View SG6848_188602.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

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
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.
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
From bridge rectifier 120~ 380VDC From auxiliary winding RIN 1.5M VDD FB C6 472p OUTPUT CIN 10u
R7 100
SG6848
SENSE R9 95k RI GND RS 4.7
(c) System General Corp. Version 1.2(IRO33.0010.B0)
-1-
www.sg.com.tw May.06, 2003
Product Specification Low Cost Green-Mode PWM Controller for Flyback Converters
SG6848
MARKING DIAGRAMS
PIN CONFIGURATION
SOT-26 MAYWW M: Mask Version Y: Year; WW: Work Week GND FB 1 8 XXXXXXX: Wafer Lot YY: Year; WW: Week V: Assembly Location GATE VDD NC 1 SENSE 1 2 3 4 RI 1 2 3 6 5 4 GATE VDD SENSE
DIP-8 8 7 6 5 GND FB NC RI
XXXXXXXYYWWV
SG6848D
ORDERING INFORMATION
Part Number
SG6848T SG6848D
PWM Frequency
70kHz 70kHz
Package
6-Pin SOT-26 8-pin DIP-8
PIN DESCRIPTIONS
Name
GATE VDD NC SENSE
Pin No.
DIP-8 / (SOT-26)
Type
Driver Output Supply
Function
The totem-pole output driver for driving the power MOSFET. Power supply. NC pin. Current sense. This pin senses the voltage across a resistor. When the voltage reaches
1 / (6) 2 / (5) 3 4 / (4)
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 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 95k resistor Ri results in a 50uA constant current Ii and a 70kHz switching frequency. NC pin.
RI
5 / (3)
Analog Input/Output
NC FB GND
6 7 / (2) 8 / (1) Analog Input Supply
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.
(c) System General Corp. Version 1.2(IRO33.0010.B0)
-2-
www.sg.com.tw May.06, 2003
Product Specification Low Cost Green-Mode PWM Controller for Flyback Converters
SG6848
BLOCK DIAGRAM
GND 8 (1) RI 5 (3)
ON/OFF Driver Internal Bias VDD
1 (6)
GATE
VDD
2 (5)
OSC
SQ R OCP Comp Vlimit ramp
Blanking Circuit
4 (4)
SENSE
+
_
UVLO 16.3V/11.7V Green Mode Controller
Slope Compensation PWM Comp
4.8V
7 (2)
FB
ABSOLUTE MAXIMUM RATINGS
Symbol
VDD
Parameter
DC Supply Voltage * Zener Clamp Zener Current
Value
25 26 10 -0.3 to 6 V -0.3 to 6V 300 150 SOT-26 DIP-8 20 sec 10 sec SOT-26 DIP-8 208.4 82.5 -55 to +150 220 260 3.0 300
Unit
V V mA V V mW C/W C/W C kV V
VFB VSense Pd TJ RJA Tstg TL
Input Voltage to FB Pin Input Voltage to Sense Pin Power Dissipation Operating Junction Temperature Thermal Resistance (Junction to Air) Storage Temperature Range Lead Temperature (Soldering) ESD Capability, HBM Model ESD Capability, Model
* All voltage values, except differential voltages, are given with respect to the network ground terminal.
(c) System General Corp. Version 1.2(IRO33.0010.B0)
-3-
www.sg.com.tw May.06, 2003
Product Specification Low Cost Green-Mode PWM Controller for Flyback Converters
SG6848
RECOMMENDED OPERATING CONDITIONS
Symbol
VDD Ta
Parameter
DC Supply Voltage Operating Ambient Temperature
Value
20 -30 to +85
Unit
V
ELECTRICAL CHARACTERISTICS (TA = 25C, VDD=15V) Feedback Input Section
Symbol
Ioz Vop
Parameter
Zero Duty Cycle Input Current Open Loop Voltage
Test Condition
Min.
Typ.
1.3 4.5
Max.
2.0
Unit
mA V
Current Sense Section
Symbol
Zcs TPD VTH,FLT VTH,VALLEY
Parameter
Input Impedance Delay to Output Current Limit Flatten Threshold Voltage Current Limit Valley Threshold Voltage
Test Condition
