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PDF NCP1280DR2 Data sheet ( Hoja de datos )
| Número de pieza | NCP1280DR2 | |
| Descripción | Active Clamp Voltage Mode PWM Controller for Off-Line Applications | |
| Fabricantes | ON | |
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NCP1280
Active Clamp Voltage Mode
PWM Controller for Off−Line
Applications
The NCP1280 provides a highly integrated solution for off−line
power supplies requiring high−efficiency and low parts count. This
voltage mode controller provides control outputs for driving a forward
converter primary MOSFET and an auxiliary MOSFET for active
clamp circuit. The second output with its programmable delay can also
be used for driving a synchronous rectifier on the secondary or for
asymmetric half bridge circuits. Incorporation of high voltage start−up
circuitry (with 700 V capability) reduces parts count and system
power dissipation. Additional features such as line UV/OV protection,
soft start, single resistor programmable (high) frequency oscillator,
line voltage feedforward, dual mode overcurrent protection and
maximum duty cycle control, allow converter optimization at minimal
cost. Compared to a traditional forward converter, an NCP1280 based
converter can offer significant efficiency improvements and system
cost savings.
Features
• Internal High Voltage Start−Up Regulator (25 V to 700 V)
• Dual Control Outputs with Adjustable Overlap Delay
• Programmable Maximum Duty Cycle Control
• Single Resistor Oscillator Frequency Setting
• Fast Line Feedforward
• Line Under/Overvoltage Lockout
• Dual Mode Overcurrent Protection
• Programmable Soft Start
• Precision 5.0 V Reference
Typical Applications
• Off−Line Power Converters in 100−500 W Range
• Desktop Power Supplies (High−End)
• Industrial Power Supplies
• Plasma/LCD TV Front−End
TX1
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MARKING
DIAGRAM
16
16
1
SO−16
D SUFFIX
CASE 751B
NCP1280
AWLYWW
1
NCP1280 = Device Code
A = Assembly Location
WL = Wafer Lot
Y = Year
WW = Work Week
PIN CONNECTIONS
1
Vin
NC
UV/OV
FF
CS
CSKIP
RT
DCMAX
16
VAUX
OUT1
GND
OUT2
tD
VREF
VEA
SS
ORDERING INFORMATION
Device
Package
Shipping†
NCP1280DR2
SO−16 2500/Tape & Reel
†For information on tape and reel specifications,
including part orientation and tape sizes, please
refer to our Tape and Reel Packaging Specifications
Brochure, BRD8011/D.
Lout
+
Vin
−
Start−up
(100 V − 425 V)
Cclamp
Feedforward
SR
Drive
Cout
+
Vout (3.3 V)
−
Vin FF
NCP1280
UV/OV
OUT1
OUT2
Overlap tD
Delay
Driver
Opto
Error
Amplifier
Figure 1. Forward Converter for Off−line Applications Using PFC Inputs
© Semiconductor Components Industries, LLC, 2004
April, 2004 − Rev. 1
1
Publication Order Number
NCP1280/D
1 page  
NCP1280
ELECTRICAL CHARACTERISTICS (Vin = 82 V, VAUX = 12 V, VEA = 2 V, RT = 101 kW, CCSKIP = 6800 pF,
RD = 60.4 kW, RFF = 1.0 MW, for typical values TJ = 25°C, for min/max values, TJ = −40°C to 125°C, unless otherwise noted)
Characteristic
Symbol
Min
Typ Max
START−UP CONTROL AND VAUX REGULATOR
VAUX Regulation
Start−up Threshold/VAUX Regulation Peak (VAUX increasing)
Minimum Operating VAUX Valley Voltage After Turn−On
Hysteresis
Minimum Start−up Voltage (Pin 1)
ISTART = 1.5 mA, VAUX = VAUX(on) − 0.2 V, IREF = 0 A
VAUX(on)
VAUX(off)
VH
VSTART(min)
10.5
6.6
−
−
11.0
7.0
4.0
−
11.5
7.4
−
25
Start−up Circuit Output Current
VAUX = 0 V
TJ = 25°C
TJ = −40°C to 125°C
VAUX = VAUX(on) − 0.2 V
TJ = 25°C
TJ = −40°C to 125°C
ISTART
13 17.5 21
10 − 25
10 13.8 17
8 − 19
Start−up Circuit Off−State Leakage Current (Vin = 700 V)
TJ = 25°C
TJ = −40°C to 125°C
ISTART(off)
−
−
23 50
− 100
Start−up Circuit Breakdown Voltage (Note 2)
ISTART(off) = 50 mA, TJ = 25°C
V(BR)DS
700
−
−
Auxiliary Supply Current After VAUX Turn−On
Outputs Disabled
VEA = 0 V
VUV/OV = 0.7 V
Outputs Enabled
LINE UNDER/OVERVOLTAGE DETECTOR
IAUX1 − 2.7 5.0
IAUX2 − 1.3 2.5
IAUX3 − 4.6 6.5
Undervoltage Threshold (Vin Increasing)
Undervoltage Hysteresis
Overvoltage Threshold (Vin Increasing)
Overvoltage Hysteresis
Undervoltage Propagation Delay to Output
Overvoltage Propagation Delay to Output
CURRENT LIMIT
VUV
VUV(H)
VOV
VOV(H)
tUV
tOV
1.40
0.080
3.47
−
−
−
1.52
0.098
3.61
0.145
250
160
1.64
0.120
3.75
−
−
−
Cycle by Cycle Threshold Voltage
Propagation Delay to Output (VEA = 2.0 V)
VCS = ILIM1 to 2.0 V, measured when VOUT reaches 0.5 VOH
ILIM1
tILIM
0.44 0.48 0.52
− 90 150
Cycle Skip Threshold Voltage
Cycle Skip Charge Current (VCSKIP = 0 V)
