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March 2010

FSQ0765RS

Green-Mode Fairchild Power Switch (FPS™) for

Quasi-Resonant Operation - Low EMI and High Efficiency

Features

Description

! Optimized for Quasi-Resonant Converter (QRC)

! Low EMI through Variable Frequency Control and AVS

A Quasi-Resonant Converter (QRC) generally shows

lower EMI and higher power conversion efficiency than a

(Alternating Valley Switching)

conventional hard-switched converter with a fixed

switching frequency. The FSQ-series is an integrated

Pulse-Width Modulation (PWM) controller and

SenseFET specifically designed for quasi-resonant

operation and Alternating Valley Switching (AVS). The

PWM controller includes an integrated fixed-frequency

oscillator, Under-Voltage Lockout (UVLO), Leading-

Edge Blanking (LEB), optimized gate driver, internal soft-

start, temperature-compensated precise current sources

for a loop compensation, and self-protection circuitry.

Compared with a discrete MOSFET and PWM controller

solution, the FSQ-series can reduce total cost,

component count, size, and weight; while simultaneously

increasing efficiency, productivity, and system reliability.

This device provides a basic platform for cost-effective

designs of quasi-resonant switching flyback converters.

! High Efficiency through Minimum Voltage Switching

! Narrow Frequency Variation Range over Wide Load

and Input Voltage Variation

! Advanced Burst-Mode Operation for Low Standby

Power Consumption

! Simple Scheme for Sync-Voltage Detection

! Pulse-by-Pulse Current Limit

! Various Protection functions: Overload Protection

(OLP), Over-Voltage Protection (OVP), Abnormal

Over-Current Protection (AOCP), Internal Thermal

Shutdown (TSD) with Hysteresis, Output Short

Protection (OSP)

! Under-Voltage Lockout (UVLO) with Hysteresis

! Internal Startup Circuit

! Internal High-Voltage Sense FET (650V)

! Built-in Soft-Start (17.5ms)

Applications

! Power Supply for LCD TV and Monitor, VCR, SVR,

STB, and DVD & DVD Recorder

! Adapter

Related Resources

Visit: http://www.fairchildsemi.com/apnotes/ for:

! AN-4134: Design Guidelines for Off-line Forward

Converters Using Fairchild Power Switch (FPS^™)

! AN-4137: Design Guidelines for Off-line Flyback

Converters Using Fairchild Power Switch (FPS^™)

! AN-4140: Transformer Design Consideration for

off-line Flyback Converters using Fairchild Power

Switch (FPS^™)

! AN-4141: Troubleshooting and Design Tips for

Fairchild Power Switch (FPS^™) Flyback Applications

! AN-4145: Electromagnetic Compatibility for Power

Converters

! AN-4147: Design Guidelines for RCD Snubber of

Flyback Converters

! AN-4148: Audible Noise Reduction Techniques for

FPS Applications

! AN-4150: Design Guidelines for Flyback Converters

Using FSQ-series Fairchild Power Switch (FPS^™)

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

Ordering Information

Maximum Output Power⁽¹⁾

230V_AC±15%⁽²⁾

85-265V_AC

Product

PKG.⁽⁵⁾

Number

Operating Current R_DS(ON)

Replaces

Devices

Temp.

Limit

Max.

Open

Adapter⁽³⁾

Frame⁽⁴⁾

FSCM0765R

FSDM07652RE

FSQ0765RSWDTU TO-220F-6L -25 to +85°C

2.5A

1.6Ω

80W

90W

48W

70W

Notes:

1. The junction temperature can limit the maximum output power.

2. 230V_ACor 100/115V_ACwith doubler.

3. Typical continuous power in a non-ventilated enclosed adapter measured at 50°C ambient temperature.

4. Maximum practical continuous power in an open-frame design at 50°C ambient.

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

2

Application Diagram

V_O

AC

IN

V_str

Drain

PWM

Sync

GND

V_CC

FB

FSQ0765R Rev.00

Figure 1. Typical Flyback Application

Internal Block Diagram

V_CC

3

V_str

6

Sync

5

Drain

1

OSC

AVS

V_CC

V_ref

0.35/0.55

V_Burst

V_CCgood

V_CC

V_ref

8V/12V

I_delay

I_FB

PWM

FB

4

3R

S

R

Q

Gate

driver

Soft-

Start

LEB

250ns

R

t

< t

OSP

ON

after SS

LPF

V

OSP

AOCP

2

S

R

Q

V

SD

V_OCP

(1.1V)