Min.
10
Typ.
150 1.0
Max.
200 0.90
Unit
k nsec V V
0.80
0.85
Oscillator Section
Symbol
Fosc Fosc-green Ig In Sg Fdv Fdt
Parameter
Frequency Green-Mode Frequency Green-Mode FB Input Current Green-Mode Start Threshold FB Input Current In = 0.3mA for a Maximum Duty Cycle Green-Mode Modulation Slope Frequency Variation versus VDD Deviation Frequency Variation versus Temp. Deviation
Test Condition
RI=95k RI=95k
Min.
65
Typ.
70 13 1.16 1
Max.
75 15
Unit
kHz kHz mA mA Hz/uA
RI=95k VDD=12 to 20V TA=-30 to 85
300 0.02 2 2
% %
PWM Section
Symbol
DC (MAX) DC (MIN) Bnk
Parameter
Maximum Duty Cycle Minimum Duty Cycle Leading-Edge Blanking Time
Test Condition
Min.
70 -
Typ.
75 1 250
Max.
80 2
Unit
% % nsec
Output Section
Symbol
Vol Voh tr tf VCLAMP
Parameter
Output Voltage Low Output Voltage High Rising Time Falling Time Output Clamp Voltage
Test Condition
VDD=15V, Io=20mA VDD=15V, Io=20mA VDD=15V, CL=1nF VDD=15V, CL=1nF VDD=20V
Min.
8
Typ.
Max.
1.5
Unit
V V nsec nsec V
50 30 15
200 150 17
(c) System General Corp. Version 1.2(IRO33.0010.B0)
-4-
www.sg.com.tw May.06, 2003
Product Specification Low Cost Green-Mode PWM Controller for Flyback Converters
SG6848
Under Voltage Lockout Section
Symbol
VTH(ON) VDD(min)
Parameter
Start Threshold Voltage Min. Operating Voltage
Test Condition
TA=25C TA=25C
Min.
15.3 10.9
Typ.
16.3 11.7
Max.
17.3 12.5
Unit
V V
Total Standby Current Section
Symbol
IDD ST IDD OP
Parameter
Start-up Current Operating Supply Current
Test Condition
VDD=15V VDD=15V
Min.
Typ.
5 2
Max.
30 5
Unit
uA mA
(c) System General Corp. Version 1.2(IRO33.0010.B0)
-5-
www.sg.com.tw May.06, 2003
Product Specification Low Cost Green-Mode PWM Controller for Flyback Converters
SG6848
TYPICAL CHARACTERISTICS
Start-up Threshold Voltage (VTH(ON)) vs Tem perature
17.0 12.2 12.0 16.5 11.8
Min. Operating Voltage (VDD (min)) vs Temperature
VDD (min) (V)
-40 -25 -10 5 20 35 50 65 80 95 110 125
VTH(ON) (V)
16.0
11.6 11.4 11.2 11.0 10.8
15.5
15.0
14.5
10.6 -40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE ( )
TEMPERATURE ( )
Start-up Crrent (IDD ST) vs Tem perature
30 74.0 25 72.5 20
PWM Oscillator Frequency (FOSC) vs Tem perature
FOSC (KHz)
-40 -25 -10 5 20 35 50 65 80 95 110 125
IDD ST (uA)
71.0 69.5 68.0 66.5 65.0 -40 -25 -10 5 20 35 50 65 80 95 110 125
15 10 5 0
TEMPERATURE ( )
TEMPERATURE ( )
Frequency in green m ode (FOSC-green) vs Tem perature
15 14 80 79 78
Max. Duty Cycle (DC(MAX)) vs Tem perature
FOSC-green (KHz)
DC (MAX) (%)
13 12 11 10 9 8 -40 -25 -10 5 20 35 50 65 80 95 110 125
77 76 75 74 73 72 71 70 -40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE ( )
TEMPERATURE ( )
(c) System General Corp. Version 1.2(IRO33.0010.B0)
-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 60
FOSC (KHz)
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)
(c) System General Corp. Version 1.2(IRO33.0010.B0)
-7-
www.sg.com.tw May.06, 2003
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.
switching frequency. Increasing the resistance will reduce the amplitude of the input current and reduce the switching frequency. A 95k resistor Ri results in a 50uA constant current Ii and a 70kHz switching frequency. The relationship between Ri and the switching frequency is:
fPWM =
6650 R I (k )
(kHz )
