Product Specification

SG6848

Low Cost Green-Mode PWM Controller for Flyback Converters

FEATURES

DESCRIPTION

Green-Mode PWM
Supports the “Blue Angel” Standard
Low Start-up Current (5uA)
Low Operating Current (2mA)
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
Gate Output Voltage Clamped at 15V
Low Cost
Few External Components Required
Small SOT-26 Package

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 linearly
decrease the switching 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
2mA. 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 (90VAC to 264VAC). Pulse-by-pulse current
limiting ensures safe operation even during short-circuits.

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 other
auxiliary supplies, home appliances, and consumer
electronics
Replacements for linear transformers and RCC
SMPS
PC 5V standby power.

TYPICAL APPLICATION

To protect the external power MOSFET from being
damaged by supply over voltage, the SG6848’s output
driver is clamped at 15V. SG6848 controllers can be used
to improve the performance and reduce the production
cost of power supplies. The SG6848 is the best choice for
replacing linear and RCC-mode power adapters. It is
available in 8-pin DIP and 6-pin SOT-26 packages.

From bridge rectifier
120~ 380VDC
From auxiliary winding
RIN
1.5M
VDD

CIN
10u
R7
100

FB
OUTPUT

C6
472p

SG6848
R9
95k

SENSE

RI

RS
4.7

GND

© System General Corp.
Version 1.2(IRO33.0010.B0)

-1-

www.sg.com.tw
May.06, 2003

Product Specification

SG6848

Low Cost Green-Mode PWM Controller for Flyback Converters

MARKING DIAGRAMS

PIN CONFIGURATION

SOT-26
M: Mask Version
Y: Year; WW: Work Week

MAYWW

GND

1

6

GATE

FB

2

5

VDD

RI

3

4

SENSE

1
8

DIP-8
XXXXXXX: Wafer Lot
YY: Year; WW: Week
V: Assembly Location

SG6848D

XXXXXXXYYWWV

1

GATE

1

8

GND

VDD

2

7

FB

NC

3

6

NC

SENSE

4

5

RI

ORDERING INFORMATION
Part Number

PWM Frequency

Package

SG6848T

70kHz

6-Pin SOT-26

SG6848D

70kHz

8-pin DIP-8

PIN DESCRIPTIONS
Name

Pin No.
DIP-8 / (SOT-26)

Type

Function
The totem-pole output driver for driving the power MOSFET.

GATE

1 / (6)

Driver Output

VDD

2 / (5)

Supply

NC

3

SENSE

4 / (4)

Power supply.
NC pin.
Current sense. This pin senses the voltage across a resistor. When the voltage reaches

Analog Input

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 will generate a constant current source for

RI

5 / (3)

Analog
Input/Output

the SG6848. This current is used to charge an internal capacitor, to determine the
switching frequency. Increasing the resistance will reduce the amplitude of the current
source and reduce the switching frequency. A 95kΩ resistor Ri results in a 50uA constant
current Ii and a 70kHz switching frequency.

NC

6

NC pin.

FB

7 / (2)

Analog Input

GND

8 / (1)

Supply

© System General Corp.
Version 1.2(IRO33.0010.B0)

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.
Ground.

-2-

www.sg.com.tw
May.06, 2003

Product Specification

SG6848

Low Cost Green-Mode PWM Controller for Flyback Converters

BLOCK DIAGRAM
GND

RI

8 (1)

5 (3)

VDD
ON/OFF
Driver

Internal
Bias

VDD

2 (5)

OSC

GATE

4 (4)

SENSE

7 (2)

FB

S Q
R

OCP
Comp
Vlimit
ramp

+
_

1 (6)

Blanking
Circuit

Slope
Compensation

UVLO

4.8V

PWM
Comp

16.3V/11.7V
Green
Mode
Controller

ABSOLUTE MAXIMUM RATINGS
Symbol

Parameter

Value

Unit

VDD

DC Supply Voltage *

25

V

Zener Clamp

26

V

Zener Current

10

mA

VFB

Input Voltage to FB Pin

-0.3 to 6 V

V

VSense

Input Voltage to Sense Pin

-0.3 to 6V

V

Pd

Power Dissipation

300

mW

TJ

Operating Junction Temperature

150

℃

RθJA

Thermal Resistance (Junction to Air)

SOT-26

208.4

°C/W

DIP-8

82.5

°C/W

Tstg

Storage Temperature Range

-55 to +150

℃

TL

Lead Temperature (Soldering)

20 sec

SOT-26

220

10 sec

DIP-8

260

°C

ESD Capability, HBM Model

3.0

kV

ESD Capability, Model

300

V

* All voltage values, except differential voltages, are given with respect to the network ground terminal.

