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FAN6754 Schematic ( PDF Datasheet ) - Fairchild Semiconductor

Teilenummer FAN6754
Beschreibung Highly Integrated Green-Mode PWM Controller
Hersteller Fairchild Semiconductor
Logo Fairchild Semiconductor Logo 




Gesamt 14 Seiten
FAN6754 Datasheet, Funktion
September 2009
FAN6754
Highly Integrated Green-Mode PWM Controller
Brownout and Constant Power Limited by HV Pin
Features
ƒ High-Voltage Startup
ƒ AC Input Brownout Protection with Hysteresis
ƒ Low Operating Current: 1.7mA
ƒ Linearly Decreasing PWM Frequency to 22KHz
ƒ Frequency Hopping to Reduce EMI Emission
ƒ Fixed PWM Frequency: 65KHz
ƒ Peak-Current-Mode Control
ƒ Cycle-by-Cycle Current Limiting
ƒ Leading-Edge Blanking (LEB)
ƒ Internal Open-Loop Protection
ƒ GATE Output Maximum Voltage Clamp: 13V
ƒ VDD Under-Voltage Lockout (UVLO)
ƒ VDD Over-Voltage Protection (OVP)
ƒ Programmable Over-Temperature Protection (OTP)
ƒ Internal Latch Circuit (OVP, OTP)
ƒ Open-Loop Protection (OLP); Restart for MR, Latch
for ML
www.DataShƒeet4BUu.cioltm-in 8ms Soft-Start Function
ƒ Constant Power Limit (Full AC Input Range)
ƒ Internal OTP Sensor with Hysteresis
Applications
General-purpose switch-mode power supplies and
flyback power converters, including:
ƒ Power Adapters
Description
The highly integrated FAN6754 PWM controller
provides several features to enhance the performance
of flyback converters. To minimize standby power
consumption, a proprietary green-mode function
provides off-time modulation to continuously decrease
the switching frequency under light-load conditions.
Under zero-load and very light-load conditions,
FAN6754 saves PWM pulses by entering deep burst
mode. This burst mode function enables the power
supply to meet international power conservation
requirements.
FAN6754 integrates a frequency-hopping function
internally to reduce EMI emission of a power supply
with minimum line filters. Built-in synchronized slope
compensation is accomplished by, proprietary internal
compensation for constant output power limit over
universal AC input range. Also, the gate output is
clamped at 13V to protect the external MOSFET from
over-voltage damage.
Other protection functions include AC input brownout
protection with hysteresis and VDD over-voltage
protection. For over-temperature protection, an external
NTC thermistor can be applied to sense the external
switcher’s temperature. When VDD OVP or OTP are
activated, an internal latch circuit is used to latch-off the
controller. The latch mode is reset when the VDD supply
is removed.
FAN6754 is available in an 8-pin SOP package.
Ordering Information
Part Number
Operating
Temperature Range
FAN6754MRMY
FAN6754MLMY
-40 to +105°C
-40 to +105°C
Eco
Status
RoHS
RoHS
Package
8-Pin, Small Outline Package (SOP)
8-Pin, Small Outline Package (SOP)
Packing Method
Tape & Reel
Tape & Reel
For Fairchild’s definition of Eco Status, please visit: http://www.fairchildsemi.com/company/green/rohs_green.html.
© 2009 Fairchild Semiconductor Corporation
FAN6754 • Rev. 1.0.0
www.fairchildsemi.com






FAN6754 Datasheet, Funktion
Typical Performance Characteristics
Figure 5. Brownout Circuit
www.DataSheet4U.com
Figure 6. Brownout Behavior
© 2009 Fairchild Semiconductor Corporation
FAN6754 • Rev. 1.0.0
Figure 7. VDD-AC and AC Recovery
6
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6 Page









FAN6754 pdf, datenblatt
The HV pin can perform current limit to shrink the
tolerance of OCP (Over-Current Protection) under full
range of AC voltage, to linearly current limit curve as
shown in Figure 25.
level by half to lower
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heavy-load efficiency.
0.47
0.46
0.45
0.44
0.43
0.42
0.41
0.4
0.39
0.38
100 120 140 160 180 200 220 240 260 280 300 320 340 360 380
DC Voltage on HV Pin (V)
Figure 25. Linearly Current Limit Curve
VDD Over-Voltage Protection (OVP)
VDD over-voltage protection prevents damage due to
abnormal conditions. If the VDD voltage is over the over-
voltage protection voltage (VDD-OVP) and lasts for tD-
VDDOVP, the PWM pulses are disabled until the VDD
voltage drops below the UVLO, then starts again. Over-
voltage conditions are usually caused by open feedback
loops.
Thermal Protection
An NTC thermistor, RNTC, in series with resistor RA, can
be connected from the RT pin to ground. A constant
current IRT is output from the RT pin. The voltage on the
RT pin can be expressed as VRT= IRT • (RNTC + RPTC),
where IRT is 100µA. At high ambient temperature, RNTC
is smaller, such that VRT decreases. When VRT is less
than 1.035V (VRTTH1), the PWM turns off after 16ms
(tD-OTP1). If VRT is less than 0.7V (VRTTH2), PWM turns off
after 185µs (tD-OTP2).
Limited Power Control
The FB voltage increases every time the output of the
power supply is shorted or overloaded. If the FB voltage
remains higher than a built-in threshold for longer than
tD-OLP, PWM output is turned off. As PWM output is
turned off, VDD begins decreasing.
When VDD goes below the turn-off threshold (9V) the
controller is totally shut down and, VDD is continuously
discharged to VDD-OLP (6.5V) by IDD-OLP to lower the
average input power. This is called two-level UVLO. VDD
is cycled again. This protection feature continues as
long as the overloading condition persists. This
prevents the power supply from overheating due to
overloading conditions.
Noise Immunity
Noise on the current sense or control signal may cause
significant pulse-width jitter, particularly in continuous-
conduction mode. Slope compensation helps alleviate
this problem. Good placement and layout practices
should be followed. Avoiding long PCB traces and
component leads, locating compensation and filter
components near the FAN6754, and increasing the
power MOS gate resistance improve performance.
www.DataSheet4U.com
© 2009 Fairchild Semiconductor Corporation
FAN6754 • Rev. 1.0.0
12
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