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 M, 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).
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.
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.
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. 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).
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 (c) System General Corp. Version 1.2(IRO33.0010.B0)
-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 x 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.
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.
(c) System General Corp. Version 1.2(IRO33.0010.B0)
-9-
www.sg.com.tw May.06, 2003
Product Specification Low Cost Green-Mode PWM Controller for Flyback Converters
SG6848
REFERENCE CIRCUIT Circuit
1
L
F1 CX1
2-
1
L1
2
BD1
+4
C1
+
R1 C2
1
C3 R5
R3 R4
10
T1
1,2 2
D4
1 1
L2
2
N
VO
3
R2
22
D1
9
R10
8 5
C7 C8
+
1
U1
1 2 GND FB RI GATE VDD SENSE 6 5 4
R7
D5
2
+
C9
1 3
Q1
7 3,4
C6
3
GND
R6 R8
+
R9 D2
1 2
C4 U2
4 3 1 2
R11
R13 R14
C10 U3
1
CY1
3
R12
2
BOM
Reference
BD1 CX1 CY1 C2 C1 C3 C4 C6 C7 C8 C9 C10 D1 D2 D4 D5 F1 L1
Component
BD 1A/500V
Reference
L2 Q1 R1,R2 R4,R3 R5 R6 R7 R8 R10 R9 R11 R12 R13 R14 T1 U1 U2 U3
Component
10uH 6mm MOSFET 1A/600V R 750K 1206 R 47K 1206 R 47 1206 R 4.7 1206 R 100 0805 R 10 1206
(Optional) YC 472P/400V (Y1) (Optional) YC 102P/400V (Y1) EC 10uF/400V 105 CC 103P/500V CC 1000P/500V EC 10u/50V CC 472P 0805 (Optional) CC 102P/100V 1206 EC 470u/10V 105 EC 220u/10V 105 CC 222P 0805 Diode FRI07 Diode FR102 Diode SB360 (Optional) ZD 6.8V 0.5W R 1/0.5W 20mH 6*8mm
(Optional) R 10 1206 R 100K 0805 R 100 1/8W R 33K 0805 R 33K 1/8W R 4.7K 0805 EE-16 IC SG6848 (Green PWM IC) PC817 TL431
(c) System General Corp. Version 1.2(IRO33.0010.B0)
- 10 -
www.sg.com.tw May.06, 2003
Product Specification Low Cost Green-Mode PWM Controller for Flyback Converters
SG6848
PACKAGE INFORMATION 8 PINS -- DIP (D)
D
8 5
E1
E
eB
1
4
A1
A2
L b1 b e
Dimensions
Millimeters Min. Typ.
0.381 3.175 3.302 1.524 0.457 9.017 6.223 2.921 8.509 0 9.271 7.620 6.350 2.540 3.302 9.017 7 3.810 9.525 15 0.115 0.335 0 6.477 0.245 10.160 0.355 3.429
A
Symbol
A A1 A2 b b1 D E E1 e L eB
Max.
5.334
Inches Min.
0.015 0.125
Typ.
Max.
0.210
0.130 0.060 0.018 0.365 0.300 0.250 0.100 0.130 0.355 7
0.135
0.400 0.255 0.150 0.375 15
(c) System General Corp. Version 1.2(IRO33.0010.B0)
- 11 -
www.sg.com.tw May.06, 2003
Product Specification Low Cost Green-Mode PWM Controller for Flyback Converters
SG6848
SOT-26 (S)
D b 6 4 Detail A
E1
E
1 e1
e
3
c
1
R
A2
A
L A1 L1 1 Detail A
Dimensions
Symbol
A A1 A2 b c D E E1 e e1 L L1 L2 R R1
1
Millimeters Min. Typ.
Max.
1.45 0.15
Inches Min.
Typ.
0.90 0.30 0.08
1.15
1.30 0.50 0.22
0.036 0.011 0.003
0.045
2.90 2.80 1.60 0.95 1.90 0.30 0.45 0.60 0.25 0.10 0.10 0 5 4 10 0.25 8 15 0.004 0.004 0 5 0.60 0.020
0.114 0.110 0.063 0.037 0.075 0.018 0.024 0.010 0.010 4 10 8 15 0.024
(c) System General Corp. Version 1.2(IRO33.0010.B0)
- 12 -
L2
1 R

Max.
0.057 0.006 0.051 0.020 0.009
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.
(c) System General Corp. Version 1.2(IRO33.0010.B0)
- 13 -
www.sg.com.tw May.06, 2003

▲Up To Search▲

Price & Availability of SG6848

	To Download SG6848 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .