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SG6846A

Highly Integrated Green-Mode PWM Controller

Fairchild Semiconductor 

September 2008

SG6846A

Highly Integrated Green-Mode PWM Controller

Features

ƒ Low Startup Current: 8µA

ƒ Low Operating Current: 3.7mA

ƒ Peak-Current Mode of Operation with Cycle-by-

Cycle Current Limiting

ƒ PWM Frequency Continuously Decreasing with

Burst Mode at Light Loads

ƒ VDD Over-Voltage Protection (OVP)

ƒ AC Input Brownout Protection with Hysteresis

ƒ Constant Output Power Limit (Full AC Input Range)

ƒ Internal Latch Circuit for OVP, OTP, and OCP

ƒ Two-level OCP Delay: 1600ms

ƒ Output Short-Circuited Delay Time: 100ms

ƒ Programmable PWM Frequency with

Frequency Hopping

ƒ OCP Threshold is Half Peak Current Limit

ƒ Feedback Open-loop Protection with 1700ms Delay

ƒ Built-in Soft-Start

Applications

General-purpose switch-mode power supplies and

flyback power converters, including:

ƒ Power Adapters

ƒ Open-frame SMPS

ƒ SMPS with Surge-current Output, such as for

Printers, Scanners, Motor Drivers

Description

The SG6846A is especially designed for SMPS with

surge-current output, incorporated with a two-level OCP

function. Besides the cycle-by-cycle current limiting, if

the switching current is higher than two thirds the peak-

current threshold for 1700ms, over-current protection is

activated such that the SG6846A is latched off.

If the switching current is higher than two thirds of the

peak-current threshold for 100ms, and the voltage on

the VDD is still higher than VDD-OFF + 1V, the PWM

pulses are latched off immediately once the VDD voltage

is lower than VDD-OFF + 1V. This is useful when an

output short circuit occurs.

SG6846A also integrates a frequency-hopping function

internally to reduce EMI emission of a power supply

with minimum line filters. Its built-in synchronized slope

compensation provides proprietary internal

compensation for constant output power limit over

universal AC input range. Also, the gate output is

clamped at 18V to protect the external MOSFET from

over-voltage damage. Internal soft-start is built-in to

soften the stress on the MOSFET and startup current

during power on period.

Other protection functions include AC input brownout

protection with hysteresis, VDD over-voltage protection,

and over-temperature protection. For over-temperature

protection, an external NTC thermistor can be applied to

sense the ambient temperature. When OCP, VDD OVP,

or OTP is activated, an internal latch circuit latches off

the controller. The PWM pulses stay latched off until the

power supply is disconnected from the mains outlet.

SG6846A controller is available in 8-pin SOP package.

Ordering Information

Part

Operating

OCP

Number Temperature Range Latch

SG6846ALSY

-40 to +105°C

Yes

SG6846ACSY

-40 to +105°C

No

SG6846ALSZ

-40 to +105°C

Yes

Eco

Status

Green

Green

RoHS

Package

Packing

Method

8-Pin Small Outline Package (SOP)

8-Pin Small Outline Package (SOP)

8-Pin Small Outline Package (SOP)

Tape & Reel

Tape & Reel

Tape & Reel

For Fairchild’s definition of “green” Eco Status, please visit: http://www.fairchildsemi.com/company/green/rohs_green.html.

© 2008 Fairchild Semiconductor Corporation

SG6846A • Rev. 1.1.4

www.fairchildsemi.com

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