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Q0765RQ Schematic ( PDF Datasheet ) - Fairchild Semiconductor

Teilenummer Q0765RQ
Beschreibung FSQ0765RQ
Hersteller Fairchild Semiconductor
Logo Fairchild Semiconductor Logo 




Gesamt 19 Seiten
Q0765RQ Datasheet, Funktion
April 2009
FSQ0765RQ
Green-Mode Fairchild Power Switch (FPS™) for
Quasi-Resonant Operation - Low EMI and High Efficiency
Features
! Optimized for Quasi-Resonant Converter (QRC)
! Low EMI through Variable Frequency Control and AVS
(Alternating Valley Switching)
! 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 Offline Forward
Converters Using Fairchild Power Switch (FPS)
! AN-4137: Design Guidelines for Offline Flyback
Converters Using Fairchild Power Switch (FPS)
! AN-4140: Transformer Design Consideration for
Offline 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
! AN-4148: Audible Noise Reduction Techniques for
Fairchild Power Switch Fairchild Power Switch(FPS™)
Applications
! AN-4150: Design Guidelines for Flyback Converters
Using FSQ-Series Fairchild Power Switch (FPS)
Description
A Quasi-Resonant Converter (QRC) generally shows
lower EMI and higher power conversion efficiency than a
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 that is well suited
for cost-effective designs of quasi-resonant switching
flyback converters.
© 2008 Fairchild Semiconductor Corporation
FSQ0765RQ Rev. 1.0.1
www.fairchildsemi.com
Free Datasheet http://www.datasheet4u.com/






Q0765RQ Datasheet, Funktion
Electrical Characteristics
TA = 25°C unless otherwise specified.
Symbol
Parameter
SENSEFET SECTION
BVDSS Drain Source Breakdown Voltage
IDSS Zero-Gate-Voltage Drain Current
RDS(ON) Drain-Source On-State Resistance
COSS Output Capacitance
td(on)
Turn-On Delay Time
tr Rise Time
td(off)
Turn-Off Delay Time
tf Fall Time
CONTROL SECTION
tON.MAX
tB
tW
fS
ΔfS
tAVS
VAVS
Maximum On Time
Blanking Time
Detection Time Window
Initial Switching Frequency
Switching Frequency Variation(11)
AVS Triggering
Threshold(11)
On Time
Feedback
Voltage
tSW Switching Time Variance by AVS(11)
IFB Feedback Source Current
DMIN
Minimum Duty Cycle
VSTART
VSTOP
UVLO Threshold Voltage
tS/S Internal Soft-Start Time
BURST-MODE SECTION
VBURH
VBURL
Hysteresis
Burst-Mode Voltages
Note:
10. Propagation delay in the control IC.
Condition
Min. Typ. Max. Unit
VCC = 0V, ID = 100µA
VDS = 520V, VGS = 0V
TJ = 25°C, ID = 1.8A
VGS = 0V, VDS = 25V, f = 1MHz
VDD = 325V, ID = 6.5A
650
300
1.3 1.6
125
27
102
63
65
V
µA
Ω
pF
ns
ns
ns
ns
TJ = 25°C
TJ = 25°C, Vsync = 5V
TJ = 25°C, Vsync = 0V
-25°C < TJ < 85°C
at VIN = 240VDC, Lm = 360μH
(AVS triggered when VAVS>spec
& tAVS<spec.)
Sync = 500kHz sine input
VFB = 1.2V, tON = 4.0µs
VFB = 0V
VFB = 0V
After turn-on
With free-running frequency
8.8 10.0 11.2
13.5 15.0 16.5
6.0
59.6 66.7 75.8
±5 ±10
4.0
1.2
13.5 20.5
700 900 1100
0
11 12 13
789
17.5
µs
µs
µs
kHz
%
µs
V
µs
µA
%
V
V
ms
TJ = 25°C, tPD = 200ns(10)
0.45 0.55 0.65
0.25 0.35 0.45
200
V
V
mV
Continued on the following page...
© 2008 Fairchild Semiconductor Corporation
FSQ0765RQ Rev. 1.0.1
6
www.fairchildsemi.com
Free Datasheet http://www.datasheet4u.com/

6 Page









Q0765RQ pdf, datenblatt
Functional Description
1. Startup: At startup, an internal high-voltage current
source supplies the internal bias and charges the
external capacitor (Ca) connected to the VCC pin, as
illustrated in Figure 22. When VCC reaches 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 VCC goes below the
stop voltage of 8V.
VDC
Ca
VCC
3
6 Vstr
8V/12V
FSQ0765R Rev.00
VCC good
ICH
Vref
Internal
Bias
Figure 22. 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 Rsense resistor makes it possible to control the
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.
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 (VFB*), as shown in Figure 23. Assuming
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 (VFB) exceeds 2.5V, the maximum
voltage of the cathode of D2 is clamped at this voltage,
clamping VFB*. Therefore, the peak value of the current
through the SenseFET is limited.
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 Rsense
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
(tLEB) after the SenseFET is turned on.
VCC Vref
Idelay
IFB
VO
VFB
4
OSC
FOD817A
D1 D2
CB 3R
KA431
+
VFB*
-
R
SenseFET
Gate
driver
FSQ0765R Rev. 00
VSD
OLP
Rsense
Figure 23. Pulse-Width-Modulation (PWM) Circuit
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 VCC
winding voltage, as shown in Figure 24.
Vds
VDC
VRO
VRO
Vsync
tF
Vovp (8V)
1.2V
MOSFET Gate
1.0V
230ns Delay
ON ON
FSQ0765R Rev.00
Figure 24. Quasi-Resonant Switching Waveforms
© 2008 Fairchild Semiconductor Corporation
FSQ0765RQ Rev. 1.0.1
12
www.fairchildsemi.com
Free Datasheet http://www.datasheet4u.com/

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