ST AN4027 APPLICATION NOTE

AN4027

Application note

12 V - 150 W resonant converter with synchronous rectification using the L6563H, L6699 and SRK2000

By Claudio Spini

Introduction

This application note describes the EVL6699-150W-SR demonstration board features, a 12 V - 150 W converter tailored to a typical specification of an all-in-one (AIO) computer power supply or a high power adapter.

The architecture is based on a two-stage approach: a front-end PFC pre-regulator based on the L6563H TM PFC controller and a downstream LLC resonant half bridge converter using the new L6699 resonant controller. The L6699 integrates some very innovative functions such as self-adjusting adaptive deadtime, anti-capacitive mode protection and proprietary “safe-start” procedure preventing hard switching at startup.

Thanks to the chipset used, the main features of this power supply are very high efficiency, compliant with ENERGY STAR® eligibility criteria for adapters (ENERGY STAR® rev. 2.0 for external power supplies) and with the latest ENERGY STAR® qualification criteria for computers (ENERGY STAR® ver. 6.0 for computers). The power supply also has very good efficiency at light load too, and compliance to the new EuP Lot 6 Tier 2 requirements. No load input power consumption is very low as well, within the international regulation limits.

Figure 1. EVL6699-150W-SR: 150 W SMPS demonstration board

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Contents	AN4027

Contents

1	Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . .		. 5
	1.1	Standby power saving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	6
	1.2	Startup sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	8
	1.3	L6563H brownout protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	8
	1.4	L6563H fast voltage feed-forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	8
	1.5	L6699 overload and short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . .	9
	1.6	L6699 anti-capacitive protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
	1.7	Output voltage feedback loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	10
	1.8	Open loop protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	10

2	Efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		12
	2.1	ENERGY STAR® for external power supplies ver. 2.0 compliance verification
		. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	13
	2.2	ENERGY STAR® for computers ver. 6.0 compliance verification . . . . . . .	13
	2.3	Light load operation efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	13

Measurement procedure: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3	Harmonic content measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		15
4	Functional check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		16
	4.1	Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	19
	4.2	Burst mode operation at light load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	20
	4.3	Overcurrent and short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . .	21
	4.4	Anti-capacitive mode protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	23
5	Thermal map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		24
6	Conducted emission pre-compliance test . . . . . . . . . . . . . . . . . . . . . .		26
7	Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		27
8	PFC coil specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		32
	8.1	General description and characteristics . . . . . . . . . . . . . . . . . . . . . . . . . .	32

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8.2 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 8.3 Electrical diagram and winding characteristics . . . . . . . . . . . . . . . . . . . . . 33 8.4 Mechanical aspect and pin numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 8.5 Manufacturer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

9	Transformer specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		34
	9.1	General description and characteristics . . . . . . . . . . . . . . . . . . . . . . . . . .	34
	9.2	Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	35
	9.3	Electrical diagram and winding characteristics . . . . . . . . . . . . . . . . . . . . .	35
	9.4	Mechanical aspect and pin numbering . . . . . . . . . . . . . . . . . . . . . . . . . . .	36
	9.5	Manufacturer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	36
10	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		37

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List of tables	AN4027

List of tables

Table 1. Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Table 2. Efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Table 3. ENERGY STAR® for external power supplies ver. 2.0 compliance verification . . . . . . . . . 14 Table 4. ENERGY STAR® for computers ver. 6.0 compliance verification. . . . . . . . . . . . . . . . . . . . 14 Table 5. Light load efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Table 6. Thermal maps reference points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Table 7. EVL6699-150W-SR demonstration board: motherboard bill of material. . . . . . . . . . . . . . . 27 Table 8. EVL6699-150W-SR demonstration board: daughterboard bill of material . . . . . . . . . . . . . 31 Table 9. PFC coil winding data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Table 10. Transformer winding data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Table 11. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

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AN4027	List of figures

List of figures

Figure 1. EVL6699-150W-SR: 150 W SMPS demonstration board. . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Figure 2. Burst-mode circuit block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 3. Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Figure 4. Graph of efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Figure 5. Light load efficiency diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 6. Compliance to EN61000-3-2 at 230 Vac - 50 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . 16 Figure 7. Compliance to JEITA-MITI at 100 Vac - 50 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Figure 8. Mains voltage and current waveforms at 230 V - 50 Hz - full load . . . . . . . . . . . . . . . . . . . 17