TSD

GND

Q

LPF

V_CC

V

OVP

V_CCgood

FSQ0765RS Rev.00

Figure 2. Internal Block Diagram

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

3

Pin Configuration

6. V_str

5. Sync

4. FB

3. V_CC

2. GND

1. Drain

FSQ0765R Rev.00

Figure 3. Pin Configuration (Top View)

Pin Definitions

Pin #

Name

Drain

GND

Description

1

2

SenseFET drain. High-voltage power SenseFET drain connection.

Ground. This pin is the control ground and the SenseFET source.

Power Supply. This pin is the positive supply input, providing internal operating current for

both startup and steady-state operation.

3

4

5

6

V_CC

Feedback. This pin is internally connected to the inverting input of the PWM comparator. The

collector of an opto-coupler is typically tied to this pin. For stable operation, a capacitor should

be placed between this pin and GND. If the voltage of this pin reaches 6V, the overload pro-

tection triggers, which shuts down the FPS.

FB

Sync. This pin is internally connected to the sync-detect comparator for quasi-resonant switch-

ing. In normal quasi-resonant operation, the threshold of the sync comparator is 1.2V/1.0V.

Sync

V_str

Startup. This pin is connected directly, or through a resistor, to the high-voltage DC link. At

startup, the internal high-voltage current source supplies internal bias and charges the exter-

nal capacitor connected to the V_CCpin. Once V_CCreaches 12V, the internal current source is

disabled. It is not recommended to connect V_strand Drain together.

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

4

Absolute Maximum Ratings

Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be opera-

ble above the recommended operating conditions and stressing the parts to these levels is not recommended. In addi-

tion, extended exposure to stresses above the recommended operating conditions may affect device reliability. The

absolute maximum ratings are stress ratings only. T_A= 25°C, unless otherwise specified.

Symbol

V_str

Parameter

Min.

500

Max.

Unit

V

V_strPin Voltage

Drain Pin Voltage

Supply Voltage

V_DS

650

V

V_CC

20

V

(5)

V_FB

Feedback Voltage Range

Sync Pin Voltage

-0.3

V_CC

V

V_Sync

I_DM

13.0

14.4

3.60

2.28

570

45

V

Drain Current Pulsed

A

T_C= 25°C

I_D

Continuous Drain Current⁽⁶⁾

A

T_C= 100°C

E_AS

P_D

Single Pulsed Avalanche Energy⁽⁷⁾

Total Power Dissipation (T_C=25°C)

Operating Junction Temperature

Operating Ambient Temperature

Storage Temperature

mJ

W

T_J

Internally limited

°C

T_A

-25

-55

+85

T_STG

+150

Human Body Model,

JESD22-A114

2.0

kV

Electrostatic Discharge

Protection

ESD

Charged Device Model,

JESD22-C101

Notes:

5. Guarenteed when external current applied to FB pin is lower than 100µA.

6. Repetitive rating: Pulse-width limited by maximum junction temperature.

7. L=81mH, starting T_J=25°C.

Thermal Impedance

T_A= 25°C unless otherwise specified.

Symbol

θ_JA

Parameter

Junction-to-Ambient Thermal Resistance⁽⁸⁾

Junction-to-Case Thermal Resistance⁽⁹⁾

Package

Value

50

Unit

°C/W

TO-220F-6L

θ_JC

2.8

Notes:

8. Free standing with no heat-sink under natural convection.

9. Infinite cooling condition - refer to the SEMI G30-88.

www.fairchildsemi.com

FSQ0765RS • Rev. 1.0.2

5

Electrical Characteristics

T_A= 25°C unless otherwise specified.