© System General Corp.
Version 1.2(IRO33.0010.B0)

-3-

www.sg.com.tw
May.06, 2003

Product Specification

SG6848

Low Cost Green-Mode PWM Controller for Flyback Converters

RECOMMENDED OPERATING CONDITIONS
Symbol

Parameter

Value

Unit

VDD

DC Supply Voltage

≦20

V

Ta

Operating Ambient Temperature

-30 to +85

℃

ELECTRICAL CHARACTERISTICS (TA = 25°°C, VDD=15V)
Feedback Input Section
Symbol

Parameter

Typ.

Max.

Unit

Ioz

Zero Duty Cycle Input Current

Test Condition

Min.

1.3

2.0

mA

Vop

Open Loop Voltage

4.5

V

Current Sense Section
Symbol

Parameter

Zcs

Input Impedance

Test Condition

Min.

Typ.

TPD

Delay to Output

150

VTH,FLT

Current Limit Flatten Threshold Voltage

1.0

VTH,VALLEY

Current Limit Valley Threshold Voltage

Max.

10

0.80

Unit
kΩ

0.85

200

nsec
V

0.90

V

Oscillator Section
Symbol

Parameter

Test Condition

Min.

Typ.

Max.

Unit

Fosc

Frequency

RI=95kΩ

65

70

75

kHz

Fosc-green

Green-Mode Frequency

RI=95kΩ

13

15

kHz

Ig

Green-Mode FB Input Current

In

Green-Mode Start Threshold FB Input Current
In = 0.3mA for a Maximum Duty Cycle

1.16

mA

1

mA

Sg

Green-Mode Modulation Slope

RI=95kΩ

300

Fdv

Frequency Variation versus VDD Deviation

VDD=12 to 20V

0.02

Fdt

Frequency Variation versus Temp. Deviation

TA=-30 to 85 ℃

Hz/uA
2

%

2

%

PWM Section
Symbol

Parameter

DC (MAX)
DC (MIN)
Bnk

Leading-Edge Blanking Time

Test Condition

Min.

Typ.

Max.

Unit

Maximum Duty Cycle

70

75

80

%

Minimum Duty Cycle

-

1

2

%

250

nsec

Output Section
Symbol

Parameter

Test Condition

Vol

Output Voltage Low

VDD=15V, Io=20mA

Voh

Output Voltage High

VDD=15V, Io=20mA

tr

Rising Time

VDD=15V, CL=1nF

tf

Falling Time

VCLAMP

Output Clamp Voltage

© System General Corp.
Version 1.2(IRO33.0010.B0)

Max.

Unit

1.5

V

50

200

nsec

VDD=15V, CL=1nF

30

150

nsec

VDD=20V

15

17

V

-4-

Min.

Typ.

8

V

www.sg.com.tw
May.06, 2003

Product Specification

SG6848

Low Cost Green-Mode PWM Controller for Flyback Converters

Under Voltage Lockout Section
Symbol

Parameter

Test Condition

Min.

Typ.

Max.

Unit

VTH(ON)

Start Threshold Voltage

TA=25°C

15.3

16.3

17.3

V

VDD(min)

Min. Operating Voltage

TA=25°C

10.9

11.7

12.5

V

Min.

Total Standby Current Section
Symbol

Parameter

Test Condition

Typ.

Max.

