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issue: Power Semiconductors Contributing in Energy Management ABSTRACT Electronic Devices Business Group, Fuji Electric Co., Ltd. 㾙Sales Group, Fuji Electric Co., Ltd. 245 1. Introduction Switching power supply products, which are used in various types of electronic equipment, are rapidly being improved in terms of ef fi ciency, noise reduction and low pro fi le to meet the demands for energy ef- fi ciency and space saving. An LLC current resonant power supply is characterized by its use of high-ef fi - ciency, low-noise soft switching technology and low- profi le leakage transformer structure. These charac- teristics facilitate ef fi ciency improvement, noise reduc- tion and pro fi le lowering and make it suitable for use as a power supply of 100 to 500 W, which is a medium capacity range for a switching power supply. The LLC current resonant power supply, however, is prone to a switching shoot-through phenomenon* 1 during a start- up, heavy load conditions or low input voltage condi- tions. The power supply has problems including a breakdown of a power metal-oxide-semiconductor fi eld- effect transistor (MOSFET) due to this phenomenon and effi ciency degradation with a light load due to an excitation current, and these factors limited its scope of application. In order to solve these problems, Fuji Electric commercialized “FA5760N,” an LLC current reso- nant control IC that uses its unique new control sys- tem. FA5760N is an LLC resonant converter that eliminates the need for a PFC converter and dedicated CHEN Jian YAMADAYA Masayuki SHIROYAMA Hironobu㾙 2nd Generation LLC Current Resonant Control IC, “FA6A00N Series” LLC current resonant power supply, which is characterized by soft switching, resonance control with a duty ratio of 50% and leakage transformer structure, is suitable for effi ciency improvement, noise reduction and profi le lower- ing in switching power supply. Fuji Electric has developed the 2nd generation “FA6A00N Series,” which inherits the characteristics of the 1st generation LLC current resonant control IC, “FA5760N,” and is enhanced with lower standby power and improved protective functions. It integrates the world’s fi rst high-precision secondary side over-load pro- tection function while further reducing the standby power by approximately 20%. For the over-current protection function, the delay time can be externally adjusted. standby converter and allows a power management system con fi guration that offers high ef fi ciency, low standby power and compactness. This has expanded the scope of its application such that it is adopted to a power supply of about 50 W without a PFC converter. Fuji Electric has recently developed the “FA6A00N Series,” the 2nd-generation LLC current resonant con- trol IC. With the characteristics of the 1st-generation LLC current resonant control IC “FA5760N” inherited, it is enhanced with a lower standby power, improved protective functions, higher quality and lower system cost and offers a higher degree of design freedom. 2. Overview of Product Figure 1 shows the external appearance of the FA6A00N Series and Fig 2 the block diagram. Table 1 lists the major ratings, Table 2 the major functions and Table 3 shows the product lineup. The following outlines the LLC current resonant control IC of the FA6A00N Series. *1: Switching shoot-through phenomenon: a phenomenon in which, when a current fl ows through the body diode of one power MOSFET in a bridge switching circuit, the opposing power MOSFET turns on to instantaneously generate a large current. Fig.1 “FA6A00N Series”
246 FUJI ELECTRIC REVIEW vol.59 no.4 2013 (a) Control circuit with 3.3 V, 5 V and 30 V break- down voltage for controlling the LLC current resonant circuit (b) Driver circuit with 630 V breakdown voltage capable of directly driving the high side and low side switching devices in the half bridge circuit (c) Built-in 600 V breakdown voltage start-up de- vice realizing IC start-up with low power con- sumption (d) JEDEC-compliant 16-pin small outline package The high side and low side outputs alternately op- erate with a high-precision duty cycle of 50% and the operating frequency range is 38 to 350 kHz. 3. Features
3.1 Low power dissipation burst control
FA5760N, the 1st-generation product, used the VCC and CS terminals for hysteresis burst control and achieved a world-class low standby power without the standby converter. The FA6A00N Series, which is the 2nd generation, is additionally provided with burst control optimization to further reduce the standby power by approximately 20% from FA5760N. The LLC current resonant control has a high side Table 1 Major ratings Item Rated value High side power supply voltage to ground –0.3 to + 630 V High side power supply voltage (VBS) –0.3 to + 30 V Low side power supply voltage (VCC) –0.3 to + 30 V VH terminal input voltage –0.3 to + 600 V Maximum allowable offset power supply voltage dv/dt ±50 kV/ μs (max.) Total loss 0.83 W Operating junction temperature –40 to +150 °C LO GND VB HO VS BO /PGS FB CS Regu- lator BO + BOPINP Intemal Supply UVLO VCC VH STB MODE Start-up circuit X-Cap discharge VH voltage detection circuit VCC_UVLO UVLO BOP VHOVP Standby control circuit Msstb State control circuit SmodeMstb High side driver High side driver High side control circuit Low side driver Low side driver VCC HO control LO control Protection circuit Continuous Protection Pulse-by- pulse protection circuit Pulse-by- pulse Protection Control circuit Oscillator Soft start control circuit Standby control circuit OLP OCP VHOVP UVLO BOP BOPINP on_trg off_trg Continuous protection FB CS DTadj FB CS Pulse by pulse protection Mstb Msstb VCC Smode Mstb Msstb CS Control turn-off Self- adjusting dead time VW OLP detection circuit SmodeMstb FTO Dadj VW_OLP IS VW Fig.2 “FA6A00N Series” block diagram Table 2 Major functions and terminals Function Terminal (No.) Start-up circuit