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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
FEATURES
384x series pin-to-pin compatible Linearly decreasing PWM frequency Burst-mode at low/zero load 5uA start-up current 5mA operating current Vcc over voltage protection Cycle-by-cycle current limiting Zero cross-conduction Slew rate controlled high current totem pole output Fast current sense propagation delay Under voltage lockout (UVLO) with hysteresis
start-up current has been reduced to 5uA, and the minimum operating current has been reduced to 5mA. Each SG384xG has a slew rate controlled high current totem pole output, ideally suited for driving a power MOSFET while keeping EMI low. The current-sense propagation delay is typically 50ns, resulting in significantly more effective constant power protection. During normal operation, a SG384xG controller acts as a fixed frequency PWM controller. The PWM frequency can be easily programmed by changing external RT and CT values. The SG384xG includes two Green-mode functions that dramatically reduce power usage, helping the power supply comply with the latest international power saving guidelines. To cut power consumption under light load conditions, the controller's Green-mode function will linearly decrease the PWM frequency in response to decreases in the output load. Under ultra light-load/zero-load conditions, the RT/CT PWM oscillator periodically shuts down, and enters into Burst-mode. This causes the IC's supply voltage to begin gradually dropping. Just before the supply voltage drops below the UVLO voltage threshold, the RT/CT PWM oscillator turns back on, to prevent the supply voltage from going below the UVLO voltage. SG384xG controllers also come with Over Voltage Protection (OVP). This shuts down PWM output if the supply voltage ever exceeds 27V. The SG384xG series comes in 8-pin DIP and SOP packages.
APPLICATIONS
Switching mode power supplies Power converters
DESCRIPTION
The SG348xG series of current-mode PWM controllers combines high performance with Green-mode power saving features. SG348xG controllers are fully pin-to-pin compatible with bipolar UC384x devices, but they have improved features and functionality. SG384xG series controllers are compatible with the BiCMOS fabrication process, enabling the use of low start-up current and operating currents. This feature further improves power conversion efficiency. The minimal
TYPICAL APPLICATION
Green-mode Operation Oscillator Frequency vs. COMP
From bridge rectifier 120~ 380VDC From auxiliary winding RIN 1.5M VCC Rac 10k RT 10k CT 3.3n C21 0.1u COMP OUTPUT VREF CIN 10u
60 50
Oscillator Frequency (Fosc) vs COMP Voltage
R41 100
Fosc (kHz)
40 30 20 10 0 1 1.5 2 COMP VOLTAGE (V) 2.5 3
SG384x
RT/CT VFB GND SENSE
R42 1k C25 100p RS 0.3
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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
MARKING INFORMATION
8 Z: 2, 3
PIN CONFIGURATION
SG384ZGTP
AXXXXXXXYYWWV
T: D = DIP, S = SOP P : Z = Lead Free Null=Regular Package XXXXXXX: Wafer Lot YY: Year; WW: Week V: Assembly Location
COMP VFB SENSE RT/CT
1 2 3 4
8 7 6 5
VREF VCC OUTPUT GND
1
ORDERING INFORMATION
Part Number
SG3842GAD SG3842GAS SG3842G2AD SG3842G2AS SG3843GAD SG3843GAS SG3842GADZ SG3842GASZ SG3842G2ADZ SG3842G2ASZ SG3843GADZ SG3843GASZ 8.9V0.5V 8.1V0.5V 16V1V 10V1V 3.0 3.0 8.9V0.5V 8.1V0.5V 16V1V 10V1V 3.0 3.0 5.0
UVLO Start threshold Stop threshold
AV
5.0 8-Pin DIP
Package
8-Pin SOP 8-Pin DIP 8-Pin SOP 8-Pin DIP 8-Pin SOP 8-Pin DIP(Lead Free) 8-Pin SOP( Lead Free) 8-Pin DIP(Lead Free) 8-Pin SOP( Lead Free) 8-Pin DIP( Lead Free) 8-Pin SOP( Lead Free)
PIN DESCRIPTIONS
Pin No.