Figure 9. Mains voltage and current waveforms at 100 V - 50 Hz - full load . . . . . . . . . . . . . . . . . . . 17

Figure 10. Resonant stage waveforms at 115 Vac - 60 Hz - full load. . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 11. SRK2000 key signals at 115 Vac - 60 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 12. HB transition at full load - rising edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 13. HB transition at full load - falling edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 14. HB transition at 0.25 A - rising edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 15. HB transition at 0.25 A - falling edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 16. L6699 pin signals-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 17. L6699 pin signals-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 18. Startup at 90 Vac - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 19. Startup at 265 Vac - no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 20. Startup at 115 Vac - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Figure 21. Startup at full load - detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 22. Pout = 250 mW operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Figure 23. Pout = 250 mW operation - detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 24. Transition full load to no load at 115 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 25. Transition no load to full load at 115 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 26. Short-circuit at full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 27. Short-circuit at full load – detail. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 28. Short-circuit - hiccup mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 29. Thermal map at 115 Vac - 60 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 30. Thermal map at 230 Vac - 50 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 31. CE average measurement at 115 Vac - 60 Hz and full load. . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 32. CE average measurement at 230 Vac - 50 Hz and full load. . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 33. PFC coil electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Figure 34. PFC coil mechanical aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Figure 35. Transformer electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Figure 36. Transformer overall drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

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Main characteristics and circuit description	AN4027

1 Main characteristics and circuit description

The SMPS main features are listed below:

Table 1.	Main characteristics and circuit description
	Parameter	Value
Input mains range		90 - 264 Vac - frequency 45 to 65 Hz
Output voltage		12 V at 12.5 A continuous operation
Mains harmonics		Meets EN61000-3-2 Class-D and JEITA-MITI Class-D
No load mains consumption		< 0.17 W at 230 Vac, according to ENERGY STAR® 2.0
		for external power supplies
Avg. efficiency		> 91% at 115 V , according to ENERGY STAR® 2.0
		ac
		for external power supplies
Light load efficiency		According to EuP Lot 6 Tier 2 requirements
EMI		Within EN55022 Class-B limits
Safety		Meets EN60950
Dimensions		65 x 154 mm, 28 mm component maximum height
PCB		Double side, 70 µm, FR-4, mixed PTH/SMT

The circuit is made up of two stages: a front-end PFC using the L6563H, an LLC resonant converter based on the L6699, and the SRK2000, controlling the SR MOSFETs on the secondary side. The SR driver and the rectifier MOSFETs are mounted on a daughterboard.

The L6563H is a current mode PFC controller operating in transition mode and implements a high-voltage startup to power on the converter.

The L6699 integrates all the functions necessary to properly control the resonant converter with a 50 % fixed duty cycle and working with variable frequency.

The output rectification is managed by the SRK2000, an SR driver dedicated to LLC resonant topology.

The PFC stage works as pre-regulator 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.

The L6699 LINE pin (pin 7) is dedicated to this function. It is used to prevent the resonant converter from working with too low input voltage that can cause incorrect Capacitive mode operation. If the bulk voltage (PFC output) is below 380 V, the resonant startup is not allowed. The L6699 LINE pin internal comparator has a current hysteresis allowing the turnon and turn-off voltage to be independently set. The turn-off threshold has been set to 300 V to let the resonant stage operate in the case of mains sag and consequent PFC output dip.

The transformer uses the integrated magnetic approach, incorporating the resonant series inductance. Therefore, no external, additional coil is needed for the resonance. The transformer configuration chosen for the secondary winding is centre tap.

On the secondary side, the SRK2000 core function is to switch on each synchronous rectifier MOSFET whenever the corresponding transformer half-winding starts conducting

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(i.e. when the MOSFET body diode starts conducting) and then to switch it off when the flowing current approaches zero. For this purpose, the IC is provided with two pins (DVS1 and DVS2) sensing the MOSFETs drain voltage level.