VH (1), VCC (10) Low voltage malfunction prevention circuit VCC (10), VB (16) State setting function MODE (7) X-Cap discharge function VH (1) Fixed brown-in/brown-out VH (1) Variable brown-in/brown-out BO (3) Overvoltage protection VH (1), VCC (10) Over-current protection with variable delay time IS (8), MODE (7) Overload protection VW (9), FB (4) Overheat protection Integrated External latch signal input MODE (7) Forced turn-off function VW (9), IS (8) Automatic dead time adjustment function VW (9) High-precision overload protection function VW (9) Soft start function CS (5) Low standby power operation mode VCC (10), CS (5), VH (1) Power Good signal PGS (3) Table 3 Product lineup Product name Terminal 3 Overload protection Over-current protection FA6A00N PGS terminal Auto-restart Latch stop FA6A01N PGS terminal Auto-restart Auto-restart FA6A10N BO terminal Auto-restart Auto-restart FA6A11N BO terminal Latch stop Latch stop
2472nd Generation LLC Current Resonant Control IC, “FA6A00N Series” issue: Power Semiconductors Contributing in Energy Management and low side duty cycle of 50% and controls the gain by the switching frequency. Figure 3 shows the current resonant gain diagram. The frequency variation range is narrow in principle during normal operation and widened during burst operation. Figure 4 shows the frequency during burst opera- tion. The high frequency region (1) is an invalid region in which the gain is low and switching cannot trans- fer energy. In the low frequency region (3), the gain is high and excitation current is large, which makes energy transfer ineffi cient; hence there is a low conver- sion effi ciency. With the FA6A00N Series, the invalid region and the region with low conversion ef fi ciency have been reduced to widen the region with high con- version effi ciency (2), resulting in successful reduction of standby power. Audible noise has also been sup- pressed.
3.2 High-precision overload protection function
The 1st-generation product FA5760N used the pri- mary side auxiliary winding P2 (see Fig. 5 ) to supply power to the VCC terminal and realized hard switch- ing protection and shoot-through current prevention. The FA6A00N Series, which is the 2nd generation, uses this auxiliary winding to integrate the high-pre- cision overload protection function for the fi rst time in the world while inheriting the functions of FA5760N. The overload protection, which is intended for protecting the power management system, is a func- tion that stops switching when a certain delay time has elapsed after a load increases to approximately 1.5 times the rated load. Degradation of the preci- sion of this function causes insuf fi cient output power or failure to limit the output power, thus the overload protection cannot perform adequately. In addition, the overload protection level must be maintained within a certain range (about ± 20%) even if an input voltage varies in a wide range. Figure 6 shows the circuit confi guration of the high- precision overload protection function of the FA6A00N Series. The auxiliary winding voltage is detected by the resistor-divided voltage, V W voltage. The recom- mended precision of this voltage-dividing resistor is ± 1%. The V W voltage exceeding the threshold voltage Volpvw is recognized as an overload state, and when the overload state continues for 76.8 ms, switching is stopped. In order to improve the detection precision, variation of V olpvw has been specifi ed to be within ± 3%, which is highly precise. The commercialized versions are the auto-restart version, which restarts when the switching stop time has reached 550 ms, and the latch stop version that does not restart. Figure 7 shows a waveform during overload pro- tection operation. In overload protection operation, switching is suspended and the output voltage drops along with an energy transfer stop. Figure 8 shows how the overload protection oper- ating power depends on the input voltage. FA5760N provides overload protection with general resonant current detection. With this method, the overload Range of frequency variation during normal operation Range of frequency variation during burst operation Gain Frequency (kHz) 50 100 150 200 Fig.3 Current resonant gain diagram Frequency Low High FA5760N FA6A00N Series Invalid region Region with high conversion efficiency Region with low conversion efficiency (1) (2) (3)Fig.4 Frequency during burst operation HO LO VS Aux Vi Fig.5 Schematic circuit diagram of current resonance R1 VW Aux Delay circuit Tolpdly = 76.8 ms Delay circuit Tolpoff = 550 ms SQ R Stop switching Volpvw Fig.6 Circuit confi guration of high-precision overload protection function
248 FUJI ELECTRIC REVIEW vol.59 no.4 2013 degree of fl exibility in power supply design. With the FA6A00N Series, adjustment of Tocp is shared by the MODE terminal for state setting, which has led to the realization of the over-current protection function with a variable delay time without increasing the number of terminals. Figure 9 shows a measured waveform. When a resonant current rapidly increases, an over-current state is detected on the IS terminal. The MODE terminal voltage is clamped to 0.5 V after state setting and, when an overload state is detected, oscillates between 0.6 and 0.8 V. When the number of oscillations reaches 36, switching stops and provides over-current protection. The duration of one oscilla- tion can be adjusted by the capacitor connected to the MODE terminal. 4. Effect on Application to Power Circuit
4.1 Standby power reduction effect
Figure 10 shows a sample application circuit and Tables 4 and 5 the speci fi cation of the sample appli- cation circuit and major semiconductor components in the circuit. Figure 11 shows the measured standby power with a 35 mW load. The FA6A00N Series can reduce the standby power by approximately 20% from FA5760N, which allows elimination of the standby converter even if requirements for standby power are severe.