Symbol

Parameter

Conditions

Min. Typ. Max. Units

SENSEFET SECTION

BV_DSS

I_DSS

R_DS(ON)

C_OSS

t_d(on)

t_r

Drain Source Breakdown Voltage

Zero-Gate-Voltage Drain Current

Drain-Source On-State Resistance

Output Capacitance

V_CC= 0V, I_D= 100µA

650

V

µA

Ω

V_DS= 520V, V_GS= 0V

T_J= 25°C, I_D= 1.8A

300

1.6

1.3

125

27

V_GS= 0V, V_DS= 25V, f = 1MHz

pF

ns

Turn-On Delay Time

Rise Time

102

63

V_DD= 325V, I_D= 6.5A

t_d(off)

t_f

Turn-Off Delay Time

Fall Time

65

CONTROL SECTION

t_ON.MAXMaximum On Time

t_B

T_J= 25°C

8.8

10.0 11.2

µs

Blanking Time

T_J= 25°C, V_sync= 5V

T_J= 25°C, V_sync= 0V

13.2 15.0 16.8

6.0

t_W

Detection Time Window

Initial Switching Frequency

Switching Frequency Variation⁽¹¹⁾

µs

f_SW

59.6 66.7 75.8

kHz

%

Δf_SW

t_AVS

-25°C < T_J< 85°C

±5

±10

On Time

4.0

µs

at V_IN= 240V_DC, Lm = 360μH

(AVS triggered when

V_AVS>spec & t_AVS<spec.)

AVS Triggering

Threshold⁽¹¹⁾

Feedback

V_AVS

t_SW

1.2

V

Voltage

Sync = 500kHz sine input

V_FB= 1.2V, t_ON= 4.0µs

Switching Time Variance by AVS⁽¹¹⁾

13.5

700

20.5

µs

I_FB

D_MIN

Feedback Source Current

Minimum Duty Cycle

V_FB= 0V

900 1100

0

µA

%

V

V_START

V_STOP

t_S/S

11

7

12

8

13

9

UVLO Threshold Voltage

After turn-on

V

Internal Soft-Start Time

Over-Voltage Protection

With free-running frequency

17.5

19

ms

V

V_OVP

18

20

BURST-MODE SECTION

V_BURH

0.45 0.55 0.65

0.25 0.35 0.45

200

V

V_BURL

Burst-Mode Voltages

T_J= 25°C, t_PD= 200ns⁽¹⁰⁾

V_{B_HYS}

mV

Note:

10. Propagation delay in the control IC.

Continued on the following page...

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

6

Electrical Characteristics (Continued)

T_A= 25°C unless otherwise specified.

Symbol

Parameter

Conditions

Min. Typ. Max. Units

PROTECTION SECTION

I_LIMIT

V_SD

I_DELAY

t_LEB

Peak Current Limit

T_J= 25°C, di/dt = 460mA/µs

V_CC= 15V

2.20 2.50 2.80

A

V

Shutdown Feedback Voltage

Shutdown Delay Current

Leading-Edge Blanking Time⁽¹¹⁾

Threshold Time

5.5

4

6.0

5

6.5

6

V_FB= 5V

µA

ns

µs

250

1.2

t_OSP

1.4

T_J= 25°C

Output Short Threshold Feedback

Protection⁽¹¹⁾Voltage

OSP triggered when t_ON<t_OSP,

V_FB>V_OSP& lasts longer than

t_{OSP_FB}

V_OSP

1.8

2.0

V

t_{OSP_FB}

T_SD

Feedback Blanking Time

2.0

2.5

140

60

3.0

µs

Shutdown Temperature

Hysteresis

125

155

Thermal

°C

Shutdown⁽¹¹⁾

Hys

SYNC SECTION

V_SH1

1.0

0.8

1.2

1.0

230

4.7

4.4

1.4

1.2

Sync Threshold Voltage 1

Sync Delay Time^(11)(12)

V_CC= 15V, V_FB= 2V

V

ns

V

V_SL1

t_sync

V_SH2

V_SL2

4.3

4.0

5.1

4.8

Sync Threshold Voltage 2

Low Clamp Voltage

I_{SYNC_MAX}= 800µA

I_{SYNC_MIN}= 50µA

V_CLAMP

0.0

0.4

0.8

V

TOTAL DEVICE SECTION

Operating Supply Current

(Control Part Only)

I_OP

V_CC= 13V

1

3

5

mA

µA

V_CC= 10V

I_START

Start Current

350

450

550

(before V_CCreaches V_START

)

V_CC= 0V, V_STR= minimum

50V

I_CH

Startup Charging Current

0.65 0.85 1.00

26

mA

V

V_STR

Minimum V_STRSupply Voltage

Notes:

11.Guaranteed by design, but not tested in production.

