below 2.4 V, preventing the output voltage becoming excessive in case of transient due to the slow response of the error amplifier. However, if contemporaneously the voltage of the INV pin falls below 1.66 V (typ.), a feedback failure is assumed. In this case the PFC_OK circuitry latches the L6563H operations and, by means of the PWM_LATCH pin (pin 8) it latches the L6599A as well, via the DIS pin (pin 8). The converter is kept latched by the L6563H HV circuit which supplies the IC, charging the VCC capacitor periodically. To resume converter operation, mains restart is necessary. The DIS pin is used to protect also the resonant stage against overvoltage. The Zener diode D8 detects the auxiliary voltage, which is proportional to the output voltage. In case of loop failure it conducts and voltage on the DIS pin exceeds the internal threshold, and latches off the device. L6563H operation is also stopped by the PFC_STOP pin. Secondary-side synchronous rectification with the SRK2000A The SRK2000A core function is to switch on each synchronous rectifier MOSFET whenever the corresponding transformer half-winding starts conducting (i.e. when the MOSFET body diode starts conducting), and then to switch it off when the current flowing through it approaches zero. For this purpose, the IC is equipped with two pins (DVS1 and DVS2) capable of sensing the MOSFET drain voltage level. Standby power saving The board has a burst-mode function implemented, allowing power saving during light load operation. The L6599A STBY pin (pin 5) senses the optocoupler’s collector voltage, which is related to the feedback control. This signal is compared to an internal reference (1.24 V). If the voltage on the pin is lower than the reference, the IC enters an idle state and its quiescent current is reduced. As the voltage exceeds the reference by 50 mV, the controller restarts the switching. The burst-mode operation load threshold can be programmed by properly choosing the resistor connecting the optocoupler to the RFMIN pin (R34). On this board, the controller operates in burst-mode if the load falls below ~10 W. DocID16064 Rev 3 7/29 29 Main characteristics and circuit description AN3014 The L6563H implements its own burst-mode function. If the COMP voltage falls below 2.5 V, the IC stops switching, causing an output voltage drop. As a consequence, the COMP voltage rise again and the IC starts switching again. In order to achieve better load transient response, the PFC burst-mode operation is partially forced by the resonant converter: as soon as the L6599A stops switching due to load drops, its PFC_STOP pin pulls down the L6563H's PFC_OK pin, disabling PFC switching. Thanks to this simple circuit, the PFC is forced into an idle state when the resonant stage is not switching, and rapidly wakes up when the downstream converter restarts switching. This solution prevents significant drop of the bulk voltage in case of abrupt load rising. 8/29 DocID16064 Rev 3 3 
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O' % #;7$ $ AN3014 Main characteristics and circuit description Figure 2. Electrical diagram 9/29 29 Efficiency measurement 2 AN3014 Efficiency measurement EPA rev. 2.0 external power supply compliance verification Table 1 shows the no-load consumption and overall efficiency, measured at the nominal mains voltages. At 115 Vac the average efficiency is 91.27%, while at 230 Vac it is 92.22%. Both values are much higher than the 87% required by the EPA rev 2.0 external power supply limits. Even at no-load, the board performances are superior: maximum no-load consumption at nominal mains voltage is 260 mW only. This value is significantly lower than the limit imposed by the ENERGY STAR® program, which is 500 mW. Table 1. Overall efficiency 230 V-50 Hz Test 115 V-60 Hz Vout Iout Pout Pin Eff. Vout Iout Pout Pin Eff. [V] [mA] [W] [W] [%] [V] [mA] [W] [W] [%] No load 18.98 0.00 0.00 0.26 - 18.98 0.00 0.00 0.23 - 25% load eff. 18.97 1187 22.52 25.46 88.45% 18.97 1187 22.51 25.41 88.57% 50% load eff. 18.95 2375 45.01 48.70 92.42% 18.95 2374 44.99 49.03 91.77% 75% load eff. 18.94 3565 67.52 71.96 93.82% 18.94 3565 67.50 73.06 92.38% 100% load eff. 18.92 4756 89.99 95.54 94.19% 18.92 4758 90.02 97.48 92.34% Average eff. - 92.22% - 91.27% Efficiency comparison between diode rectification and synchronous rectification In Table 2, the efficiency of two different designs are compared. One is the EVL90WADPLLCSR board, and the other is an identical board but with diode rectification (two STPS10L60 devices). In this way, a direct indication of the efficiency improvement obtained with the new synchronous rectification