4.2 Number of circuit components reduction effect
Figure 12 shows the confi guration of a general LLC current resonant power supply. A general LLC cur- rent resonant power supply is composed of a fi lter for EMI (electromagnetic interference) noise elimination, PFC converter for power factor correction, standby con- verter and LLC converter. Use of the FA6A00N Series allows signi fi cant reduction in the number of compo- nents, making it possible to build a low-cost LLC cur- rent resonant power supply (see Table 6). protection level is highly dependent on the input volt- age when the input voltage range is wide, and this has necessitated the addition of a dedicated overload pro- tection circuit. With the FA6A00N Series, variation of the overload protection level is small even if the input voltage varies, allowing for a high-accuracy overload protection function without a dedicated overload pro- tection circuit. As a result, the number of power sup- ply system components can be reduced, allowing for a cost reduction of a power supply system.
3.3 Over-current protection function with variable delay
When a load short circuit occurs and an over- current state has continued for the speci fi ed time Tocp, switching stops. This is called the over-current protec- tion function. The power device has a possibility of being damaged if the Tocp setting is too long. If the T ocp setting is too short, it causes an over-current state at start-up, and this may be detected as a load short circuit state and might hinder the start-up. The opti- mum T ocp depends on a power supply and capability to adjust Tocp with an external component offers a higher Output voltage Vo Peak value of VW voltage: 2.8 VPeak value of VW voltage: 2.8 V Reference value of VW voltage: 0 VReference value of VW voltage: 0 V VW voltage Fig.7 Operation waveform during overload protection Input voltage (V) 100 150 200 250 300 FA6A00N Series FA5760N Overload protection level (W) 300 200 100 400 Fig.8 Input voltage and overload protection operating power Resonant current IS voltage MODE voltage VS voltage Fig.9 Waveform during over-current protection operation
2492nd Generation LLC Current Resonant Control IC, “FA6A00N Series” issue: Power Semiconductors Contributing in Energy Management Table 4 Specifi cations of sample application circuit Item Characteristic, etc. Input voltage 85 to 264 V AC Output voltage/current 24 V/3 A, 12 V/2 A, 5 V/1 A Output power 100 W (max.) Table 5 Major semiconductor components in sample applica- tion circuit Component Model Control IC FA6A00N Series Bridge MOSFET FMV23N50E (500 V/23 A/0.245 Ω) Diode (24 V) YG865C10R (100 V/20 A) Diode (12 V) YG862C06R (60 V/10 A)
5 V AC/DC converter FA7764AN
Input voltage (V) 100 150 200 250 300 Standby power (mW) 150 100 200 Fig.11 Standby power with 35 mW load Input 85 to
264 V AC
+FA7764 1234 87 65 PC1 PC2 On-Off signal input GND Output 3 5V/1A GND Output 2
12 V/2 A
24 V/3 A
(100 V/20 A) YG862C06R (60 V/10 A) FMV23N50E ʢ500 V/23 A/ 0245 ʣ /0.245 ʣ FMV23N50E (500 V/23 A/ 0.245 ) /0.245 VBVH STB CS VCC MODE FB VW GND IS LO VS HO BO/PGS FA6A00N Series PC1 Fig.10 Sample application circuit + Output Filter PFC converter Standby converter LLC converter VS +PFC control IC LLC control IC OLP circuit DC-DC circuit Output PWM (pulse width modulation) control IC Vac Vi VCC Fig.12 Confi guration of general LLC current resonant power supply
250 FUJI ELECTRIC REVIEW vol.59 no.4 2013 tion of current resonant control with features including the high-precision overload protection function. We intend to continue working on establishing new technologies that realize even higher ef fi ciency and further noise reduction, and developing power supply control ICs that contribute to the miniaturization and profi le lowering of power supply. 5. Postscript This paper has described the 2nd-generation LLC current resonant control IC “FA6A00N Series.” This IC, which inherits the characteristics of the 1st-gener- ation product “FA5760N,” has achieved further evolu- Table 6 Comparison on number (approximate number) of components Filter PFC converter Standby converter LLC converter Total number of componentsMain DC-DC High-precision OLP FA5760N 10 30 40 60 Not required 10 150 FA6A00N Series
75 W or more 10 30 Not required 60 20 Not required 120
less than 75 W 10 Not required Not required 60 20 Not required 90
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