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PDF FAN6751 Data sheet ( Hoja de datos )
| Número de pieza | FAN6751 | |
| Descripción | Highly Integrated Green-Mode PWM Controller | |
| Fabricantes | Fairchild Semiconductor | |
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www.fairchildsemi.com
AN-6073
FAN6751 — Highly Integrated Green-Mode PWM Controller
Introduction
This application note describes a detailed design strategy for
a high-efficiency, compact flyback converter. Design
considerations and mathematical equations are presented as
well as guidelines for a printed circuit board layout. The
highly integrated FAN6751 series of PWM controllers
provides several features to enhance the performance for
LCDM/TV, NB, and adapters.
The green-mode function includes off-time modulation and
burst mode to reduce the PWM frequency at light-load and
in no-load conditions. To avoid acoustic noise problems, the
minimum PWM frequency is set above 18KHz. This green-
mode function enables the power supply to meet
international power conservation requirements. With the
internal high-voltage startup circuitry, the power loss due to
bleeding resistors is also eliminated. Built-in synchronized
slope compensation achieves stable peak-current-mode
control. The proprietary external line compensation ensures
constant output power limit over a wide AC input voltage
range, from 90VAC to 264VAC.
FAN6751 provides many protection functions, as shown in
Table 1. In addition to cycle-by-cycle current limiting, the
internal open-loop protection circuit ensures safety should
an open-loop or output short-circuit failure occur.
Features
High-Voltage Startup
Low Operating Current: 4mA
Linearly Decreasing PWM Frequency to 18KHz
Fixed PWM Frequency: 65KHz
Peak-Current-Mode Control
Cycle-by-Cycle Current Limiting
Leading-Edge Blanking (LEB)
Synchronized Slope Compensation
Internal Open-loop Protection
GATE Output Maximum Voltage Clamp: 18V
VDD Under-Voltage Lockout (UVLO)
VDD Over-Voltage Protection (OVP)
Internal Recovery Circuit (OVP, OLP)
Internal Sense Short-Circuit Protection
External Constant Power Limit (Full AC Input Range)
Internal OTP Sensor with Hysteresis
Built-in 5ms Soft-Start Function
Built-in VIN Pin Pull HIGH (> 4.7V) Recovery
Function for Second-Side Output OVP
Brownout Protection with Hysteresis
Applications
General-purpose, switch-mode power supplies and flyback
power converters, including:
Power Adapters
Open-frame SMPS
LCD Monitor/TV
SOP-8
GND
FB
NC
HV
1
2
3
4
8 GATE
7 VDD
6 SENSE
5 VIN
Figure 1. Pin Configuration (Top View)
Table 1. Protection Functions of FAN6751 Series
Part Number
FAN6751MRMY
FAN6751HLMY
OVP (VDD)
Recovery
Latch
OLP (FB)
Recovery
Latch
Pull-High
Protection (VIN)
Recovery
Latch
© 2008 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 9/26/08
OTP
(Internal)
Recovery
Recovery
SCP
(SENSE)
Recovery
Recovery
PWM
Frequency
65KHz
100KHz
www.fairchildsemi.com
Free Datasheet http://www.datasheet4u.com/
1 page  
AN-6073
Figure 11. FAN6751HL Burst-mode Operation
VO
APPLICATION NOTE
larger ripple current ratings are required. DCM operation
also results in a higher output voltage spike. A large LC
filter is added. Therefore, a flyback converter in CCM
achieves better performance with lower component cost.
Despite the above advantages of CCM operation, there is
one concern—stability. In CCM operation, the output power
is proportional to the average inductor current, while the
peak current remains controlled. This causes sub-harmonic
oscillation when the PWM duty cycle exceeds 50%. Adding
slope compensation (reducing the current-loop gain) is an
effective way to prevent oscillation. The FAN6751
introduces a synchronized positive-going ramp (VSLOPE) in
every switching cycle to stabilize the current loop.
Therefore, the FAN6751 can be used to design a cost-
effective, highly efficient, compact flyback power supply
operating in CCM without additional external components.
The positive ramp added is:
VSLOPE = VSL • D
where VSL = 0.33V and D = duty cycle.
