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 external power supplies) and with the latest ENERGY STAR computers (ENERGY STAR 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

eligibility criteria for adapters (ENERGY STAR® rev. 2.0 for

ver. 6.0 for computers). The power supply also has very good

qualification criteria for

July 2012 Doc ID 022604 Rev 1 1/38

www.st.com

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

2.3 Light load operation efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

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

for computers ver. 6.0 compliance verification . . . . . . . 13

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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AN4027 Contents

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

Doc ID 022604 Rev 1 3/38

List of tables AN4027

List of tables

Table 1. Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Table 2. Efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Table 3. ENERGY STAR Table 4. ENERGY STAR

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

for external power supplies ver. 2.0 compliance verification . . . . . . . . . 14

for computers ver. 6.0 compliance verification. . . . . . . . . . . . . . . . . . . . 14

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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 V Figure 7. Compliance to JEITA-MITI at 100 V

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 V Figure 11. SRK2000 key signals at 115 V

- 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 V Figure 19. Startup at 265 V Figure 20. Startup at 115 V

- full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

- no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

- 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 V Figure 25. Transition no load to full load at 115 V

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 V Figure 30. Thermal map at 230 V

- 60 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

- 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

- 50 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . 16

- 50 Hz, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

- 60 Hz - full load. . . . . . . . . . . . . . . . . . . . . . . . . . 17

- 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Doc ID 022604 Rev 1 5/38

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 V

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

Avg. efficiency

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

< 0.17 W at 230 V

for external power supplies

> 91% at 115

for external power supplies

- frequency 45 to 65 Hz

, according to ENERGY STAR® 2.0

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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AN4027 Main characteristics and circuit description

(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.

1.1 Standby 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

Doc ID 022604 Rev 1 7/38

Main characteristics and circuit description AN4027

Figure 2. Burst-mode circuit block diagram

TOP

OWERTRANSFORMER

TO&"OPTOCOUPLER

TOLOAD

,! 43-

3TANDBY

#OMP

6

2&-).

6

34"9





2"-2

LIM

##?/54

#OMP

(TS





The output current is sensed by a resistor (R

## /54

6?2%&

6

##

); the voltage drop across this resistor is

43#



%!

(





!-6

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 CC- pin 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 CC- falls below the set threshold, CC_OUT goes high opening the connection between RFMIN and STBY and allowing burst mode operation by the L6699. R

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 P mW. R

maximum value is calculated as follows:

loss,MAX

= 500

Equation 1

MAXCS,

MAXlo ss,

MA Xout,

The burst mode threshold is set at 5 W corresponding to I 12 V. Choosing V good signal to noise ratio, the R

= 50 mV as minimum reference of the TSM1014A, which permits a

CC+min

minimum value is calculated as follows:

Equation 2

minCS,

The actual value of the mounted resistor is 2 mΩ, corresponding to P 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 V

8/38 Doc ID 022604 Rev 1

•

3.2mΩ=

= 417 mA output current at

min+CC

I 100

1.2mΩ=

= 312 mW power

loss

must be

cc+

AN4027 Main characteristics and circuit description

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 R as follows:

Equation 3

= 22 KΩ, the right RH value is obtained

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.

1.2 Startup 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.

()

V1.25VR

−

BML

309kΩ

1.3 L6563H 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 V inhibited.

1.4 L6563H 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

Doc ID 022604 Rev 1 9/38

(typ.), circuit operations are

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.

1.5 L6699 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.

1.6 L6699 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

10/38 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.

1.7 Output 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.

1.8 Open 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 V operation, mains restart is necessary. The LLC open loop protection is realized by monitoring the output voltage through sensing the V 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.

capacitor periodically. To resume converter

voltage. If Vcc voltage overrides the

Doc ID 022604 Rev 1 11/38

Main characteristics and circuit description AN4027

Figure 3. Electrical diagram

C16

RUN

R37

FASTON

R66

N.M.

R65

N.M.

D15

C29

R23

0R22

R23

R22

0R22

R22

C33

1N5

33R

R55

2K7

R55

2K7

2N2

PWM-STOP

C22

220K

C38

100N

R61

N.M.

R61

N.M.

3 2

2 1

N.M.

