NCP1351DPG Datasheet, PDF (1/27 Pages) ON Semiconductor – Variable Off Time PWM Controller

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.
8
1
http://onsemi.com
MARKING DIAGRAMS
SOIC-8
D SUFFIX
CASE 751
8
1351x
ALYW
G
1
8
1
PDIP-8
P SUFFIX
CASE 626
NCP1351x
AWL
YYWWG
1
x
= A, B, C, or D Options
A
= Assembly Location
L, WL = Wafer Lot
Y, YY = Year
W, WW = Work Week
G or G = Pb-Free Package
(Note: Microdot may be in either location)
PIN CONNECTIONS
FB 1
Ct 2
8 TIMER
7 LATCH
Features
•ăQuasi-fixed T_ON, Variable T_OFF Current Mode Control
•ăExtremely Low Current Consumption at Startup
•ăPeak Current Compression Reduces Transformer Noise
•ăPrimary or Secondary Side Regulation
•ăDedicated Latch Input for OTP, OVP
•ăProgrammable Current Sense Resistor Peak Voltage
•ăNatural Frequency Dithering for Improved EMI Signature
•ăEasy External Over Power Protection (OPP)
•ăUndervoltage Lockout
•ăVery Low Standby Power via Off-time Expansion
•ăSOIC-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
CS 3
GND 4
6 V_CC
5 DRV
(Top View)
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
©Ă Semiconductor Components Industries, LLC, 2007
1
November, 2007 - Rev. 3
Publication Order Number:
NCP1351/D