solution is obtained. Table 2. Efficiency comparison 230 V - 50 Hz Test 115 V - 60 Hz Eff. with diodes Eff. with SRK2000A Variation Eff. with diodes Eff. with SRK2000A Variation 25% load eff. 87.49% 88.45% 0.96% 88.24% 88.57% 0.33% 50% load eff. 91.52% 92.42% 0.90% 90.85% 91.77% 0.91% 75% load eff. 92.58% 93.82% 1.24% 91.16% 92.38% 1.23% 100% load eff. 92.84% 94.19% 1.35% 91.00% 92.34% 1.34% Average eff. 91.11% 92.22% 1.11% 90.31% 91.27% 0.95% 10/29 DocID16064 Rev 3 AN3014 Efficiency measurement Light load operation efficiency Measurement results are reported in Table 3 below and plotted in Figure 3. As shown, efficiency is better than 68% even for very light loads, such as 1 W. Table 3. Light load efficiency 230 V - 50 Hz Test 115 V - 60 Hz Vout Iout Pout Pin Eff. Vout Iout Pout Pin Eff. [V] [mA] [W] [W] [%] [V] [mA] [W] [W] [%] 0.25 W 18.97 13.2 0.250 0.610 41.05% 18.97 13.2 0.250 0.590 42.45% 0.5 W 18.97 26.4 0.501 0.877 57.18% 18.97 26.4 0.501 0.870 57.57% 1.0 W 18.97 52.7 0.999 1.467 68.13% 18.97 52.7 0.999 1.457 68.60% 1.5 W 18.98 79.0 1.499 2.160 69.41% 18.97 79.2 1.503 2.134 70.41% 2.0 W 18.97 105.5 2.002 2.822 70.93% 18.97 105.5 2.002 2.895 69.15% 2.5 W 18.97 131.8 2.500 3.558 70.27% 18.98 131.8 2.501 3.711 67.38% 3.0W 18.98 158.3 3.004 4.110 73.09% 18.97 158.3 3.002 4.230 70.97% 3.5 W 18.97 184.5 3.501 4.660 75.13% 18.97 184.5 3.501 4.637 75.49% 4.0 W 18.97 210.8 3.999 5.256 76.08% 18.97 210.8 3.999 5.234 76.40% 4.5 W 18.97 237.3 4.502 5.840 77.08% 18.97 237.3 4.502 5.830 77.22% 5.0 W 18.97 263.6 5.000 6.450 77.52% 18.97 263.6 5.001 6.420 77.89% Figure 3. Light load efficiency diagram   (IILFLHQF\      9+]  9+]              2XWSXWSRZHU>:@ $0Y DocID16064 Rev 3 11/29 29 Harmonic content measurement 3 AN3014 Harmonic content measurement The board has been tested according to the European standard EN61000-3-2 class-D and Japanese standard JEITA-MITI Class-D, at both nominal input voltage mains. As reported in graphs that follow, the circuit is capable of reducing the harmonics well below the limits of both regulations. Figure 4. Compliance to EN61000-3-2 at 230 Vac - 50 Hz, full load 0HDVXUHGYDOXH Figure 5. Compliance to JEITA-MITI at 100 Vac - 50 Hz, full load 0HDVXUHGYDOXH (1&ODVV'OLPLWV -(,7$0,7,&ODVV'OLPLWV   +DUPRQLF&XUUHQW>$@ +DUPRQLF&XUUHQW>$@                              7+' 3)                     +DUPRQLF2UGHU>Q@ +DUPRQLF2UGHU>Q@ $0Y 7+' 3)  $0Y At the bottom of the diagrams, the total harmonic distortion and power factor measurements are also reported. The values in all conditions provide a clear overview of the correct functionality of the PFC. 12/29 DocID16064 Rev 3 AN3014 4 Functional check Functional check Figure 6 and Figure 7 are waveforms relevant to the resonant stage during steady state operation. The selected switching frequency is approximately 100 kHz in order to achieve a good trade-off between transformer losses and dimensions. The converter operates above the resonance frequency. Figure 7 shows the resonant ZVS operation. Both MOSFETs are turned on when resonant current is flowing through their body diodes and the drain-source voltage is zero. Figure 6. Resonant stage oscillator at 230 V - 50 Hz - full load &+ +%YROWDJH &+ &)SLQYROWDJH &+ 9FF &+ 5HVWDQNFXUUHQW $0Y Figure 7. Resonant stage waveforms at 230 V - 50 Hz - full load &+ +%YROWDJH  &+ /9)(7JDWH &+ +9)(7JDWH &+ 5HVWDQNFXUUHQW $0Y In Figure 8, typical waveforms relevant to the secondary side are shown. It can be noted that the rectifier MOSFETs are switched on and off according to the current flowing through them. Figure 9 shows the waveforms during startup at 90 Vac and full load. Here, the sequence of the two stages can be noted: at power-on the L6563H and L6599A VCC voltages increase up to the turn-on thresholds of the two ICs. The PFC starts and its output voltage increases from the mains rectified voltage to its nominal value. In the meantime, the L6599A is kept inactive by the LINE pin (pin 7) until the PFC voltage reaches the set threshold. Then the resonant starts operating and the output voltage reaches the nominal level. DocID16064 Rev 3 13/29 29 Functional check AN3014 Figure 8. Secondary waveforms at 230 V - 50 Hz &+ 4JDWH &+ 4JDWH &+ 4FXUUHQW &+ 4FXUUHQW $0Y Figure 9. Startup sequencing at 230 V - 50 Hz &+ 4JDWH &+ 4JDWH &+ 4FXUUHQW &+ 4FXUUHQW $0Y Standby and no-load operation In Figure 10 and Figure 11, some burst-mode waveforms are displayed. As illustrated, both the L6599A and L6563H operate in burst-mode. In Figure 11 it can be observed that the PFC and LLC bursts are synchronized. Figure 10. No load operation at 230 V - 50 Hz &+ +%YROWDJH &+ 3)&JDWHYROWDJH &+ 67%