The SRK2000 automatically detects light load operation and enters sleep mode, disabling MOSFET driving and decreasing its own consumption. This function allows great power saving at light load with respect to benchmark SR solutions.

In order to decrease the output capacitors size, aluminium solid capacitors with very low ESR were preferred to standard electrolytic ones. Therefore, high frequency output voltage ripple is limited and an output LC filter is not required. This choice allows the saving of output inductor power dissipation which can be significant in the case of high output current applications such as this.

1.1Standby power saving

The board has a burst mode function implemented that allows power saving during light load operation.

The L6699 STBY pin (pin 5) senses the optocoupler’s collector voltage (U3), 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 30 mV, the controller restarts the switching. The burst mode operation load threshold can be programmed by properly choosing the resistor connecting the optocoupler to pin RFMIN (R34). Basically, R34 sets the switching frequency at which the controller enters burst mode. Since the power at which the converter enters burst mode operation heavily influences converter efficiency at light load, it must be properly set. However, despite this threshold being well set, if its tolerance is too wide, the light load efficiency of mass production converters has a considerable spread.

The main factors affecting the burst mode threshold tolerance are the control circuitry tolerances and, even more influential, the tolerances of the resonant inductance and resonant capacitor. Slight changes of resonance frequency can affect the switching frequency and, consequently, notably change the burst mode threshold. Typical production spread of these parameters, which fits the requirements of many applications, are no longer acceptable if very low power consumption in standby must be guaranteed.

As reducing production tolerance of the resonant components causes a rise in cost, a new cost-effective solution is necessary.

The key point of the proposed solution is to directly sense the output load to set the burst mode threshold. In this way the resonant elements parameters no longer affect this threshold. The implemented circuit block diagram is shown in Figure 2.

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Main characteristics and circuit description	AN4027

Figure 2. Burst-mode circuit block diagram

				TO POWER TRANSFORMER
									2#3	TO LOAD
	TO &" OPTOCOUPLER
, !		2&-).		2LIM	43-			43#
	6	2&"							60
						##	/54
								% !
						6?2%&			6-
		34"9		##?/54			2(
					#OMP	6
3TANDBY
	#OMP					##
							2,
	6	2"-	2"-
					2(TS
										!-6

The output current is sensed by a resistor (RCS); the voltage drop across this resistor is amplified by the TSC101, a dedicated high-side current sense amplifier; its output is compared to a set reference by the TSM1014; if the output load is high, the signal fed into the CCpin is above the reference voltage, CC_OUT stays down and the optocoupler transistor pulls up the L6699 STBY pin to the RFMIN voltage (2 V), setting continuous switching operation (no burst mode); if the load decreases, the voltage on CCfalls below the set threshold, CC_OUT goes high opening the connection between RFMIN and STBY and allowing burst mode operation by the L6699. RCS is dimensioned considering two constraints. The first is the maximum power dissipation allowed, based on the efficiency target. The second limitation is imposed by the need to feed a reasonable voltage signal into the TSM1014A inverting input. In fact, signals which are too small would affect system accuracy.

On this board, the maximum acceptable power dissipation has been set to Ploss,MAX = 500 mW. RCS maximum value is calculated as follows:

Equation 1

RCS,MAX = PIlo2 ss,MAX = 3.2mΩ out,MAX

The burst mode threshold is set at 5 W corresponding to IBM = 417 mA output current at

12 V. Choosing VCC+min = 50 mV as minimum reference of the TSM1014A, which permits a good signal to noise ratio, the RCS minimum value is calculated as follows:

Equation 2

RCS,min =	VCC+min		= 1.2mΩ
	100	• I
		BM

The actual value of the mounted resistor is 2 mΩ, corresponding to Ploss = 312 mW power losses at full load. The actual resistor value at the burst mode threshold current provides an output voltage by the TSC101 of 83 mV. The reference voltage of TSM1014 Vcc+ must be

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set at this level. The resistor divider setting the TSM1014 threshold RH and RL should be in the range of kΩ to minimize dissipation. Selecting RL = 22 KΩ, the right RH value is obtained as follows:

Equation 3

RH = RL (1.25V − VBM ) = 309kΩ

VBM

The value of the mounted resistor is 330 kΩ.

