© Semiconductor Components Industries, LLC, 2011
July, 2011 − Rev. 3
1 Publication Order Number:
NCP1238/D
NCP1238
Fixed Frequency Current
Mode Controller for Flyback
Converters
The NCP1238 is a new generation of the NCP12xx fixed−frequency
current−mode controllers featuring Dynamic Self−Supply (DSS),
pin−to−pin compatible with the previous generation.
The DSS function greatly simplifies the design of the auxiliary supply
and the V
CC
capacitor by activating the internal startup current source to
supply the controller during transients.
Due to its proprietary Soft−Skip™ mode combined with frequency
foldback, the controller exhibits excellent efficiency in light load
condition while still achieving very low standby power consumption.
This Soft−Skip feature also dramatically reduces the risk of acoustic
noise, which enables the use of inexpensive transformers and
capacitors in the clamping network.
Internal frequency jittering, ramp compensation, and a versatile
latch input make this controller an excellent candidate for converters
where ruggedness and components cost are the key constraints.
In addition, the controller includes a new high voltage circuitry that
combines a startup current source and a brown−out / line OVP detector
able to sense the input voltage either from the rectified ac line or the dc
filtered bulk voltage.
Finally, due to a careful design, the precision of critical parameters
is well controlled over the entire temperature range (−40°C to
+125°C), enabling easier design and increased safety (e.g. ±5% for the
peak current limit, ±7% for the oscillator).
Features
• Timer−Based Overload Protections with Auto−
Recovery (Option B) or Latched (Option A) Operation
• High−Voltage Current Source with DSS with Built−in
Brown−out and Line Overvoltage Protections
• Fixed−Frequency Current−Mode Operation with
Built−in Ramp Compensation
• Frequency Jittering for a Reduced EMI Signature
• Adjustable Overpower Compensation
• Latch−off Input for Severe Fault Conditions, with
Direct Connection of an NTC for Overtemperature
Protection (OTP)
• Protection Against Winding Short−Circuit
• Frequency Foldback transitioning into Soft−Skip for
Improved Performance in Standby
• 65 kHz Oscillator (100 kHz and 133 kHz Versions
Available Upon Request)
• V
CC
Operation up to 28 V
• Increased Precision on Critical Parameters
• ±1.0 A Peak Drive Capability
• 4.0 ms Soft−Start
• Internal Thermal Shutdown with Hysteresis
• These Devices are Pb−Free, Halogen Free/BFR Free
and are RoHS Compliant*
Typical Applications
• ac−dc Adapters for Notebooks, LCD, and Printers
• Offline Battery Chargers
• Consumer Electronic Power Supplies
• Auxiliary/Housekeeping Power Supplies
*For additional information on our Pb−Free strategy and soldering details, please
download the ON Semiconductor Soldering and Mounting Techniques
Reference Manual, SOLDERRM/D.
SOIC−7
CASE 751U
MARKING
DIAGRAM
http://onsemi.com
38Xff
ALYWX
G
1
8
38Xff = Specific Device Code
X = A or B
ff = 65, 00, or 33
A = Assembly Location
L = Wafer Lot
Y = Year
W = Work Week
G = Pb−Free Package
See detailed ordering and shipping information in the package
dimensions section on page 37 of this data sheet.
ORDERING INFORMATION
