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NCP1234 Datasheet PDF : 33 Pages
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NCP1234
Fixed Frequency Current
Mode Controller for Flyback
Converters
The NCP1234 is a new fixed−frequency current−mode controller
featuring Dynamic Self−Supply (DSS). This device is pin−to−pin
http://onsemi.com
compatible with the previous NCP12xx families.
The DSS function greatly simplifies the design of the auxiliary
supply and the VCC capacitor by activating the internal startup current
source to supply the controller during transients.
Due to frequency foldback, the controller exhibits excellent
efficiency in light load condition while still achieving very low
SOIC−7
CASE 751U
standby power consumption. Internal frequency jittering, ramp
compensation, and a versatile latch input make this controller an
MARKING DIAGRAM
excellent candidate for converters where components cost is the key
8
constraints.
It features a timer−based fault detection that ensures the detection of
overload independently of an auxiliary winding, and an adjustable
compensation to help keep the maximum power independent of the
input voltage.
Finally, due to a careful design, the precision of critical parameters
is well controlled over the entire temperature range (−40C to
+125C).
Features
Fixed−Frequency Current−Mode Operation with Built−In Ramp
34Xff
ALYWX
G
1
34Xff = Specific Device Code
X = A or B
ff = 65 or 100
A = Assembly Location
L = Wafer Lot
Y = Year
W = Work Week
G = Pb−Free Package
Compensation
65 kHz or 100 kHz Oscillator Frequency version
Frequency Foldback then Skip Mode for Maximized Performance in
PIN CONNECTIONS
Latch 1
8 HV
Light Load and Standby Conditions
Timer−Based Overload Protection with Latched (option A) or
Auto−Recovery (option B) Operation
High−voltage Current Source with Dynamic Self−Supply,
Simplifying the Design of the VCC Capacitor
Frequency Modulation for Softened EMI Signature, including during
Frequency Foldback mode
Adjustable Overpower Compensation
Latch−off Input for Severe Fault Conditions, Allowing Direct
FB 2
CS 3
GND 4
6 VCC
5 DRV
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 32 of this data sheet.
Connection of an NTC for Overtemperature Protection (OTP)
VCC Operation up to 28 V, with Overvoltage Detection
500 mA Peak Source/Sink Current Drive Capability
4.0 ms Soft−Start
Internal Thermal Shutdown
Pin−to−Pin Compatible with the Existing NCP12xx
Series
Typical Applications
AC−DC Adapters for Notebooks, LCD, and Printers
Offline Battery Chargers
These Devices are Pb−Free, Halogen Free/BFR Free
Consumer Electronic Power Supplies
and are RoHS Compliant
Auxiliary/Housekeeping Power Supplies
Semiconductor Components Industries, LLC, 2011
1
October, 2011 − Rev. 1
Publication Order Number:
NCP1234/D
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