NCP1351
Variable Off Time PWM
Controller
The NCP1351 is a current-mode controller targeting low power
off-line flyback Switched Mode Power Supplies (SMPS) where cost
is of utmost importance. Based on a fixed peak current technique
(quasi-fixed T
ON
), the controller decreases its switching frequency as
the load becomes lighter. As a result, a power supply using the
NCP1351 naturally offers excellent no-load power consumption,
while optimizing the efficiency in other loading conditions. When the
frequency decreases, the peak current is gradually reduced down to
approximately 30% of the maximum peak current to prevent
transformer mechanical resonance. The risk of acoustic noise is thus
greatly diminished while keeping good standby power performance.
An externally adjustable timer permanently monitors the feedback
activity and protects the supply in presence of a short-circuit or an
overload. Once the timer elapses, NCP1351 stops switching and stays
latched for version A, and tries to restart for version B.
Versions C and D include a dual overcurrent protection trip point,
allowing the implementation of the controller in peak-power
requirements applications such as printers and so on. When the fault is
acknowledged, C version latches-off whereas D version
auto-recovers.
The internal structure features an optimized arrangement which
allows one of the lowest available startup current, a fundamental
parameter when designing low standby power supplies.
The negative current sensing technique minimizes the impact of the
switching noise on the controller operation and offers the user to select
the maximum peak voltage across his current sense resistor. Its power
dissipation can thus be application optimized.
Finally, the bulk input ripple ensures a natural frequency smearing
which smooths the EMI signature.
Features
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MARKING DIAGRAMS
8
8
1
SOIC-8
D SUFFIX
CASE 751
1
1351x
ALYW
G
8
1
PDIP-8
P SUFFIX
CASE 626
1
x
A
L, WL
Y, YY
W, WW
G
or G
NCP1351x
AWL
YYWWG
= A, B, C, or D Options
= Assembly Location
= Wafer Lot
= Year
= Work Week
= Pb-Free Package
(Note: Microdot may be in either location)
PIN CONNECTIONS
FB 1
Ct 2
CS 3
GND 4
(Top View)
8 TIMER
7 LATCH
6 V
CC
5 DRV
•
•
•
•
•
•
•
•
•
•
•
•
Quasi-fixed T
ON
, Variable T
OFF
Current Mode Control
Extremely Low Current Consumption at Startup
Peak Current Compression Reduces Transformer Noise
Primary or Secondary Side Regulation
Dedicated Latch Input for OTP, OVP
Programmable Current Sense Resistor Peak Voltage
Natural Frequency Dithering for Improved EMI Signature
Easy External Over Power Protection (OPP)
Undervoltage Lockout
Very Low Standby Power via Off-time Expansion
SOIC-8 Package
Standard Overcurrent Protection, Latched or
Auto-Recovery, A & B Versions
•
Dual Trip Point Overcurrent Protection, Latched or
Auto-Recovery, C & D Versions
•
These are Pb-Free Devices
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 25 of this data sheet.
Typical Applications
•
Auxiliary Power Supply
•
Printer, Game Stations, Low-Cost Adapters
•
Off-line Battery Charger
©
Semiconductor Components Industries, LLC, 2007
1
November, 2007 - Rev. 3
Publication Order Number:
NCP1351/D
NCP1351
+
V
OUT
NCP1351
+
85-265VAC
*OPP
1
2
3
4
8
7
6
5
LATCH
+
GND
*Optional
Figure 1. Typical Application Circuit
PIN FUNCTION DESCRIPTION
Pin N°
1
2
3
4
5
6
7
8
Pin Name
FB
Ct
CS
GND
DRV
V
CC
Latch
Timer
Function
Feedback Input
Oscillator Frequency
Current Sense Input
–
Driver Output
Supply Input
Latchoff Input
Fault Timer Capacitor
Pin Description
Injecting Current in this Pin Reduces Frequency
A capacitor sets the maximum switching frequency at no feedback current
Senses the Primary Current
–
Driving Pulses to the Power MOSFET
Supplies the controller up to 28 V
A positive voltage above V
LATCH
fully latches off the controller
Sets the time duration before fault validation
OVERCURRENT PROTECTION ON NCP1351 VERSIONS:
NCP1351
A
B
C
D
x
x
x
x
x
Auto-recovery
Latched
x
Dual level
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2
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