SYSTEM GENERAL SG6848 Product Specification

O

UTPU

查询SG6848供应商

Product Specification

Low Cost Green-Mode PWM Controller for Flyback Converters SG6848

FEATURES

 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

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.

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 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.

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.

TYPICAL APPLICATI ON

From bridge rectifier

R9 95k

C6 472p

120~ 380VDC

FB

SG6848

VDD

GND

RIN

1.5M

SENSE

T

From auxiliary winding

C

IN

10u

R7 100

R

4.7

S

Product Specification

1

W

Low Cost Green-Mode PWM Controller for Flyback Converters SG6848

MARKING DI A G RA MS

PI N CONFIGURATION

M: Mask Version

MAYW

Y: Year; WW: Work Week

1

8

SG6848D

XXXXXXXYYWWV

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

1

GND

FB

RI

GATE

VDD

NC

SENSE

SOT-26

2

3

DIP-8

1

2

3

4

GATE

6

5

VDD

4

SENSE

GND

8

FB

7

6

NC

5

RI

ORDERING INFORMATION

Part Number PWM Frequency Package

SG6848T 70kHz 6-Pin SOT-26

SG6848D 70kHz 8-pin DIP-8

PIN DESCRIPTI O NS

Name

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

VDD 2 / (5) Supply Power supply.

NC 3 NC pin.

SENSE 4 / (4) Analog Input

RI 5 / (3)

NC 6 NC pin.

FB 7 / (2) Analog Input

GND 8 / (1) Supply Ground.

Pin No.

DIP-8 / (SOT-26)

Type Function

Current s ense. This pin senses the voltage across a resistor. W hen the voltage r eaches

the internal thr eshold, PWM output is disabled. This activates over-curr ent protection.

This pin also pr ovides current amplitude inf ormation for current-mode control.

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

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 fr equency. A 95kΩ resistor R

current I

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

to the internal PW M comparator, so that the PW M comparator c an c ontrol the duty cycle.

and a 70kHz switching frequency.

i

results in a 50uA constant

i

Product Specification

Low Cost Green-Mode PWM Controller for Flyback Converters SG6848

BLOCK DIAGRAM

VDD 2 (5)

GND

8 (1)

+

_

UVLO

16.3V/11.7V

Internal Bias

RI

5 (3)

OSC

Q

S

R

Green Mode Controller

OCP Comp

Slope Compensation

PWM Comp

ON/OFF Driver

Vlimit ramp

VDD

Blanking Circuit

4.8V

1 (6)

4 (4)

7 (2)

GATE

SENSE

FB

ABSOLUTE MAXIMUM RATINGS

Symbol Parameter Value Unit

VDD DC Supply Voltage *

Zener Clamp

Zener Current

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

TJ Operating Junct ion Temperature 150 ℃

RθJA Thermal Resistance (Junction t o Air)

T

Storage Temper ature Range -55 to +150 ℃

stg

T

L

ESD Capability, HBM Model 3.0 kV

ESD Capability, Model 300 V

Lead Temperature (Soldering)

SOT-26 208.4 °C/W

DIP-8 82.5 °C/W

20 sec SOT-26

10 sec DIP-8

25

26

10

220

260

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

V

mA

°C

Product Specification

Low Cost Green-Mode PWM Controller for Flyback Converters SG6848

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 Test Condition Min. Typ. Max. Unit