Unit

IDD ST

Start-up Current

VDD=15V

5

30

uA

IDD OP

Operating Supply Current

VDD=15V

2

5

mA

© System General Corp.
Version 1.2(IRO33.0010.B0)

-5-

www.sg.com.tw
May.06, 2003

Product Specification

SG6848

Low Cost Green-Mode PWM Controller for Flyback Converters

TYPICAL CHARACTERISTICS
Min. Operating Voltage (V DD (min)) vs
Temperature

Start-up Threshold Voltage (V TH(ON)) vs
Tem perature
12.2

17.0

12.0
11.8

VDD (min) (V)

VTH(ON) (V)

16.5

16.0

15.5

11.6
11.4
11.2
11.0

15.0

10.8
14.5

10.6
-40

-25

-10

5

20

35

50

65

80

95

110

125

-40

-25

-10

5

TEMPERATURE (℃
℃)

20

35

50

65

80

95

110

125

TEMPERATURE ( ℃ )

PWM Oscillator Frequency (FOSC) vs
Tem perature

Start-up Crrent (IDD ST) vs Tem perature
30
74.0

25

72.5

FOSC (KHz)

IDD ST (uA)

20
15
10

71.0
69.5
68.0

5

66.5

0

65.0
-40

-25

-10

5

20

35

50

65

80

95

110

125

-40

-25

-10

5

TEMPERATURE ( ℃ )

Frequency in green m ode (FOSC-green)
vs Tem perature

35

50

65

80

95

110

125

Max. Duty Cycle (DC(MAX)) vs
Tem perature
80

15

79

14

78

13

DC (MAX) (%)

FOSC-green (KHz)

20

TEMPERATURE (℃
℃)

12
11

77
76
75
74
73

10

72
9

71
70

8
-40

-25

-10

5

20

35

50

65

80

95

110

-40

125

TEMPERATURE ( ℃ )

© System General Corp.
Version 1.2(IRO33.0010.B0)

-25

-10

5

20

35

50

65

80

95

110

125

TEMPERATURE ( ℃ )

-6-

www.sg.com.tw
May.06, 2003

Product Specification
Low Cost Green-Mode PWM Controller for Flyback Converters

SG6848

PWM Oscillator Frequency (FOSC) vs.
FB
80
70

F OSC (KHz)

60
50
40
30
20
10
0
0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

FB (mA)

© System General Corp.
Version 1.2(IRO33.0010.B0)

-7-

www.sg.com.tw
May.06, 2003

Product Specification

SG6848

Low Cost Green-Mode PWM Controller for Flyback Converters

OPERATION DESCRIPTION
SG6848 devices integrate many useful designs into
one controller for low-power switch-mode power supplies.
The following descriptions highlight some of the features
of the SG6848 series.

switching frequency. Increasing the resistance will reduce
the amplitude of the input current and reduce the
switching frequency. A 95kΩ resistor Ri results in a 50uA
constant current Ii and a 70kHz switching frequency. The
relationship between Ri and the switching frequency is:

fPWM =

Start-up Current
The start-up current is only 5uA. Low start-up
current allows a start-up resistor with a high resistance
and a low-wattage to supply the start-up power for the
controller. A 1.5 MΩ, 0.25W, start-up resistor and a
10uF/25V VDD hold-up capacitor would be sufficient for
an AC-to-DC power adapter with a wide input range
(100VAC to 240VAC).

Operating Current
The operating current has been reduced to 2mA. The
low operating current results in higher efficiency and
reduces the Vcc hold-up capacitance requirement.

6650
R I (k Ω )

(kHz )

The range of the oscillation frequency is designed to
be within 50kHz ~ 100kHz.

Leading-Edge Blanking
Each time the power MOSFET is switched on, a
turn-on spike will inevitably occur at the sense-resistor.
To avoid premature termination of the switching pulse, a
250 nsec leading-edge blanking time is built in.
Conventional RC filtering can therefore be omitted.
During this blanking period, the current-limit comparator
is disabled and it cannot switch off the gate driver.

Constant Output Power Limit
Green-Mode Operation
The proprietary green-mode function provides
off-time modulation to linearly decrease the switching
frequency under light-load conditions. On-time is limited
to provide stronger protection against brownouts and
other abnormal conditions. The feedback current, which is
sampled from the voltage feedback loop, is taken as the
reference. Once the feedback current exceeds the
threshold current, the switching frequency starts to
decrease. This green-mode function dramatically reduces
power consumption under light-load and zero-load
conditions. Power supplies using the SG6848 can easily
meet even the strictest regulations regarding standby
power consumption.