(4)
VFB
1.1
Ids
Vds
Figure 13. Synchronized Slope Compensation
time
Switching Switching Switching Switching
Disabled Disabled Disabled Disabled
Figure 12. FAN6751MR Burst-Mode Operation
Built-in Slope Compensation
A flyback converter can be operated in either discontinuous
current mode (DCM) or continuous current mode (CCM).
There are many advantages when operating the converter in
CCM. With the same output power, a converter in CCM
exhibits a smaller peak inductor current than in DCM.
Therefore, a small-sized transformer and a low-rated
MOSFET can be applied. On the secondary side of the
transformer, the RMS output current of DCM can be twice
that of CCM. Larger wire gauge and output capacitors with
Over-Power Compensation
The maximum output power of a flyback converter can
generally be designed by the current-sense resistor RS. When
the load increases, the peak inductor current increases
accordingly. As the current-sense signal of the SENSE pin
exceeds the internal limit VSENSE, 0.83V typically, as
VIN=1V, FAN6751 stops the PWM pulse immediately. The
output power of a flyback power supply in DCM is
calculated as follows:
POUT
=
1
2 • LP
• IPK 2 • fS
•η
where:
Lp is the transformer primary-side inductance;
IPK is the peak inductor current;
fS is the PWM frequency; and
η is the conversion efficiency.
(5)
© 2008 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 9/26/08
5
www.fairchildsemi.com
Free Datasheet http://www.datasheet4u.com/
5 Page 
AN-6073
Table 3. Experimental Results
Input Voltage
90V/60Hz
264V/50Hz
Input Wattage (No load)
0.198W
0.277W
Table 4. 44W LCD Monitor Evaluation Board Part List
PART#
F1
NTC1
R1, R2
R3
R4
R5, R6, R7, R8
R9
R10
R11
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22
R23
R24
R25
R26
R29
R30
R31
R32
U1
U2
U3
U4
M1
VALUE
Fuse
4A/250V
NTC
5Ω
Resistor
1MΩ
10MΩ
47KΩ
47Ω
2KΩ
0Ω
NC
130KΩ
51KΩ
10Ω
0Ω
100KΩ
22KΩ
10KΩ
15Ω
100Ω
100Ω
0.5Ω
750Ω
4.7KΩ
120KΩ
15KΩ
10KΩ
1KΩ
1KΩ
1KΩ
IC
FAN6751MR
PC817
PC817
TL431
TNR
470V
NOTE
Glass
1206+/-5%
1206 +/-5%
2W +/-5%
1206+/-5%
0805 +/-5%
0805 +/-5%
2W +/-5%
2W +/-5%
0805+/-5%
1206+/-5%
1206+/-5%
1/4W
0805
5µH,1/2W
1/4W
0805+/-5%
1W
0805+/-5%
0805+/-5%
0805+/-5%
0805+/-5%
1206+/-5%
0805+/-5%
0805+/-5%
0805+/-5%
Fairchild
Fairchild
Fairchild
Fairchild
7ψ
PART#
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
D1
D2
D3
D4
D5
ZD1
ZD2
BD1
Q1
L1
L2
L3
APPLICATION NOTE
Output Current Protection (5V)
5.8A
5.1A
VALUE
Capacitor
2.2nF/250V
2.2nF/250V
0.33µF/250V
0.22µF/250V
120µF/400V
10nF /1KV
2.2nF /250V
2.2nF
1nF
1nF
1000µF/16V
1000µF/16V
0.1µF/50V
0.1µF/50V
0.1µF/50V
4.7µF/50V
2200µF/10V
1000µF/10V
470pF
10µF/50V
0.1µF
Diode
STPS20H100CT
1N4148
FR107
FR103
MBR2060CT
6.8V
15V
KBP206G
MOSFET
FQP8N60C
Filter
9mH
2.7µH
2.7µH
NOTE
Y2, Ceramic
Y2, Ceramic
Box Capacitor
Box Capacitor
Electrolytic
Ceramic
Ceramic
1206
1206
1206
Electrolytic
Electrolytic
1206
1206
1206
Electrolytic
Electrolytic
Electrolytic
0805
Electrolytic
0805
100V/20A
60V/20A
Fairchild
© 2008 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 9/26/08
11
www.fairchildsemi.com
Free Datasheet http://www.datasheet4u.com/
11 Page | ||
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| PDF Descargar | [ Datasheet FAN6751.PDF ] | |
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