System General SG6848DP1, SG6848T1 Schematic [ru]

Product Specification

Low-cost Green-Mode PWM Controller for Flyback Converters

SG6848x1

FEATURES

 Green-mode PWM Controller
 Low Start-up Current (5uA)
 Low Operating Current (3mA)
 Programmable PWM Frequency
 Peak-current-mode Operation
 Leading-edge Blanking
 Built-in Synchronized Slope Compensation
 Cycle-by-cycle Current Limiting
 Constant Output Power Limit
 Gate Output Voltage Clamped at 15V
 Small SOT-26 Package Available

APPLICATIONS

General-purpose switching mode power supplies and

flyback power converters, such as

 Battery chargers
 Power adapters
 Open-frame SMPS
 Replacements for linear transformers and RCC
 5V standby power for PC power supply.

DESCRIPTION

This highly integrated PWM controller provides

several special 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
continuously decrease PWM frequency under light-load
conditions. This green-mode function enables the power
supply to easily meet even the strictest power
conservation requirements.

The BiCMOS fabrication process enables reducing
the start-up current to 5uA, and the operating current to
3mA. As a result, 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 (90VAC to
264VAC). Cycle-by-cycle current limiting ensures safe
operation during short-circuits.

To protect the external power MOSFET from being
damaged by supply over voltage, the SG6848x1’s output
driver is clamped at 15V. The SG6848x1’s controllers can
be used to improve the performance and reduce the
production cost of power supplies. The SG6848x1 is the
best choice for replacing linear and RCC power supplies.
It is available in DIP-8 and SOT-26 packages.

TYPICAL APPLICATION

© System General Corp. - 1 - www.sg.com.tw
Version 1.3(IAO33.0002.B4) Jan. 27, 2006

Product Specification

1

N

N

y

Low-cost Green-Mode PWM Controller for Flyback Converters

MARKING DIAGRAMS PIN CONFIGURATION

XXXMW

1

XXX:AAH =SG6848T1
XXX:AAH =SG6848TZ1
M: Mask Version
W: Week code A~Z=W1~W26

A

~Z=W27~W52

:Lead free package

GND

FB

RI

SOT-26

2

3

GATE

6

VDD

5

4

SENSE

8

DIP-8

SG6848x1

SG6848DP1

MXXXXXXYYWWV

1

D: D = DIP
P : Z = Lead Free

Null = Regular Package

M: Mask Version
XXXXXX: Wafer Lot
YY: Year; WW: Week
V: Assembl

Location

GATE

VDD

SENSE

C

1

2

3

4

ORDERING INFORMATION

Part Number Package

SG6848T1 SOT-26

SG6848D1 DIP-8

SG6848TZ1 SOT-26 (Lead Free)

SG6848DZ1 DIP-8 (Lead Free)

PIN DESCRIPTIONS

Name

GATE 1 / (6) Driver Output The totem-pole output driver for driving the power MOSFET.

VDD 2 / (5) Supply Power supply.

NC 3 No connection.

SENSE 4 / (4) Analog Input

RI 5 / (3)

NC 6 No connection.

FB 7 / (2) Analog Input

GND 8 / (1) Supply Ground.

Pin No.

DIP-8 / (SOT-26)

Type Function

Current sense. This pin senses the voltage across a resistor for peak-current-mode

control. If the voltage reaches the internal threshold, PWM output is disabled. This

activates cycle-by-cycle current limiting.

A resistor connected from the RI pin to GND pin will generate a constant current source

Analog

Input/Output

for the controller. This current is used to determine PWM frequency. Increasing the

resistance will reduce PWM frequency. A 95kΩ resistor results in a 70kHz PWM

frequency.

Feedback. The FB pin accepts the output voltage regulation signal. It provides feedback

to the internal PWM comparator to adjust the duty cycle.

