© Semiconductor Components Industries, LLC, 2016
January, 2016 − Rev. 2
1 Publication Order Number:
NCP1234/D
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
compatible with the previous NCP12xx families.
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 frequency foldback, the controller exhibits excellent
efficiency in light load condition while still achieving very low
standby power consumption. Internal frequency jittering, ramp
compensation, and a versatile latch input make this controller an
excellent candidate for converters where components cost is the key
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 (−40°C to
+125°C).
Features
• Fixed−Frequency Current−Mode Operation with Built−In Ramp
Compensation
• 65 kHz or 100 kHz Oscillator Frequency version
• Frequency Foldback then Skip Mode for Maximized Performance in
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 V
CC
Capacitor
• Frequency Modulation for Softened EMI Signature, including during
Frequency Foldback mode
• Adjustable Overpower Compensation
• Latch−off Input for Severe Fault Conditions, Allowing Direct
Connection of an NTC for Overtemperature Protection (OTP)
• V
CC
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
• 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
SOIC−7
CASE 751U
MARKING DIAGRAM
www.onsemi.com
34Xff
ALYWX
G
1
8
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
See detailed ordering and shipping information in the package
dimensions section on page 32 of this data sheet.
ORDERING INFORMATION
18
5
3
4
(Top View)
Latch
CS
HV
PIN CONNECTIONS
6
2
FB
GND
DRV
V
CC