RHts sets a small debouncing hysteresis and is in the range of mega ohms. Rlim is in the range of tens of kΩ and limits the current flowing through the optocoupler's diode. Both L6699 and L6563H implement their own burst mode function but, in order to improve the power supply overall efficiency, at light load the L6699 drives the L6563H via the PFC_STOP pin and enables the PFC burst mode: as soon as the L6699 stops switching due to load drops, its PFC_STOP pin pulls down the L6563H PFC_OK pin, disabling PFC switching. Thanks to this simple circuit, the PFC is forced into idle state when the resonant stage is not switching and rapidly wakes up when the downstream converter restarts switching.

1.2Startup sequence

The PFC acts as master and the resonant stage can operate only if the PFC output is delivering the rated output voltage. Therefore, the PFC starts first and then the LLC converter turns on. At the beginning, the L6563H is supplied by the integrated high-voltage startup circuit; as soon as the PFC starts switching, a charge pump circuit connected to the PFC inductor supplies both PFC and resonant controllers, therefore, the HV internal current source is disabled. 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. As the L6563H integrated HV startup circuit is turned off, it greatly contributes to power consumption reduction when the power supply operates at light load.

1.3L6563H brownout protection

Brownout protection prevents the circuit from working with abnormal mains levels. It is easily achieved using the RUN pin (pin 12) of the L6563H: this pin is connected through a resistor divider to the VFF pin (pin 5), which provides the information of the mains voltage peak value. 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.

1.4L6563H 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 a peak-holding circuit. This signal is necessary to derive information from the RMS input voltage to compensate the loop gain that 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, therefore causing distortion of

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Main characteristics and circuit description	AN4027

the current reference (resulting in higher THD and lower 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 pre-regulator's output voltage in response to large line voltage changes.

To overcome this issue, the L6563H implements the fast voltage feed-forward function. As soon as the voltage on the VFF pin decreases by a set threshold (40 mV typically), a mains dip is assumed and an internal switch rapidly discharges the VFF capacitor via a 10 kΩ resistor. Thanks to this feature, it is possible to set an RC circuit with a long time constant, assuring a low THD, keeping a fast response to mains dip.

1.5L6699 overload and short-circuit protection

The current into the primary winding is sensed by the lossless circuit R41, C27, R78, R79, and C25 and it is fed into the ISEN pin (pin 6). In the case of overload, the voltage on the pin surpasses an internal threshold (0.8 V) that triggers a protection sequence. An internal switch is turned on for 5 µs and discharges the soft-start capacitor C18. This quickly increases the oscillator frequency and thereby limits energy transfer. Under output shortcircuit conditions, this operation results in a peak primary current that periodically oscillates below the maximum value allowed by the sense resistor R78.

The converter runs under this condition for a time set by the capacitor (C45) on pin DELAY (pin 2). During this condition, C45 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 because of the external resistor. The IC is soft-restarted as the voltage drops below 0.3 V. In this way, under shortcircuit conditions, the converter works intermittently with very low input average power.

This procedure allows the converter to handle an overload condition for a time lasting less than a set value, avoiding IC shutdown in the case of short overload or peak power transients. On the other hand, in the case of dead short, a second comparator referenced to

1.5 V immediately disables switching and activates a restart procedure.

1.6L6699 anti-capacitive protection

The LLC resonant half bridge converter must operate with the resonant tank current lagging behind the square-wave voltage applied by the half bridge leg. This is a necessary condition in order to obtain correct soft switching by the half bridge MOSFETs. If the phase relationship reverses, i.e. the resonant tank current leads the applied voltage, like in circuits having a capacitive reactance, soft switching is lost. This condition is called capacitive mode and must be avoided because of significant drawbacks coming from hard switching (refer to the L6699 datasheet).

Resonant converters work in capacitive mode when their switching frequency falls below a critical value that depends on the loading conditions and the input-to-output voltage ratio. They are especially prone to run in capacitive mode when the input voltage is lower than the minimum specified and/or the output is overloaded or short-circuited. Designing a converter so that it never works in capacitive mode, even under abnormal operating conditions, is certainly possible but this may pose unacceptable design constraints in some cases.