2. Guaranteed by design only.
ILIM2
ICSKIP
0.54
8.0
0.57 0.62
12.3 15
Unit
V
V
mA
mA
V
mA
V
V
V
V
ns
ns
V
ns
V
mA
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5
5 Page 
NCP1280
TYPICAL CHARACTERISTICS
80
Measured from 10% to 90% of VOH
70 VAUX = 12 V
60 TJ = 25°C
TJ = 125°C
50
40
30
20 TJ = −40°C
10
0
0 25 50 75 100 125 150 175 200
CL, LOAD CAPACITANCE (pF)
Figure 27. Outputs Rise Time versus Load
Capacitance
35
Measured from 90% to 10% of VOH
30 VAUX = 12 V
25 TJ = 125°C
20
TJ = 25°C
15
10 TJ = −40°C
5
0
0 25 50 75 100 125 150 175 200
CL, LOAD CAPACITANCE (pF)
Figure 28. Outputs Fall Time versus Load
Capacitance
DETAILED OPERATING DESCRIPTION
Introduction
An NCP1280 based system offers significant efficiency
improvements and system cost savings over a converter
using a traditional forward topology. The NCP1280
provides two control outputs. OUT1 controls the primary
switch of a forward converter. OUT2 has an adjustable
overlap delay, which can be used to control an active
clamp/reset switch or any other complementary drive
topology, such as an asymmetric half−bridge. In addition,
OUT2 can be used to control a synchronous rectifier
topology, eliminating the need of external control circuitry.
Other distinctive features include: two mode overcurrent
protection, line under/overvoltage detectors, fast line
feedforward, soft start and a maximum duty cycle limit. The
Functional Block Diagram is shown in Figure 2.
The features included in the NCP1280 provide some of
the advantages of Current−Mode Control, such as fast line
feedforward, and cycle by cycle current limit. It eliminates
the disadvantages of low power jitter, slope compensation
and noise susceptibility.
Active Clamp Topology
The transformer reset voltage in a traditional forward
converter is set by the turns ratio and input voltage. Where
as the reset voltage of an active clamp topology is constant
over the converter off time and only depends on the input
voltage and duty cycle. This translates into a lower voltage
stress on the main switch, allowing the use of lower voltage
MOSFETs. In general, lower voltage MOSFETs have lower
cost and ON resistance. Therefore, lower system cost and
higher efficiency can be achieved. In addition, the lower
voltage stress allows the converter to operate at a higher duty
cycle for a given primary switch voltage stress. This allows
a reduction in primary peak current and secondary side
voltage stress as well as smaller secondary inductor size.
High Voltage Start−up Regulator
The NCP1280 contains an internal 700 V start−up
regulator that eliminates the need for external start−up
components. In addition, this regulator increases the
efficiency of the supply as it uses no power when in the
normal mode of operation, but instead uses power supplied
by an auxiliary winding.
The start−up regulator consists of a constant current source
that supplies current from the input line voltage (Vin) to the
capacitor on the VAUX pin (CAUX). The start−up current is
typically 13.8 mA. Once VAUX reaches 11 V, the start−up
regulator turns OFF and the outputs are enabled. When VAUX
reaches 7 V, the outputs are disabled and the start−up
regulator turns ON. This “7−11” mode of operation is known
as Dynamic Self Supply (DSS). The VAUX pin can be biased
externally above 7 V once the outputs are enabled to prevent
the start−up regulator from turning ON. It is recommended
to bias the VAUX pin using an auxiliary supply generated by
an auxiliary winding from the power transformer. An
independent voltage supply can also be used. If using an
independent voltage supply and VAUX is biased before the
outputs are enabled or while a fault is present, the One Shot
Pulse Generator (Figure 2) will not be enabled and the
outputs will remain OFF.
As the DSS sources current to the VAUX pin, a diode should
be placed between CAUX and the auxiliary supply as shown
in Figure 29. This will allow the NCP1280 to charge CAUX
while preventing the start−up regulator from sourcing current
into the auxiliary supply.
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| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet NCP1280DR2.PDF ] | |
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