Oscillator Operation
A resistor connected from the RI pin to ground will
generate a constant current source for the SG6848. This
current is used to charge an internal capacitor. The
charge-time determines the internal clock speed and the
© System General Corp.
Version 1.2(IRO33.0010.B0)

When the SENSE voltage across the sense resistor Rs
reaches the threshold voltage (around 1.0V), the output
GATE drive will be turned off following a short
propagation delay tD. This propagation delay will
introduce an additional current proportional to tD*Vin/Lp.
The propagation delay is nearly constant regardless of the
input line voltage VIN. Higher input line voltages will
result in larger additional currents. At high input line
voltages, the output power limit will be higher than at low
input line voltages.
To compensate for this output power limit variation
across a wide AC input range, the threshold voltage is
adjusted by adding a positive ramp. This ramp signal rises
from 0.85V to 1.0V, and then flattens out at 1.0V. A
smaller threshold voltage forces the output GATE drive to
terminate earlier. This reduces the total PWM turn-on
time and makes the output power equal to that of low line
input. This proprietary internal compensation ensures a
constant output power limit for a wide AC input voltage
range (90VAC to 264VAC).

-8-

www.sg.com.tw
May.06, 2003

Product Specification
Low Cost Green-Mode PWM Controller for Flyback Converters

SG6848

Under Voltage Lockout (UVLO)
The turn-on and turn-off thresholds of the SG6848
are fixed internally at 16.3V/11.7V. During start-up, the
hold-up capacitor must be charged to 16.3V through the
start-up resistor, so that the SG6848 will be enabled. The
hold-up capacitor will continue to supply VDD until power
can be delivered from the auxiliary winding of the main
transformer. VDD must not drop below 11.7V during this
start-up process. This UVLO hysteresis window ensures
that hold-up capacitor will be adequate to supply VDD
during start-up.

Built-in Slope Compensation
The sensed voltage across the current sense resistor
is used for current mode control and pulse-by-pulse
current limiting. Built-in slope compensation will
improve stability and prevent sub-harmonic oscillations
due to peak-current mode control. The SG6848 has a
synchronized, positively-sloped ramp built-in at each
switching cycle. The slope of the ramp is:

0.33 × Duty
Duty(max)

Gate Output
The SG6848 BiCMOS output stage is a fast totem
pole gate driver. Cross conduction has been avoided to
minimize heat dissipation, increase efficiency, and
enhance reliability. The output driver is clamped by an
internal 15V Zener diode in order to protect power
MOSFET transistors against undesired over-voltage gate
signals.

© System General Corp.
Version 1.2(IRO33.0010.B0)

Noise Immunity
Noise from the current sense or the control signal can
cause significant pulse width jitter, particularly in
continuous-conduction mode. While slope compensation
helps alleviate these problems, further precautions should
still be taken. Good placement and layout practices should
be followed. Avoiding long PCB traces and component
leads, locating compensation and filter components near
the SG6848, and increasing the power MOS gate
resistance is advised.

-9-

www.sg.com.tw
May.06, 2003

Product Specification

SG6848

Low Cost Green-Mode PWM Controller for Flyback Converters

REFERENCE CIRCUIT
Circuit
F1

L1

1

CX1

2

BD1

2 -

+ 4

+

C1

R1
C2

C3

R3

R5

R4

D4

T1

3

N

R2

3

1

L2

1

VO

2

GATE

FB

VDD

RI

SENSE

6

C7
C8

+

D5

Q1

1

+

C9

2

GND

R7

R10

8
5

5

3

2

C6

2

9

D1
22

U1
1

1,2

1

10

1

1

L

7

4

GND

3,4

R6

R9
R8
+

1

D2

2

R11

C4
U2
4

R13

1
2

C10

3

3

R14

U3

CY1

1

2

R12

BOM
Reference

Component

Reference

Component

BD1

BD 1A/500V

L2

10uH 6mm

CX1

(Optional) YC 472P/400V (Y1)

Q1

MOSFET 1A/600V

CY1

(Optional) YC 102P/400V (Y1)

