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PDF NCP1212DR2 Data sheet ( Hoja de datos )
| Número de pieza | NCP1212DR2 | |
| Descripción | Current Mode PWM Controller for Both Forward and Flyback Converters | |
| Fabricantes | ON | |
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NCP1212
Current Mode PWM
Controller for Both Forward
and Flyback Converters
NCP1212 is a high performance current mode PWM controller
specifically designed for off−line and DC−to−DC converter
applications. The device requires very few external components and
offers designer additional protection for better system reliability. The
device features a trimmed oscillator for precise Duty Cycle control,
accurate bandgap voltage reference, high gain error amplifier, current
sensing comparator and a high current totem pole output gate driver
that ideally drives the external power MOSFET. Additionally, the
device has built−in programmable Brownout Detect and Soft−Start
features to enhance system reliability. Also, the 48%/82% selectable
maximum turn on Duty Cycle control and external programmable
switching frequency capabilities make this device an ideal controller
for both forward and flyback configurations. This device is available
in both PDIP−8 and space saving SOIC−8 packages.
Features
• Pb−Free Package is Available
• Trimmed Oscillator Charge and Discharge Current for Precise Duty
Cycle Control
• Internal High Accuracy Bandgap Voltage Reference
• Current Mode Operation up to 200 kHz
• Inherent Feed Forward Compensation
• Latching PWM for Cycle−by−Cycle Current Limiting
• High Current Totem Pole Output Gate Driver
• Low Startup and Operating Current
• Internal Undervoltage Lockout with Hysteresis
• Internal Leading Edge Blanking for Current Feedback
• Direct Interface with Optocoupler for Secondary Sensing
• Built−in Soft−Start Function, Programmable by External Capacitor
• User Programmable 48%/82% Maximum Duty Cycle Selection
• Output Overvoltage Protection Against Open Loop
• AC Line Brownout Detect Protection
• Output Overload Protection Irrespective of Auxiliary Voltage Level
Typical Applications
• ATX PC Power Supply
• Universal Input Wall Mount Adaptors
• CRT Monitor
• All Flyback and Forward SMPS Systems
http://onsemi.com
8
1
8
1
MARKING
DIAGRAMS
SOIC−8
D SUFFIX
CASE 751
8
N1212
ALYW
1
PDIP−8
P SUFFIX
CASE 626
8
1
NCP1212
AWL
YYWW
A = Assembly Location
WL, L = Wafer Lot
YY, Y = Year
WW, W = Work Week
PIN CONNECTIONS
FB 1
BOK 2
CS 3
CT 4
8 SS/DMAX
7 VCC
6 DRV
5 GND
(Top View)
ORDERING INFORMATION
Device
NCP1212DR2
NCP1212P
NCP1212PG
Package
SOIC−8
PDIP−8
PDIP−8
(Pb−Free)
Shipping†
2500 Tape & Reel
50 Units/Rail
50 Units/Rail
†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.
© Semiconductor Components Industries, LLC, 2004
October, 2004 − Rev. 2
1
Publication Order Number:
NCP1212/D
1 page  
NCP1212
ELECTRICAL CHARACTERISTICS (For typical values TJ = 25°C, DMAX = 48%, for min/max values TJ = −25°C to +105°C,
VCC = 16 V unless otherwise noted.)