Ioz Zero Duty Cycle Input Current 1.3 2.0 mA

Vop Open Loop Voltage 4.5 V

Current Sense Section

Symbol Parameter Test Condition Min. Typ. Max. Unit

Zcs Input Impedance 10 kΩ

TPD Delay to Output 150 200 nsec

V

Current Limit Flatten Threshold Voltage 1.0 V

TH,FLT

V

Current Limit Valley Threshold Voltage 0.80 0.85 0.90 V

TH,VALLEY

Oscillator Section

Symbol Parameter Test Condition Min. Typ. Max. Unit

F

Frequenc y RI=95kΩ 65 70 75 kHz

osc

F

Green-Mode Frequenc y RI=95kΩ 13 15 kHz

osc -green

Ig Green-Mode FB Input Current 1.16 mA

In

Sg Green-Mode Modulation Slope RI=95kΩ 300 Hz/uA

Fdv Frequenc y Variation versus VDD Deviation VDD=12 to 20V 0.02 2 %

Fdt Frequenc y Variation versus T emp. D eviation TA=-30 to 85 ℃ 2 %

Green-Mode Start Threshold FB Input Current

= 0.3mA for a Maximum Duty Cycle

I

n

1 mA

PWM Section

Symbol Parameter Test Condition Min. Typ. Max. Unit

DC

Maximum Dut y Cycle 70 75 80 %

(MAX)

DC

Minimum D uty Cycle - 1 2 %

(MIN)

Bnk Leading-Edge Blanking Time 250 nsec

Output Section

Symbol Parameter Test Condition Min. Typ. Max. Unit

Vol Output Voltage Low VDD=15V, Io=20mA 1.5 V

Voh Output Voltage High VDD=15V, Io=20mA 8 V

tr Rising Time VDD=15V, CL=1nF 50 200 nsec

tf Falling Time VDD=15V, CL=1nF 30 150 nsec

V

Output Clamp Voltage VDD=20V 15 17 V

CLAMP

Product Specification

Low Cost Green-Mode PWM Controller for Flyback Converters SG6848

Under Voltage Lockout Section

Symbol Parameter Test Condition Min. Typ. Max. Unit

V

Start Threshold Voltage TA=25°C 15.3 16.3 17.3 V

TH(ON)

V

Min. Operating Voltage TA=25°C 10.9 11.7 12.5 V

DD(min)

Total Standby Current Section

Symbol Parameter Test Condition Min. Typ. Max. Unit

I

Start-up Current VDD=15V 5 30 uA

DD ST

I

Operating Supply Current VDD=15V 2 5 mA

DD OP

Product Specification

Low Cost Green-Mode PWM Controller for Flyback Converters SG6848

TYPICAL CHARAC TE R I S TICS

Start-up Threshold Voltage (V

TH(ON)

Tempe rature

17.0

16.5

16.0

(V)

TH(ON)

15.5

V

15.0

14.5

-40 -25 -10 5 20 35 50 65 80 95 110 125

TE MP ERAT URE (

Start-up Crrent (I

30

25

20

(uA)

15

DD ST

I

10

5

0

-40 -25 -10 5 20 35 50 65 80 95 110 125

) vs Temperature

DD ST

TE MPE RA TURE (

)

℃℃℃℃

)

℃℃℃℃

) vs

Min. Operating Voltage (V

DD (mi n)

) vs

Tempe r ature

12.2

12.0

11.8

11.6

(V)

11.4

DD (min)

11.2

V

11.0

10.8

10.6

-40 -25 -10 5 20 35 50 65 80 95 110 125

TE MPE RA TURE (

)

℃℃℃℃

PWM Oscillator Frequency (F

Tempe r ature

74.0

72.5

71.0

(KHz)

69.5

OSC

F

68.0

66.5

65.0

-40 -25 -10 5 20 35 50 65 80 95 110 125

TEMPERATURE (

) vs

OSC

)

℃℃℃℃

Frequency i n green mode (F

OSC-green

vs Temper ature

15

14

13

12

(KHz)

11

OSC-green

F

10

9

8

-40 -25 -10 5 20 35 50 65 80 95 110 125

TEMPERATURE (

)

℃℃℃℃

)

Max. Duty Cycle (DC

(MAX)

) vs

Tempe rature

80

79

78

77

76

(%)

75

(MAX)

74

DC

73

72

71

70

-40 -25 -10 5 20 35 50 65 80 95 110 125

TEMPERATURE (

)

℃℃℃℃

Product Specification

Low Cost Green-Mode PWM Controller for Flyback Converters SG6848

PWM Oscilla tor Frequency (FOSC) v s.

FB

80

70

60

50

40

(KHz)

OSC

30

F

20

10

0

0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

FB (mA)

Product Specification

Low Cost Green-Mode PWM Controller for Flyback Converters SG6848

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.