12. Includes gate turn-on time.

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

7

Comparison Between FSDM0x65RNB and FSQ-Series

Function

FSDM0x65RE

FSQ-Series

FSQ-Series Advantages

! Improved efficiency by valley switching

! Reduced EMI noise

! Reduced components to detect valley point

Constant

Frequency PWM

Quasi-Resonant

Operation

Operation Method

! Valley switching

Reduce EMI Noise ! Inherent frequency modulation

! Alternate valley switching

Frequency

Modulation

EMI Reduction

Hybrid Control

CCM or AVS

Based on Load ! Improves efficiency by introducing hybrid control

and Input Condition

Advanced

Burst-Mode

Operation

Burst-Mode

Operation

Burst-Mode

Operation

! Improved standby power by AVS in burst-mode

! Improved reliability through precise AOCP

! Improved reliability through precise OSP

OLP, OVP,

AOCP, OSP

Strong Protections

TSD

OLP, OVP

! Stable and reliable TSD operation

! Converter temperature range

145°C without

Hysteresis

140°C with 60°C

Hysteresis

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

8

Typical Performance Characteristics

These characteristic graphs are normalized at T_A= 25°C.

1.2

1.0

0.8

0.6

0.4

0.2

0.0

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-25

0

25

50

75

100

125

-25

0

25

50

75

100

125

Temperature [°C]

Figure 13. Operating Supply Current (I_OP) vs. T_A

Figure 14. UVLO Start Threshold Voltage

(V_START) vs. T_A

1.2

1.0

0.8

0.6

0.4

0.2

0.0

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-25

0

25

50

75

100

125

-25

0

25

50

75

100

125

Temperature [°C]

Figure 15. UVLO Stop Threshold Voltage

(V_STOP) vs. T_A

Figure 16. Startup Charging Current (I_CH) vs. T_A

1.2

1.0

0.8

0.6

0.4

0.2

0.0

1.0

0.8

0.6

0.4

0.2

0.0

-25

0

25

50

75

100

125

-25

0

25

50

75

100

125

Temperature [°C]

Figure 17. Initial Switching Frequency (f_SW) vs. T_A

Figure 18. Maximum On Time (t_ON.MAX) vs. T_A

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

9

Typical Performance Characteristics (Continued)

These characteristic graphs are normalized at T_A= 25°C.

1.2

1.0

0.8

0.6

0.4

0.2

0.0

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-25

0

25

50

75

100

125

-25

0

25

50

75

100

125

Temperature [°C]

Figure 19. Blanking Time (t_B) vs. T_A

Figure 20. Feedback Source Current (I_FB) vs. T_A

1.2

1.0

0.8

0.6

0.4

0.2

0.0

1.0

0.8

0.6

0.4

0.2

0.0

-25

0

25

50

75

100

125

-25

0

25

50

75

100

125

Temperature [°C]

Figure 21. Shutdown Delay Current (I_DELAY) vs. T_A

Figure 22. Burst-Mode High Threshold Voltage

(V_burh) vs. T_A

1.2

1.0

0.8

0.6

0.4

0.2

0.0

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-25

0

25

50

75

100

125

-25

0

25

50

75

100

125

Temperature [°C]

Figure 23. Burst-Mode Low Threshold Voltage

(V_burl) vs. T_A

Figure 24. Peak Current Limit (I_LIM) vs. T_A

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

10

Typical Performance Characteristics (Continued)

These characteristic graphs are normalized at T_A= 25°C.

1.2

1.0

0.8

0.6

0.4

0.2

0.0

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-25

0

25

50

75

100

125

-25

0

25

50

75

100

125

Temperature [°C]

Figure 25. Sync High Threshold Voltage 1

(V_SH1) vs. T_A

Figure 26. Sync Low Threshold Voltage 1

(V_SL1) vs. T_A

1.2

1.0

0.8

0.6

0.4

0.2

0.0

1.0

0.8

0.6

0.4

0.2

0.0

-25

0

25

50

75

100

125

-25

0

25

50

75

100

125

Temperature [°C]

Figure 27. Shutdown Feedback Voltage (V_SD) vs. T_A

Figure 28. Over-Voltage Protection (V_OV) vs. T_A

1.2

1.0

0.8

0.6

0.4

0.2

0.0

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-25

0

25

50

75

100

125

-25

0

25

50

75

100

125

Temperature [°C]

