Fairchild (Now ON) SG6859ADZ, SG6859ATZ, SG6859ATZ, SG6859ADZ Schematics

March 2008

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 Start-up Current: 9μA  Low Operating Current: 3mA  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)

 Gate Output Voltage Clamped at 17V  Low Cost  Few External Components Required  Small SOT-26 Package

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 start-up current to 9μA and the operating current to 3mA. To further improve power conservation, a large start-up 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 SOT-26 packages.

to 264VAC). Pulse-by-pulse current

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

Ordering Information

Part Number Operating Temperature Range Package Packing Method

SG6859ATZ

SG6859ADZ

All packages are lead free per JEDEC: J-STD-020B standard.

-20°C to +85°C

SOT-26

DIP-8

Tape & reel

Tube

Application Diagram

Internal Block Diagram

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

Figure 1. Typical Application

Figure 2. Functional Block Diagram

Pin Configuration

SOT-26

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

DIP-8

GND

GATE

VDD

SENSE

GATE

VDD

SENSE

Figure 3. Pin Configurations

Pin Definitions

DIP

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.

SOT

Pin #

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 overcurrent 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 current I

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.

and a 70kHz switching frequency.

results in a 50μA constant

GND

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

Absolute Maximum Ratings

Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only.

Symbol Parameter Min. Max. Unit

DC Supply Voltage

VDD

VFB Input Voltage to FB Pin -0.3 7.0 V

Input Voltage to Sense Pin -0.3 7.0 V

SENSE

TJ Operating Junction Temperature 150

ΘJA

STG

Thermal Resistance (Junction-to-Air)

Storage Temperature Range -55 150

TL Lead Temperature (Wave Soldering or IR, 10 Seconds) 260

ESD

Electrostatic Discharge Capability, Human Body Model 3.5 kV

Electrostatic Discharge Capability, Machine Model 200 V

Notes:

1. All voltage values, except differential voltages, are given with respect to GND pin.

2. Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device.

(1, 2)

30 V

°C

SOT 208.4

DIP 82.5

°C/W

°C

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