Fairchild SG6859A service manual

August 2010

SG6859A

Low-Cost, Green-Mode PWM Controller for Flyback Converters

SG6859A — Low Cost, Green-Mode PWM Controller for Flyback Converters

Features



Green-Mode PWM

 Supports the “Blue Angel” Standard
 Low Startup Current: 9μA
 Low Operating Current: 3mA
 300mA Driving Capability
 Leading-Edge Blanking
 Constant Output Power Limit
 Universal Input
 Built-in Synchronized Slope Compensation
 Current-Mode Operation
 Cycle-by-cycle Current Limiting
 Under-Voltage Lockout (UVLO)
 Programmable PWM Frequency with Frequency

Hopping

 V

Over-Voltage Protection (Auto Restart)

DD

 Gate Output Voltage Clamped at 17V
 Low Cost
 Few External Components Required
 Small SSOT-6 Package

Applications

General-purpose switching mode power supplies and
flyback power converters, such as:

 Battery chargers for cellular phones, cordless

phones, PDAs, digital cameras, and power tools

 Power adapters for ink jet printers, video game

consoles, and portable audio players

 Open-frame SMPS for TV/DVD standby and auxiliary

supplies, home appliances, and consumer electronics

 Replacements for linear transformers and RCC SMPS
 PC 5V standby power

Description

This highly integrated PWM controller provides several
enhancements designed to meet the low standby-power
needs of low-power SMPS. To minimize standby power
consumption, the proprietary green-mode function
provides off-time modulation to linearly decrease the
switching frequency under light-load conditions. This
green-mode function enables the power supply to meet
even the strictest power conservation requirements.

The BiCMOS fabrication process enables reducing the
startup current to 9μA and the operating current to 3mA.
To further improve power conservation, a large startup
resistance can be used. Built-in synchronized slope
compensation ensures the stability of peak current
mode control. Proprietary internal compensation
provides a constant output power limit over a universal
AC input range (90V
limiting ensures safe operation during short-circuits.

To protect the external power MOSFET from damage by
supply over voltage, the SG6859A’s output driver is
clamped at 17V. SG6859A controllers can be used to
improve the performance and reduce the production
cost of power supplies. The best choice for replacing
linear and RCC-mode power adapters, the SG6859A is
available in 8-pin DIP and 6-pin SSOT-6 packages.

to 264VAC). Pulse-by-pulse current

AC

© 2007 Fairchild Semiconductor Corporation www.fairchildsemi.com
SG6859A • Rev. 1.0.4

Ordering Information

Part Number Operating Temperature Range Package Packing Method

SG6859ATZ

SG6859ATY

SG6859ADZ

SG6859ADY (Preliminary)

-40 to +105°C

-40 to +105°C

-40 to +105°C

-40 to +105°C

SSOT-6 Tape & Reel

SSOT-6 Tape & Reel

DIP-8 Tube

DIP-8 Tube

Application Diagram

SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters

Internal Block Diagram

Figure 1. Typical Application

Figure 2. Functional Block Diagram

© 2007 Fairchild Semiconductor Corporation www.fairchildsemi.com
SG6859A • Rev. 1.0.4 2

Marking Information

*Marking for SG6859ATZ (Pb-free)

AAJFW

AAJF: SG6859A
W

: Week Code
A~Z=W1~W26
A

~Z=W27~W52

: Lead Free Package

XXXX: AAJF=SG6859A

T : Die Run Code

. . . . : Year Code

---: Week Code

SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters

*Marking for SG6859ATY (Green Compound)

T: D=DIP
P: Z= Lead Free + RoHS Compatible

Null=Regular Package
XXXXXXXX: Wafer Lot
Y: Year
WW: Week
V: Assembly Location

*Marking for SG6859ADZ (Pb-free)

F- Fairchild Logo

Z- Plant Code
X- 1-Digit Year Code
Y- 1-Digit Week Code
TT: 2-Digit Die Run Code
T: Package Type (D=DIP)
P: Y: Green Package
M: Manufacture Flow Code

*Marking for SG6859ADY (Green Compound)

Figure 3. Top Mark

© 2007 Fairchild Semiconductor Corporation www.fairchildsemi.com
SG6859A • Rev. 1.0.4 3

Pin Configurations

SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters

Figure 4. SSOT-6 Pin Configuration Figure 5. DIP-8 Pin Configuration

Pin Definitions

DIP

Pin #

SSOT

Pin #

1 6 GATE The totem-pole output driver for driving the power MOSFET.

2 5 VDD Power supply

3 NC No connection

4 4 SENSE

5 3 RI

6 NC No connection

7 2 FB

8 1 GND Ground

Name Description

Current sense. This pin senses the voltage across a resistor. When the voltage
reaches the internal threshold, PWM output is disabled. This activates over-current
protection. This pin also provides current amplitude information for current-mode
control.

A resistor connected from the RI pin to ground generates a constant current source
used to charge an internal capacitor and determine the switching frequency.
Increasing the resistance reduces the amplitude of the current source and the
switching frequency. A 95kΩ resistor R
70kHz switching frequency.

Feedback. The FB pin provides the output voltage regulation signal. It provides
feedback to the internal PWM comparator, so that the PWM comparator can control
the duty cycle.

results in a 50μA constant current II and a

I

© 2007 Fairchild Semiconductor Corporation www.fairchildsemi.com
SG6859A • Rev. 1.0.4 4