Figure 29. Sync High Threshold Voltage 2

(V_SH2) vs. T_A

Figure 30. Sync Low Threshold Voltage 2

(V_SL2) vs. T_A

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

11

2.1 Pulse-by-Pulse Current Limit: Because current-

mode control is employed, the peak current through the

SenseFET is limited by the inverting input of PWM

comparator (V_FB*), as shown in Figure 23. Assuming

Functional Description

1. Startup: At startup, an internal high-voltage current

source supplies the internal bias and charges the

external capacitor (C_a) connected to the V_CCpin, as

that the 0.9mA current source flows only through the

internal resistor (3R + R = 2.8k), the cathode voltage of

diode D2 is about 2.5V. Since D1 is blocked when the

feedback voltage (V_FB) exceeds 2.5V, the maximum

illustrated in Figure 22. When V_CCreaches 12V, the

FPS™ begins switching and the internal high-voltage

current source is disabled. The FPS continues its normal

switching operation and the power is supplied from the

auxiliary transformer winding unless V_CCgoes below the

voltage of the cathode of D2 is clamped at this voltage,

clamping V_FB*. Therefore, the peak value of the current

stop voltage of 8V.

through the SenseFET is limited.

V_DC

2.2 Leading-Edge Blanking (LEB): At the instant the

internal SenseFET is turned on, a high-current spike

usually occurs through the SenseFET, caused by

primary-side capacitance and secondary-side rectifier

reverse recovery. Excessive voltage across the R_sense

C_a

V_CC

V_str

resistor would lead to incorrect feedback operation in the

current-mode PWM control. To counter this effect, the

FPS employs a leading-edge blanking (LEB) circuit. This

circuit inhibits the PWM comparator for a short time

(t_LEB) after the SenseFET is turned on in the Pulse-

3

6

I_CH

V_ref

8V/12V

V_CCgood

Width-Modulation (PWM) circuit.

Internal

Bias

3. Synchronization: The FSQ-series employs a quasi-

resonant switching technique to minimize the switching

noise and loss. The basic waveforms of the quasi-

resonant converter are shown in Figure 24. To minimize

the MOSFET's switching loss, the MOSFET should be

turned on when the drain voltage reaches its minimum

value, which is indirectly detected by monitoring the V_CC

FSQ0765R Rev.00

Figure 31. Startup Circuit

2. Feedback Control: FPS employs current-mode

control, as shown in Figure 23. An opto-coupler (such as

the FOD817A) and shunt regulator (such as the KA431)

are typically used to implement the feedback network.

Comparing the feedback voltage with the voltage across

the R_senseresistor makes it possible to control the

winding voltage, as shown in Figure 24.

V_ds

V_RO

switching duty cycle. When the reference pin voltage of

the shunt regulator exceeds the internal reference

voltage of 2.5V, the opto-coupler LED current increases,

pulling down the feedback voltage and reducing the duty

cycle. This typically happens when the input voltage is

increased or the output load is decreased.

V_RO

V_DC

t_F

V_sync

V_ovp(8V)

V_ref

V_CC

I_delay

I_FB

1.2V

V_FB

V_O

SenseFET

1.0V

OSC

4

FOD817A

D1

D2

C_B

3R

R

230ns Delay

+

Gate

MOSFET Gate

ON

V_FB

*

driver

KA431

-

ON

OLP

R_sense

V_SD

FSQ0765R Rev.00

FSQ0765R Rev. 00

Figure 33. Quasi-Resonant Switching Waveforms

Figure 32. Pulse-Width-Modulation (PWM) Circuit

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

12

The switching frequency is the combination of blank time

(t ) and detection time window (t ). In case of a heavy

t_X

t_B=15μs

B

W

load, the sync voltage remains flat after t and waits for

B

valley detection during t . This leads to a low switching

W

frequency not suitable for heavy loads. To correct this

drawback, additional timing is used. The timing

conditions are described in Figures 25, 26, and 27. When

I_DS

the V

remains flat higher than 4.4V at the end of t

sync

B

V_DS

which is instant t , the next switching cycle starts after

X

internal delay time from t . In the second case, the next

X

ingnore

switching occurs on the valley when the V

goes below

sync

4.4V

4.4V within t . Once V

detects the first valley in t , the

B

sync

V_sync

1.2V

1.0V

other switching cycle follows classical QRC operation.

internal delay

FSQ0765R Rev. 00

t_X

t_B=15μs

Figure 36. After V_syncFinds First Valley

I_DS

4. Protection Circuits: The FSQ-series has several

self-protective functions, such as Overload Protection

(OLP), Abnormal Over-Current Protection (AOCP),

Over-Voltage Protection (OVP), and Thermal Shutdown

(TSD). All the protections are implemented as auto-

restart mode. Once the fault condition is detected,

switching is terminated and the SenseFET remains off.