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 V

hold-up capacitor would be sufficient for

DD

an AC-to-DC power adapter with a wide input range (100V

to 240VAC).

AC

Operating Current

The operating current has been reduced to 2mA. The low operating current results in higher efficiency and reduces the V

hold-up capacitance requirement.

cc

switching frequency. Increasing the resistance will reduce the amplitude of the input current and reduce the switching frequency. A 95kΩ resistor R constant current I relationship between R

f

PWM

=

and a 70kHz switching frequency. The

i

and the switching frequency is:

i

6650

I

)(kHz

)(kR

Ω

results in a 50uA

i

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.

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

Const ant Output Power Limit

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 t introduce an additional current proportional to t The propagation delay is nearly constant regardless of the input line voltage V 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).

. This propagation delay will

D

D*Vin/Lp

. Higher input line voltages will

IN

.

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 V can be delivered from the auxiliary winding of the main transformer. V start-up process. This UVLO hysteresis window ensures that hold-up capacitor will be adequate to supply V during start-up.

must not drop below 11.7V during this

DD

until power

DD

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.

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:

33.0

Duty

(max)

Duty

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.

Product Specification

Low Cost Green-Mode PWM Controller for Flyback Converters SG6848

REFEREN CE CIRCUIT Circuit

4

GATE

VDD

L1

1 2

C1

6

5

R7

C3

Q1

R6

R5

D1

D2

R3

R4

21

T1

9

8 5

7 3,4

1,210

D4

2 1

R10

R11

C8

C7

+

L2

1 2

D5

2 1

VO

+

C9

GND

R1

+

C2

R2

2 1 23

1

R8

+

C4

L

N

F1

CX1

C6

1

BD1

-+

2

3

U1

1

GND

2

FB

3 4

RI SENSE

R9

U2

4

3

CY1

1

2

R14

3

U3

1

2

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

C2 EC 10uF/400V 105℃ R4,R3 R 47KΩ 1206

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 R 10Ω 1206

C7 (Optional) CC 102P/100V 1206 R10 (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

D4 Diode SB360 T1 EE-16

D5 (Optional) ZD 6.8V 0.5W U1 IC SG6848 (Green PWM IC)

F1 R 1Ω/0.5W U2 PC817

L1 20mH 6*8mm U3 TL431

R13

C10

R12

Product Specification

Low Cost Green-Mode PWM Controller for Flyback Converters SG6848

PACKAGE INFORMATION 8 PINS -- DIP (D)

D

°

85

Θ

Dimensions

E1

41

A2

A1

L

b1

e

b

Symbol

A 5.334 0.210

A1 0.381 0.015

A2 3.175 3.302 3.429 0.125 0.130 0.135

b 1.524 0.060

b1 0.457 0.018

D 9.017 9.271 10.160 0.355 0.365 0.400

E 7.620 0.300

E1 6.223 6.350 6.477 0.245 0.250 0.255

e 2.540 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˚

Millimeters Inches Min. Typ. Max. Min. Typ. Max.

E

A

eB

Product Specification

Low Cost Green-Mode PWM Controller for Flyback Converters SG6848

SOT-26 (S)

D

b

64

Detail A

Dimensions

E

1

e

e1

A

Symbol

A 1.45 0.057

A1 0.15 0.006

A2 0.90 1.15 1.30 0.036 0.045 0.051

b 0.30 0.50 0.011 0.020

c 0.08 0.22 0.003 0.009

D 2.90 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 0.60 0.020 0.018 0.024

L1 0.60 0.024

L2 0.25 0.010

R 0.10 0.004

R1 0.10 0.25 0.004 0.010

θ˚ 0˚ 4˚ 8˚ 0˚ 4˚ 8˚

θ1˚ 5˚ 10˚ 15˚ 5˚ 10˚ 15˚

A1

A2

θ

1

Millimeters Inches Min. Typ. Max. Min. Typ. Max.

E1

3

θ

1

c

1

R

L

L1

Detail A

L2

R

θ

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.