To prevent the severe drawbacks of capacitive mode operation, while enabling a design that needs to ensure Inductive mode operation only in the specified operating range, neglecting

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Doc ID 022604 Rev 1

AN4027	Main characteristics and circuit description

abnormal operating conditions, the L6699 provides the capacitive mode detection function. The IC monitors the phase relationship between the tank current circuit sensed on the ISEN pin and the voltage applied to the tank circuit by the half bridge, checking that the former lags behind the latter (Inductive mode operation). If the phase shift approaches zero, which is indicative of impending capacitive mode operation, the monitoring circuit activates the overload procedure described above so that the resulting frequency rise keeps the converter away from that dangerous condition. Also in this case, the DELAY pin is activated, so that the OLP function, if used, is eventually tripped after a time TSH causing intermittent operation and reducing thermal stress.

If the phase relationship reverses abruptly (which may happen in the case of dead short at the converter's output), the L6699 is stopped immediately, the soft-start capacitor C18 is totally discharged and a new soft-start cycle is initiated after 50 µs idle time. During this idle period the PFC_STOP pin is pulled low to stop the PFC stage as well.

1.7Output voltage feedback loop

The feedback loop is implemented by means of a typical circuit using the dedicated operational amplifier of the TSM1014A modulating the current in the optocoupler diode. The second operational amplifier embedded in the TSM1014A, usually dedicated to constant current regulation, is here utilized for burst mode as previously described.

On the primary side, R34 and D17 connect the RFMIN pin (pin 4) to the optocoupler's photo transistor closing the feedback loop. R31, which connects the same pin to ground, sets the minimum switching frequency. The RC series R44 and C18 sets both soft-start maximum frequency and duration.

1.8Open loop protection

Both circuit stages, PFC and resonant, 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 or disconnection. If a fault condition is detected, the internal circuitry latches the L6563H operations and, by means of the PWM_LATCH pin (pin 8), it latches the L6699 as well via the DIS pin (pin 8). The converter is kept latched by the L6563H internal HV startup circuit that supplies the IC by charging the Vcc capacitor periodically. To resume converter operation, mains restart is necessary. The LLC open loop protection is realized by monitoring the output voltage through sensing the Vcc voltage. If Vcc voltage overrides the D12 breakdown voltage, Q9 pulls down the L6563H INV pin latching the converter. Even in this case, to resume converter operation, mains restart is necessary.

Doc ID 022604 Rev 1

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12/38

1 Rev 022604 ID Doc

D3

1N4005

F1

L1

D1

L2

2

1

R6

J1

FUSE T4A

C20

2019.0002

GBU8J

1975.0004

NTC 2R5-S237

MKDS 1,5/ 3-5,08

2

4

9

5

2

1

2N2-Y1

1

C2

1

2

~

+

11

3

D4

2N2-Y1

C4

2

C1

STTH5L06

3

470N-X2

470N-X2

C5

C9

C21

90-264Vac

C3

4

3

3

~

_

1

100uF - 450V

2N2-Y1

2N2-Y1

470N - 520V

R7

R17

R5

C7

D5

2M2

2M2

75R

100N

LL4148

2	1
1

			D2		C8
			LL4148	2	10uF-50V			R3	R11
R1
								2M2	2M2
6M8
			Q8				D21
			BC847C				LL4148
			2		3		1	2
R2		2		1				R8	R12
5M6			D7			R69
								2M2	2M2
					D20
		1	STPS140Z			24K
				2	BZV55-B15
		R10							R13
C14	R9								9K1
68N	160K	56K

