NCP1238 PDF даташит
Спецификация NCP1238 изготовлена «ON Semiconductor» и имеет функцию, называемую «Fixed Frequency Current Mode Controller». |
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Детали детали
Номер произв | NCP1238 |
Описание | Fixed Frequency Current Mode Controller |
Производители | ON Semiconductor |
логотип |
30 Pages
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NCP1238
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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 VCC 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).
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MARKING
DIAGRAM
SOIC−7
CASE 751U
8
38Xff
ALYWX
G
1
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
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 29 of this data sheet.
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)
• VCC 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.
© Semiconductor Components Industries, LLC, 2010
February, 2010 − Rev. 1
1
Publication Order Number:
NCP1238/D
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NCP1238
1 Latch
HV 8
2 FB
3 CS
VCC 6
4 GND
DRV 5
Figure 1. Pinout
TYPICAL APPLICATION EXAMPLE
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VIN
(dc)
LATCH
FB
CS
GND
NCP1238
HV
VCC
DRV
VOUT
Figure 2. Typical Application
PIN FUNCTION DESCRIPTION
Pin No
Pin Name
Function
1
LATCH
Latch−off Input
2 FB
Feedback
3 CS Current Sense
4 GND
–
5
DRV
Drive Output
6 VCC
VCC Input
8 HV High−Voltage Pin
Pin Description
Pull the pin up or down to latch−off the controller. An internal current source allows
the direct connection of an NTC for over temperature detection
A pull−down optocoupler controls the output regulation.
Senses the primary current for current−mode operation, and provides a mean for
overpower compensation adjustment.
IC ground
Drives an external MOSFET
This supply pin accepts up to 28 Vdc
Connects to the bulk capacitor or the rectified AC line to perform the functions of
Dynamic Self−Supply and brown−out / line overvoltage detections
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2
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VDD
INTC
INTC
NCP1238
SIMPLIFIED INTERNAL BLOCK SCHEMATIC
+
+−
VOVP
blanking
tLatch(OVP)
Brown−out
HV stop
HV sample
BO
OVM
HV dc
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HV
Latch
1 kW
Vclamp
VDD
RFB(up)
−
++
VOTP
FB
blanking
tLatch(OTP)
Soft−start
end
Brown−out
Reset
S
Q
R
−
++
V skip
TSD
Latch
Reset
UVLO
VDD
IC Start
TSD
Dual HV
start−up
current source
TSD HV current
RVUDeVsDLeOtmanaVgCeCment
Start
Soft−skip ramp
Reset
tSSKIP
Skip
FB
HV sample
V to I
IOPC = 0.5m x
(VHV−125)
VFB(OPC)
blanking
tLEB
CS
blanking
tBCS
KFB
+
−
slope
comp.
PWM
Soft−start
+
−
tSSTART
Soft−start
ramp
Start
End Reset
IC Start
IC Stop
Soft−start end
+
+
−
VILIM
Skip
Jitter
Sawtooth
Stop Foldback
Oscillator
DMAX
DCMAX
FB
Clamp
S
Q
R
ILIMIT
IC stop
ILIMIT
DMAX
S
Q
Fault Flag
R
PWM
UVLO
+
+−
VCS(stop)
tfaulttimer Fault
Brown−out
Reset
Protection
Mode
release
Autorecovery
protection
mode only
timer
tautorec
Figure 3. Simplified Internal Block Schematic
HV stop
Latch
TSD
VCC
DRV
GND
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3
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