This causes V_CCto fall. When V_CCfalls down to the

V_DS

4.4V

V_sync

Under-Voltage Lockout (UVLO) stop voltage of 8V, the

protection is reset and the startup circuit charges the

V_CCcapacitor. When the V_CCreaches the start voltage

1.2V

1.0V

internal delay

FSQ0765R Rev. 00

of 12V, normal operation resumes. If the fault condition is

not removed, the SenseFET remains off and V_CCdrops

Figure 34. V_sync> 4.4V at t_X

to stop voltage again. In this manner, the auto-restart can

alternately enable and disable the switching of the power

SenseFET until the fault condition is eliminated.

Because these protection circuits are fully integrated into

the IC without external components, the reliability is

improved without increasing cost.

t_X

t_B=15μs

Fault

occurs

Fault

removed

Power

on

V_DS

I_DS

V_DS

V_CC

4.4V

12V

8V

V_sync

1.2V

1.0V

t

internal delay

FSQ0765R Rev. 00

Normal

operation

Fault

situation

Normal

operation

FSQ0765R Rev. 00

Figure 35. V_sync< 4.4V at t_X

Figure 37. Auto-Restart Protection Waveforms

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

13

4.1 Overload Protection (OLP): Overload is defined as

the load current exceeding its normal level due to an

unexpected abnormal event. In this situation, the

protection circuit should trigger to protect the SMPS.

However, even when the SMPS is in the normal

operation, the overload protection circuit can be

triggered during the load transition. To avoid this

undesired operation, the overload protection circuit is

designed to trigger only after a specified time to

determine whether it is a transient situation or a true

overload situation. Because of the pulse-by-pulse

current limit capability, the maximum peak current

through the SenseFET is limited, and therefore the

maximum input power is restricted with a given input

voltage. If the output consumes more than this maximum

power, the output voltage (V_O) decreases below the set

3R

R

OSC

PWM

S

R

Q

Gate

driver

LEB

250ns

R_sense

+

-

2

AOCP

FSQ0765R Rev.00

GND

V_OCP

Figure 39. Abnormal Over-Current Protection

4.3 Output-Short Protection (OSP): If the output is

shorted, steep current with extremely high di/dt can flow

through the SenseFET during the LEB time. Such a

steep current brings high voltage stress on drain of

SenseFET when turned off. To protect the device from

such an abnormal condition, OSP is included in the FSQ-

voltage. This reduces the current through the opto-

coupler LED, which also reduces the opto-coupler

transistor current, thus increasing the feedback voltage

(V_FB). If V_FBexceeds 2.5V, D1 is blocked and the 5µA

current source starts to charge CB slowly up to V_CC. In

this condition, V_FBcontinues increasing until it reaches

series. It is comprised of detecting V and SenseFET

FB

turn-on time. When the V is higher than 2V and the

FB

6V, when the switching operation is terminated, as

shown in Figure 29. The delay time for shutdown is the

time required to charge C_FBfrom 2.5V to 6V with 5µA. A

SenseFET turn-on time is lower than 1.2µs, the FPS

recognizes this condition as an abnormal error and shuts

down PWM switching until V

reaches V

again. An

CC

start

20 ~ 50ms delay time is typical for most applications.

abnormal condition output short is shown in Figure 31.

