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NCP1251

Current-Mode PWM Controller for Off-line Power Supplies

ON Semiconductor 

NCP1251

Current-Mode PWM

Controller for Off-line

Power Supplies

The NCP1251 is a highly integrated PWM controller capable of

delivering a rugged and high performance offline power supply in a

tiny TSOP−6 package. With a supply range up to 28 V, the controller

hosts a jittered 65 kHz or 100 kHz switching circuitry operated in peak

current mode control. When the power on the secondary side starts to

decrease, the controller automatically folds back its switching

frequency down to a minimum level of 26 kHz. As the power further

goes down, the part enters skip cycle while limiting the peak current.

Over Power Protection (OPP) is a difficult exercise especially when

no−load standby requirements drive the converter specifications. The

ON proprietary integrated OPP lets you harness the maximum

delivered power without affecting your standby performance simply

via two external resistors. A latched Over Voltage Protection (OVP) is

combined on the same pin. For ease of implementation, a latched OVP

also monitors the VCC line. They offer an efficient protection in case

of optocoupler destruction or adverse open loop operation.

Finally, a timer−based short−circuit protection offers the best

protection scheme, letting you precisely select the protection trip point

irrespective of a loose coupling between the auxiliary and the power

windings.

Features

• Fixed−Frequency 65 or 100 kHz Current−Mode Control Operation

• Internal and Adjustable Over Power Protection (OPP) Circuit

• Frequency Foldback Down to 26 kHz and Skip−Cycle in Light Load

Conditions

• Internal Ramp Compensation

• Internal Fixed 4 ms Soft−Start

• 100 ms Timer−Based Auto−Recovery Short−Circuit Protection

• Frequency Jittering in Normal and Frequency Foldback Modes

• Option for Auto−Recovery or Latched Short−Circuit Protection

• OVP Input for Improved Robustness

• Up to 28 V VCC Operation

• Latched OVP Protection on VCC

• +300 mA / −500 mA Source/Sink Drive Capability

• Less than 100 mW Standby Power at High Line

• EPS 2.0 Compliant

• These are Pb−Free Devices

Typical Applications

• ac−dc Converters for TVs, Set−top Boxes and Printers

• Offline Adapters for Notebooks and Netbooks

http://onsemi.com

MARKING

DIAGRAM

TSOP−6

(SOT23−6)

5AxAYWG

SN SUFFIX

G

1

CASE 318G

1

STYLE 13

5Ax = Specific Device Code

x

= A, 2, C, or D

A

= Assembly Location

Y

= Year

W

= Work Week

G

= Pb−Free Package

(Note: Microdot may be in either location)

PIN CONNECTIONS

GND 1

6 DRV

FB 2

OPP/Latch 3

5 VCC

4 CS

(Top View)

ORDERING INFORMATION

See detailed ordering and shipping information in the package

dimensions section on page 2 of this data sheet.

© Semiconductor Components Industries, LLC, 2011

1

October, 2011 − Rev. 7

Publication Order Number:

NCP1251/D

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