R14

100K

			C11
			2N2
		R37
		220K
R75		D13
		N.M.
0R0	1	C12
	2	1uF	R15
3			56K

BC847C	1
Q9	R76	1N0
2
	33K	C52

	2	R26
	D12
		1M0
	BZV55-C43
	1

1K0

R77

0R0

R54

				U1	C15	C39	R19
				L6563H	47uF-50V	100N
							56K
C13	R18
		1		VCC16
680N 82K			INV						D14	R45
									LL4148 3R3
		2	COMP	GD 15					1	2
		3	MULT	GND14					R21
		4	CS	ZCD13					22R
		5	VFF	RUN12		C16		R55	R20	C33
									33R
	C22	6	TBO PWM-STOP11			2N2		2K7		1N5
	220pF	7		NC 10					R52
			PFC-OK			3		2	1K5
C10		8	PWM-LATCHHVS9
									D6
1N0	C31					Q2
							1		LL4148
	N.M.					BC857		R53
				R27				2K2
				470R

Q1

2 STF21NM65M5

1

R46

3

100K

R22 R23

0R22 0R22

HS1

HEAT-SINK

R67

R29 N.M.

1K0

1

C46

N.M.

R60

10K

Q7
N.M.
2		C45
	C18	220NF	R24
	4u7F		1M0
3
						D16
		R4	R16		1	N.M.
	R44	N.M.	2K7
R33			C6		2
	6K2
N.M.			330NC17
			330PF
	R31
	20K	R32	R36 C44
		47R	1M8	1.5NF
	R34	C23
		10N
	8K2		C43			R30
			4N7			10R

	U2		C19
	L6699D
			100N
1	CSS		VBOOT16
2	DELAY		HVG15
3	CF		OUT14
4	RFMIN		NC 13
5	STBY		VCC12
6	ISEN		LVG 11
7	LINE		GND10	C40	C26
8	DIS	PFC-STOP9		100N 10uF-50V

R28 R35

33K 180K

D18			Q3
			STF8NM50N
LL4148
				2
1	2
			1
R25		R58		3
56R		100K
	D19
	LL4148			2
	1	2
			1
	R38		R59	3	Q4
	56R		100K		STF8NM50N
JPX1				C27
			R79
				220PF-630V R41
			270R		100R
	C25	R39		R78
	1.5NF N.M.			33R

D9 R40

STPS2H100A 0R68

1 2

C24

220uF-50V

CONNECTION MADE BY REWORK

D17

LL4148

2

1

97v13AM11

	RX1		R504				R503
							10R
	0R0		150K
JP501			C502
1	C501	R505
			100NF				C503	D501
2	4nF7	33k							Q501
3				U501			1uF	BAS316
4									STL140N4LLF5
5				SRK2000
6			1 SGND VCC8
7								R501
8								10R
9	R506		2	EN	GD1	7
10	330R
11
12			3	DVS1 PGND6				R502
13	R508	C504
		N.M.	4 DVS2		GD2 5			10R
	N.M.
	D503								Q502
	N.M.								STL140N4LLF5
			C505					D502
	R507R509							BAS316
			N.M.
	330RN.M.
	D505
	N.M.
EVLSRK2000-L-40

T1

1860.0069

2
4	8
	9

C28

10

22NF 11 12

6	13
	14

7

1

2

3

4

5

6

7

8

9

10

11

12 13

							U6
						1	Out Vcc 5
						2 GND
						3	Vp Vm 4
							TSC101
							R57
							R002
				1
				D15			R66
C29				N.M.		R65	N.M.
						N.M.
470uF-16V C30	C49	C50	C37	R562
470uF-16V 470uF-16V 470uF-16V 470uF-16V						3	Q6
						1
				N.M.	3		N.M.
				1		Q5
						N.M.2

R62	2
N.M.

R42

R43

1K0

51R

C36

R74

1uF - 50V

C48

N.M.

R73

1N0

U5

R68

22R

R71

R72

TSM1014AIST

5K6

330K

1 V_REF VCC8

C51

1K0

C41

100N

2 CCCC_OUT7

N.M.

4

1

C32

R47

470N

3

6

R49

CC+

GND

N.M.

U3

91K

C47

R70

4 CVCV_OUT5

3

2

22K

SFH617A-2

1N0

C34

R48

R50

R51

100N

47K

12K

91K

R64

10Meg

C35

Rev 1.3

N.M.

U4

SFH617A-2

4

1

3

2

R63

0R0 C42

100N

12V-12.5A J3

FASTON

C38

R61 100N N.M.

J2

FASTON

diagram Electrical .3 Figure	circuit and characteristics Main
	description

AN4027