Rectifier

Diode

Current

Turn-off delay

MOSFET

Drain

Current

FSQ0765R Rev.00

V_FB

Overload protection

6.0V

I_LIM

V_FB

0

Minimum turn-on time

D

2.5V

V_o

1.2μs

output short occurs

t₁₂= C_FB*(6.0-2.5)/I_delay

0

t₁

t₂

t

I_o

FSQ0765R Rev. 00

Figure 38. Overload Protection

0

Figure 40. Output Short Waveforms

4.2 Abnormal Over-Current Protection (AOCP): When

the secondary rectifier diodes or the transformer pins are

shorted, a steep current with extremely high di/dt can

flow through the SenseFET during the LEB time. Even

though the FSQ-series has overload protection, it is not

enough to protect the FSQ-series in that abnormal case,

since severe current stress is imposed on the SenseFET

until OLP triggers. The FSQ-series has an internal

AOCP circuit shown in Figure 30. When the gate turn-on

signal is applied to the power SenseFET, the AOCP

block is enabled and monitors the current through the

sensing resistor. The voltage across the resistor is

compared with a preset AOCP level. If the sensing

resistor voltage is greater than the AOCP level, the set

signal is applied to the latch, resulting in the shutdown of

the SMPS.

4.4 Over-Voltage Protection (OVP): If the secondary-

side feedback circuit malfunctions or a solder defect

caused an open in the feedback path, the current

through the opto-coupler transistor becomes almost

zero. Then, V_FBclimbs up in a similar manner to the

overload situation, forcing the preset maximum current

to be supplied to the SMPS until overload protection is

activated. Because more energy than required is

provided to the output, the output voltage may exceed

the rated voltage before overload protection is activated,

resulting in the breakdown of the devices in the

secondary side. To prevent this situation, an over-voltage

protection (OVP) circuit is employed. In general, V_CCis

proportional to the output voltage and the FSQ-series

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

14

uses V_CCinstead of directly monitoring the output

voltage. If V_CCexceeds 19V, an OVP circuit is activated

V_O

set

V_O

resulting in the termination of the switching operation. To

avoid undesired activation of OVP during normal

operation, V_CCshould be designed to be below 19V.

V_FB

0.55V

0.35V

4.5 Thermal Shutdown with Hysteresis (TSD): The

SenseFET and the control IC are built in one package.

This enables the control IC to detect the abnormally high

temperature of the SenseFET. If the temperature

exceeds approximately 140°C, the thermal shutdown

triggers IC shutdown. The IC recovers its operation when

the junction temperature decreases 60°C from TSD

temperature and V_CCreaches startup voltage (V_start).

I_DS

V_DS

5. Soft-Start: The FPS has an internal soft-start circuit

that increases PWM comparator inverting input voltage

with the SenseFET current slowly after it starts up. The

typical soft-start time is 17.5ms. The pulse width to the

power-switching device is progressively increased to

establish the correct working conditions for transformers,

inductors, and capacitors. The voltage on the output

capacitors is progressively increased with the intention of

smoothly establishing the required output voltage. This

mode helps prevent transformer saturation and reduces

stress on the secondary diode during startup.

time

Switching

disabled

Switching

disabled

t4

t2 t3

t1

FSQ0765R Rev.00

Figure 41. Waveforms of Burst Operation

7. Switching Frequency Limit: To minimize switching

loss and Electromagnetic Interference (EMI), the

MOSFET turns on when the drain voltage reaches its

minimum value in quasi-resonant operation. However,

this causes switching-frequency to increases at light-

load conditions. As the load decreases or input voltage

increases, the peak drain current diminishes and the

switching frequency increases. This results in severe

switching losses at light-load condition, as well as

intermittent switching and audible noise. These problems

create limitations for the quasi-resonant converter

topology in a wide range of applications.

6. Burst Operation: To minimize power dissipation in

standby mode, the FPS enters burst-mode operation. As

the load decreases, the feedback voltage decreases. As

shown in Figure 32, the device automatically enters

burst-mode when the feedback voltage drops below

V_BURL(350mV). At this point, switching stops and the

output voltages start to drop at a rate dependent on

standby current load. This causes the feedback voltage

to rise. Once it passes V_BURH(550mV), switching

To overcome these problems, FSQ-series employs a

frequency-limit function, as shown in Figures 34 and 35.

Once the SenseFET is turned on, the next turn-on is

prohibited during the blanking time (t_B). After the

resumes. The feedback voltage then falls and the

process repeats. Burst-mode operation alternately

enables and disables switching of the power SenseFET,

thereby reducing switching loss in standby mode.

blanking time, the controller finds the valley within the

detection time window (t_W) and turns on the MOSFET, as

shown in Figures 33 and Figure 34 (Cases A, B, and C).