Characteristic
Symbol
Min Typ Max Unit
OSCILLATOR SECTION
Oscillation Frequency, TJ = 25°C (DMAX = 48%, CT = 1.0 nF)
FOSC−48
81 90 99 kHz
Oscillation Frequency, TJ = 25°C (DMAX = 82%, CT = 1.0 nF)
FOSC−82
72 80 88 kHz
Frequency Change against Supply Voltage
(VCC = 13 V to 25 V, TJ = 25°C)
DFOSC−V
− 0.02 −
%
Frequency Change against Temperature
(VCC = 16 V, TJ = −25°C to 105°C)
DFOSC−T
− 5.0 −
%
CURRENT SENSE SECTION
Maximum Current Sense Input Threshold
Propagation Delay (Current Sense to Gate after LEB Blanking)
VCS
TPLH
0.96 1.0 1.16
− 150 200
V
ns
Leading Edge Blanking Time
TLEB
− 300 −
ns
SOFT−START SECTION
Soft−Start Charge Current
Overload Timing Discharge Current (Note 3)
ISS
ISD−ISS
5.0 8.0 11
15 20 26
mA
mA
48% Duty Cycle Selection Input Voltage Threshold
VD48
− 2.5 −
V
82% Duty Cycle Selection Input Voltage Threshold
GATE DRIVER SECTION
VD82
− 3.0 −
V
Gate Drive Sink Capability, VCC = 15 V, VDRV = 1.0 V
IOL
− 100 −
mA
Gate Drive Source Capability, VCC = 15 V, VDRV = 5.0 V (Note 4)
Gate Drive Voltage (From 1.0 V to 11 V) Rise Time (CL = 1.0 nF, TJ = 25°C)
IOH
− 300 −
mA
Tr − 25 50 ns
Gate Drive Voltage (From 11 V to 1.0 V) Fall Time (CL = 1.0 nF, TJ = 25°C)
Tf − 25 50 ns
IC POWER SUPPLY SECTION
VCC Startup Threshold Voltage
VCCTH
13.5 15 16.5
V
VCC Overvoltage Lockout Threshold
VCC Undervoltage Lockout Threshold
VCCOVLO
VCCUVLO
22.5 25 27.5
8.5 10 11.5
V
V
Power Supply Current, before Startup (VCC = 12 V)
IC1 − 0.15 0.26 mA
Power Supply Current, Operating
IC2 − 3.0 5.0 mA
Power Supply Current, Shutdown (VCC = 15 V)
IC3
− 3.0 −
mA
BROWNOUT DETECT SECTION (BOK)
Brownout Input Threshold Voltage
Brownout Hysteresis Current
VBOK
IBOK
1.14 1.21 1.27
38 45 54
V
mA
MAXIMUM DUTY CYCLE SECTION
Maximum Duty Cycle at Soft−Start Pin Voltage between 2.1 V and 2.8 V
(2.1 V v VDMAX v 2.8 V)
DMAX48
47 48 50
%
Maximum Duty Cycle at Soft−Start Pin Voltage Higher than 3.0 V
(VDMAX w 3.0 V)
3. ISD is an internal current source not accessible externally.
4. The output voltage is internally clamped by 13.5 V Zener.
DMAX82
79 82 88
%
http://onsemi.com
5
5 Page 
NCP1212
DETAILED OPERATING DESCRIPTIONS
INTRODUCTION
The NCP1212 implements a standard current mode
architecture where the switch−off time is dictated by the
peak current setpoint. This device represents an ideal
candidate where low external part−count is the key system
requirement. Additionally, the device provides extensive
value−added functions, Soft−Start, Brownout Detect, etc.,
that can be applied to low−cost AC−DC adaptor
applications. The NCP1212 incorporates all the necessary
functions normally needed in UC384X based power supply
systems: Oscillator section, PWM Latch section, Current
Sense section, Brownout Detect protection, Soft−Start and
Maximum Duty Cycle Selection. With all those functions,
this device becomes a good alternative to UC384X that can
help to improve both performance and system cost. Also, the
innovative Maximum Duty Cycle Selection feature allows
the device applied to both forward and fly−back mode
configurations. Detailed functions of individual internal
blocks are described in below and a simplified functional
block diagram is shown in Figure 2.
Oscillator Section
The oscillator frequency is programmed by the capacitor
connected to CT pin. The capacitor is charged by a constant
current source to 3.8 V and 2.5 V for 82% and 48%
maximum Duty Cycle condition respectively. Once the
selected voltage is reached, CT is then discharged by another
constant current source down to 1.0 V and this charging and
discharging action will carry on perpetually. Desirable
switching frequency can be selected by choosing proper
value of timing capacitor, CT. The CT pin waveform is
shown in Figure 32.
82%
48%
48%
3.8 V
2.5 V
1.0 V
Figure 32. CT Pin Waveform for Oscillator
PWM Latch Section
NCP1212 works in current mode. The power switch
current is converted to a positive voltage by inserting a
sensing resistor Rsense between the power switch source and
the ground. The power switch peak current is compared with
the level shifted control input voltage on a cycle−by−cycle
basis. Figure 27 illustrated the internal blocks of the
function. The PWM latch is initialized by the Oscillator set
signal and is terminated by the current sense comparator
when the current exceeds the value dictated by the control
input or current limit level. The current sense Comparator
Latch configuration used ensures that only a single pulse
appears at the output during any given oscillator cycle.
+5 V
9K
1 4 3R
2 FB
3
R
− PWM Control
Output
+
Rsense
CS
300 ns
LEB
Current
− Limit
Output
+
+ 1V
− Oscillator
Reset
Set
Totem Pole Driver
RQ
F/F
SQ
DRV
Figure 33. PWM Latch Function
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11
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet NCP1212DR2.PDF ] | |
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