GND

8

FB

7

6

5

C

RI

© System General Corp. - 2 - www.sg.com.tw
Version 1.3(IAO33.0002.B4) Jan. 27, 2006

Product Specification

Low-cost Green-Mode PWM Controller for Flyback Converters

BLOCK DIAGRAM

SG6848x1

© System General Corp. - 3 - www.sg.com.tw
Version 1.3(IAO33.0002.B4) Jan. 27, 2006

Product Specification

Low-cost Green-Mode PWM Controller for Flyback Converters

SG6848x1

ABSOLUTE MAXIMUM RATINGS

Symbol Parameter Value Unit

VDD DC Supply Voltage 25 V

VFB Input Voltage to FB Pin -0.3 to 6 V V

V

Input Voltage to Sense Pin -0.3 to 6V V

SENSE

PD Power Dissipation 300 mW

RθJA Thermal Resistance (Junction to Air)

TJ Operating Junction Temperature -40 to +125 °C

T

Storage Temperature Range -55 to +150 °C

STG

TR Peak Reflow Temperature

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

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

SOT-26 208.4 °C/W
DIP-8 82.5 °C/W

Pb free 260(+5/-0)

Pb 230(+5/-0)

°C

RECOMMENDED OPERATING JUNCTION TEMPERATURE: -30°C ~ 105°C*

*For proper operation

ELECTRICAL CHARACTERISTICS (VDD=15V, TA = 25°C, unless noted)

VDD Section

Symbol Parameter Test Condition Min. Typ. Max. Unit

VOP Continuously Operating Voltage 20 V

V

Start-up Threshold Voltage 15.3 16.3 17.3 V

TH(ON)

V

Min. Operating Voltage 10.9 11.7 12.5 V

DD(MIN)

I

Start-up Current 5 30 uA

DD ST

I

DD OP

V

Over Voltage Protection 22 23.5 25 V

DD-OVP

Operating Supply Current GATE = 1nF 3 5 mA

Feedback Input Section

Symbol Parameter Test Condition Min. Typ. Max. Unit

ZFB Input Impedance 2 kΩ

IOZ Zero-duty-cycle Input Current 1.3 2.0 mA

VOP Open Loop Voltage 4.5 V

Oscillator Section

Symbol Parameter Test Condition Min. Typ. Max. Unit

F

PWM Frequency RI = 95kΩ 65 70 75 kHz

OSC

F

FDY Frequency Variation versus VDD Deviation VDD = 14 to 20V 2 %

FDT Frequency Variation versus Temp. Deviation TA = -30 to 105 ℃ 2 %

IN Green-mode Start Threshold FB Input Current 1 mA

IG Green-mode Min. Freq. FB Input Current 1.16 mA

SG Green-mode Modulation Slope RI = 95kΩ 300 Hz/uA

RI RI pin resistance 66.5 150 kΩ

Green-mode Min. Frequency RI = 95kΩ 15 kHz

OSC-GREEN

© System General Corp. - 4 - www.sg.com.tw
Version 1.3(IAO33.0002.B4) Jan. 27, 2006

Product Specification

Low-cost Green-Mode PWM Controller for Flyback Converters

SG6848x1

Current Sense Section

Symbol Parameter Test Condition Min. Typ. Max. Unit

ZCS Input Impedance 10 kΩ

TPD Delay to Output 100 nsec

V

Current Limit Flatten Threshold Voltage 0.96 V

TH,FLT

V

DC

Current Limit Valley Threshold Voltage 0.81 V

TH,VALLEY

Duty Cycle of SAW Limit 45 %

SAW

Gate Section

Symbol Parameter Test Condition Min. Typ. Max. Unit

DC

Maximum Duty Cycle 70 75 80 %

(MAX)

DC

Minimum Duty Cycle 0 %

(MIN)

BNK Leading-edge Blanking Time 200 nsec

VOL Output Voltage Low Sink current = 20mA 1.5 V

VOH Output Voltage High Source current = 20mA 8 V

TR Rising Time GATE = 1nF 250 nsec

TF Falling Time GATE = 1nF 80 nsec

V

Output Clamp Voltage VDD = 20V 15 17 V

CLAMP

© System General Corp. - 5 - www.sg.com.tw
Version 1.3(IAO33.0002.B4) Jan. 27, 2006