If no valley is found during t_W, the internal SenseFET is

forced to turn on at the end of t_W(Case D). Therefore,

the devices have a minimum switching frequency of

48kHz and a maximum switching frequency of 67kHz.

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

15

8. AVS (Alternating Valley Switching): Due to the

quasi-resonant operation with limited frequency, the

switching frequency varies depending on input voltage,

load transition, and so on. At high input voltage, the

switching on time is relatively small compared to low

input voltage. The input voltage variance is small and the

switching-frequency modulation width becomes small. To

improve the EMI performance, AVS is enabled when

input voltage is high and the switching on time is small.

t_s^max=21μs

I_DS

A

t_B=15μs

t_s

I_DS

Internally, quasi-resonant operation is divided into two

categories; one is first valley switching and the other is

second-valley switching after blanking time. In AVS, two

successive occurrences of first-valley switching and the

other two successive occurrences of second-valley

switching is alternatively selected to maximize frequency

modulation. As depicted in Figure 34, the switching

frequency hops when the input voltage is high. The

internal timing diagram of AVS is described in Figure 35.

B

t_B=15μs

t_s

I_DS

f_s

1

μ

Assume the resonant period is 2 s

C

15μs

67kHz

59kHz

1

t_B=15μs

17μs

53kHz

48kHz

1

t_s

19μs

AVS trigger point

Constant

frequency

1

Variable frequency within limited range

DCM

21μs

CCM

I_DS

AVS region

D

C

B

A

t_B=15μs

t_W=6μs

V

in

FSQ0765R Rev.00

t_s^max=21μs

FSQ0765R Rev. 00

Figure 42. QRC Operation with Limited Frequency

Figure 43. Switching Frequency Range

V_gate

V_gatecontinued 2 pulses

V_gatecontinued another 2 pulses

1st valley switching

2nd valley switching

1st valley switching

GateX2

fixed

fixed fixed

One-shot

AVS

triggering

de-triggering

1st or 2nd is depend on GateX2

triggering

1st or 2nd is dependent on GateX2

V_DS

t_B

GateX2: Counting V_gateevery 2 pulses independent on other signals.

FSQ0765R Rev. 00

1st valley- 2nd valley frequency modulation.

Modulation frequency is approximately 17kHz.

Figure 44. Alternating Valley Switching (AVS)

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

16

PCB Layout Guide

Due to the combined scheme, FPS shows better noise

immunity than a conventional PWM controller and

MOSFET discrete solution. Furthermore, internal drain

current sense eliminates noise generation caused by a

sensing resistor. There are some recommendations for

PCB layout to enhance noise immunity and suppress the

noise inevitable in power-handling components.

There are typically two grounds in the conventional

SMPS: power ground and signal ground. The power

ground is the ground for primary input voltage and

power, while the signal ground is the ground for PWM

controller. In FPS, those two grounds share the same

pin, GND. Normally the separate grounds do not share

the same trace and meet only at one point, the GND pin.

Moreover, wider patterns for both grounds decrease

resistance for large currents.

Capacitors at the V_CCand FB pins should be as close as

possible to the corresponding pins to avoid noise from

the switching device. Sometimes Mylar® or ceramic

capacitors with electrolytic for V_CCare better for smooth

operation. The ground of these capacitors needs to

connect to the signal ground (not power ground).

Figure 45. Recommended PCB Layout

The cathode of the snubber diode should be close to the

drain pin to minimize stray inductance. The Y-capacitor

between primary and secondary should be directly

connected to the power ground of DC link to maximize

surge immunity.

Because the voltage range of feedback and sync line is

small, it is affected by the noise of the drain pin. Those

traces should not draw across or close to the drain line.

When the heat sink is connected to the ground, it should

be connected to the power ground. If possible, avoid

using jumper wires for power ground and drain.

Mylar® is a registered trademark of DuPont Teijin Films.

FSQ0765RS • Rev. 1.0.2

www.fairchildsemi.com

17

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1


型号：	FSQ0765RSWDTU
厂家：	ONSEMI
描述：	具有准谐振运行功能的 650V 集成电源开关，适用于 70W 离线反激转换器局域网开关电源开关转换器
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中文：	中文翻译
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FSQ0765RSWDTU [ONSEMI]

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