R56

C37

470uF-16V

C50

470uF-16V

C49

C30

470uF-16V

34567891011

C28

22NF

HS1

R52

1K5

HVS

220pF

C10

D13

N.M.

R75

0R0

R75

0R0

N.M.

1N0

FASTON

R68

STF8NM50N

100K

HVG

2K7

N.M.

R44

R33

5K6

C51

100N

R73

22R

R74

N.M.

VCC

GND

CV_OUT

CC_OUT

V_REF

CC+3CC-

TSM1014AIST

C48

1N0

R70

R72

330K

R71

1K0

C32

470N

R49

91K

R49

R43

51R

R43

51R

C36

1uF - 50V

C36

1uF - 50V

R42

1K0

R42

1K0

56R

VCC

OUT

C17

330PF

330N

6K2

R31

N.M.

R54

0R0

R77

1K0

91K

R47

N.M.

R47

N.M.

1 2

4 3

C41

N.M.

R41

100R

R78

33R

C27

220PF-630V

R79

270R

N.M.

R39

C25

1.5NF

JPX1JPX1

C26

10uF-50V

C40

100N

LVG

GND

PFC-STOP

DIS

R30

C44

1.5NF

C44

1.5NF C43

R36

1M8

R36

1M8

10N

C23

R32

47R

R32

47R

R34

8K2

20K

R60

10K

CV-

22K

C47

SFH617A-2

10R

4N7

1N0

R51

R50

R48

47K

R48

47K

C34

100N

C34

100N

R40

0R68

1 2

STPS2H100A

Rev 1.3

R64

10Meg

91K

12K

C35

N.M.

C35

N.M.

C24

220uF-50V

CONNECTION MADE BY REWORK

SFH617A-2

D17

LL4148

AM11397v1

R62

N.M.

R62

12138

100K

D19

56R

R24

1M0

C45

220NF

4u7F

C18

R67

N.M.

R29

1K0

R29

1K0

BZV55-C43

213

R59

R38

LL4148

1 2

C19

100N

VBOOT

CSS1DELAY2CF3RFMIN4STBY5ISEN6LINE

L6699D

D16

N.M.

R16

N.M.

C46

213

STF8NM50N

R58

D18

LL4148

R25

1 2

HEAT-SINK

LL4148

R53

2K2

BC857

R27

470R

N.M.

C31

N.M.

C31

R15

56K

R15

56K

R26

1M0

R26

1N0

C52

C12

1uF

D12

R76

33K

BC847C

C42

100N

0R0

R63

STL140N4LLF5

R501

10R

VCC

SRK2000

SGND1EN2DVS13DVS2

R506

2M2

R11

2M2

10uF-50V

LL4148

6M8

Q502

STL140N4LLF5

R502

D502

BAS316

10R

GD2

GD1

PGND

N.M.

C505

C504

N.M.

R508

N.M.

R509

N.M.

R507

330R

D21

330R

D505

N.M.

D503

N.M.

R12

2M2

LL4148

1 2

R69

BC847C

5M6

24K

D20

BZV55-B15

STPS140Z

EVLSRK2000-L-40

R13

9K1

56K

R10

160K

C14

68N

R19

C39

C15

47uF-50V

L6563H

Q501

D501

BAS316

R503

10R

C503

1uF

U501

C502

100NF

R504

150K

R505

33k

C501

4nF7

RX1

0R0

123456789

JP501JP501

2N2-Y1

C20

2N2-Y1

C21

100uF - 450V

R17

2M2

NTC 2R5-S237

STTH5L06

1N4005

1975.0004

2019.0002

FUSE T4A

GBU8J

MKDS 1,5/ 3-5,08

11 3

124

2N2-Y1

470N-X2

3 1

2N2-Y1C32N2-Y1

90-264Vac

LL4148

1 2

100N

75R

470N - 520V

12V-12.5A

Vcc

R57

R002

TSC101

Out

GND2Vp

1860.0069

R35

180K

R28

33K

STF21NM65M5

213

R46

100K

R46

R45

3R3

R21

22R

R20

D14

LL4148

1 2

56K

100N

ZCD

VCC

GND

INV1COMP2MULT3CS4VFF5TBO6PFC-OK7PWM-LATCH

82K

R18

680N

C13

2N2

C11

R14

100K

12/38 Doc ID 022604 Rev 1

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