R1,R2

R 750KΩ 1206

R4,R3

R 47KΩ 1206

C2

EC 10uF/400V 105℃

C1

CC 103P/500V

R5

R 47Ω 1206

C3

CC 1000P/500V

R6

R 4.7Ω 1206

C4

EC 10u/50V

R7

R 100Ω 0805

C6

CC 472P 0805

R8

C7

(Optional) CC 102P/100V 1206

R10

R 10Ω 1206
(Optional) R 10Ω 1206

C8

EC 470u/10V 105℃

R9

R 100KΩ 0805

C9

EC 220u/10V 105℃

R11

R 100Ω 1/8W

C10

CC 222P 0805

R12

R 33KΩ 0805

D1

Diode FRI07

R13

R 33KΩ 1/8W

D2

Diode FR102

R14

R 4.7KΩ 0805

Diode SB360

T1

EE-16

U1

IC SG6848 (Green PWM IC)

D4
D5

(Optional) ZD 6.8V 0.5W

F1

R 1Ω/0.5W

U2

PC817

L1

20mH 6*8mm

U3

TL431

© System General Corp.
Version 1.2(IRO33.0010.B0)

- 10 -

www.sg.com.tw
May.06, 2003

Product Specification

SG6848

Low Cost Green-Mode PWM Controller for Flyback Converters

PACKAGE INFORMATION
8 PINS -- DIP (D)
D

Θ°

5

E1

8

B

A

A2

4

A1

1

e

E

L
b1

e

b

Dimensions

Symbol

Millimeters
Min.
Typ.

A

Inches
Min.

Max.

Typ.

5.334

A1

0.381

A2

3.175

0.210
0.015

3.302

3.429

0.125

0.130

b

1.524

0.060

b1

0.457

0.018

D

9.017

E
E1

9.271

10.160

0.355

7.620
6.223

e

Max.

6.350

0.365

0.135

0.400

0.300
6.477

0.245

2.540

0.250

0.255

0.100

L

2.921

3.302

3.810

0.115

0.130

0.150

eB

8.509

9.017

9.525

0.335

0.355

0.375

θ˚

0˚

7˚

15˚

0˚

7˚

15˚

© System General Corp.
Version 1.2(IRO33.0010.B0)

- 11 -

www.sg.com.tw
May.06, 2003

Product Specification

SG6848

Low Cost Green-Mode PWM Controller for Flyback Converters

SOT-26 (S)
D

Detail A

b
4

1

e

c

3

e1

1
R
R

θ

L
A1

L1

θ

A

A2

1

L2

E

E1

6

θ

1
Detail A

Dimensions
Symbol

Millimeters
Min.
Typ.

Inches
Min.

Max.

Typ.

Max.

A

1.45

0.057

A1

0.15

0.006

A2

0.90

b
c

1.30

0.036

0.30

0.50

0.011

0.08

0.22

0.003

D

1.15

2.90

0.045

0.020
0.009
0.114

E

2.80

0.110

E1

1.60

0.063

e

0.95

0.037

e1

1.90

0.075

L

0.30

0.45

L1

0.60

L2

0.25

0.051

0.60

0.020

0.018

0.024

0.024
0.010

R

0.10

R1

0.10

0.25

0.004

θ˚

0˚

4˚

8˚

0˚

4˚

8˚

θ1˚

5˚

10˚

15˚

5˚

10˚

15˚

© System General Corp.
Version 1.2(IRO33.0010.B0)

0.004

- 12 -

0.010

www.sg.com.tw
May.06, 2003

Product Specification
Low Cost Green-Mode PWM Controller for Flyback Converters

SG6848

DISCLAIMERS
LIFE SUPPORT
System General’s products are not designed to be used as components in devices intended to support or sustain
human life. Use of System General’s products in components intended for surgical implant into the body, or other
applications in which failure of System General’s products could create a situation where personal death or injury may
occur, is not authorized without the express written approval of System General’s Chief Executive Officer. System
General will not be held liable for any damages or claims resulting from the use of its products in medical applications.

MILITARY
System General's products are not designed for use in military applications. Use of System General’s products in
military applications is not authorized without the express written approval of System General’s Chief Executive Officer.
System General will not be held liable for any damages or claims resulting from the use of its products in military
applications.

RIGHT TO MAKE CHANGES
System General reserves the right to change this document and/or this product without notice. Customers are advised
to consult their System General sales representative before ordering.

© System General Corp.
Version 1.2(IRO33.0010.B0)

- 13 -

www.sg.com.tw
May.06, 2003