1 2 3 4 5 6 7 8
Symbol
COMP VFB SENSE RT/CT GND OUTPUT VCC VREF
Function
Compensation Feedback Current sense Oscillator control Ground Output Power supply Reference voltage
Description
Output of the Error Amplifier and input to the PWM comparator. It is used for feedback loop compensation. Inverting input of the Error Amplifier. It is normally connected to the switching power supply output through a resistor divider. Current sense comparator input. It is internally set to 1V maximum. A voltage proportional to the inductor current is connected to this input. Oscillator RC timing connection. Connecting a resistor RT from this pin to Vref, and a capacitor CT from this pin to ground, programs the oscillator frequency and the maximum output duty cycle. This pin is the combined control circuit ground and power ground. High-power, totem-pole driver output. This output drives the gate of a power MOSFET. Supply voltage input. 5V-reference voltage output.
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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
BLOCK DIAGRAM
ABSOLUTE MAXIMUM RATINGS
Symbol
Vcc Iz VIN ISINK Pd R j-a TJ Ta Tstg TL Supply voltage Zener current FB/SENSE terminal input voltage Error amplifier sink current Power dissipation Thermal resistance Operating junction temperature Operating ambient temperature Storage temperature range Lead temperature (Soldering) ESD Capability, HBM model ESD Capability, Machine model
Parameter
Test Condition
Low impedance source Zener clamp FB, SENSE at Ta<50C Junction-air 10 sec 20 sec DIP SOP DIP SOP
Value
25 28 10 -0.3 to 5.5V 10 800 400 82.5 141 +150 -40 to 125 -65 to +150 260 220 3.0 200 V
Unit
mA V mA mW C/W C C C C kV V
DIP SOP
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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
OPERATING CONDITIONS
Symbol
Vcc CT RT fOSC Ta
Parameter
Supply voltage Oscillation timing capacitor Oscillation timing resistor Oscillation frequency Operating ambient temperature 0.47 2.0 10 -40
Min.
20 10 100 500 105
Max.
Unit
V nF k kHz C
ELECTRICAL CHARACTERISTICS Reference Voltage Section
Symbol
Vref Line Load Vtc Ios Vref Vn S
Parameter
Reference output voltage Line regulation Load current regulation Temperature stability Short-circuit output current Total output variation Output noise voltage Long term stability
Test Condition
Ta=25C, Io=1mA Vcc=10 to 20V Io=1mA to 20mA Line, Load, Temperature f=10Hz to 10kHz , Ta=25C Ta=125C for 1000 hours
Min.
4.75 -30 4.75 -
Typ.
5.0 2 20 0.5 -85 5.0 50 5
Max.
5.25 20 50 -180 5.25 25
Unit
V mV mV mV/C mA V uV mV
Oscillator Section (VFB=0V, SENSE=0V)
Symbol
FOSC FOSC-G Vcomp,H Vcomp,L fdv fdt IDISCHG
Parameter
Oscillator frequency Green-mode frequency (note 1) Comp Voltage that initiates Green-mode Comp Voltage that shuts down PWM Frequency change with Vcc Frequency change with temp. Discharge current
Test Condition
SG3842G, SG3843G SG3842G2 Vsense=0V SG3842G SG3842G2, SG3843G SG3842G SG3842G2, SG3843G Vcc=10 to 20V Ta=-40 to 85C Ta=25C
Min.
49 49 8
Typ.
52 52 12 2.60 2.00 1.40 1.30 0.2 0.02 9
Max.
55 54 16
Unit
kHz kHz kHz V V V V % %/C mA
7
1 12
Note 1: FOSC-G is the last PWM frequency before completely turned off @ Vcc=15V
Error Amplifier Section
Symbol
VFB Iib Avol BW PSRR Isource Isink VH COMP VL COMP
Parameter
Input voltage Input bias current Open-loop voltage gain Unity gain bandwidth Power supply rejection ratio Output source current Output sink current Output voltage Output voltage
Test Condition
Comp=2.5V FB=2.3V,COMP=0V FB=2.7V,COMP=1V FB=2.3V, RL=15K to GND FB=2.7V, RL=15K to VREF
Min.
2.45 45 0.7 50 -0.8 2 6 -
Typ.
2.5 55 1.2 -1.8 6.5 6.6 -
Max.
2.55 0.1 -3 700
Unit
V uA dB MHz dB mA mA V mV
Current Sense Section
Symbol
AV
Parameter
Current sense input voltage gain (n)
Test Condition
SG3842G
Min.
4.60
Typ.
5.00
Max.
5.40
Unit
V/V
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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G2,SG3843G Ta=25C 2.76 0.9
SG3842G/ SG3843G
3.00 -1 50 1.0 3.24 -5 150 1.1 V/V uA nS V
IIB TPD VTH(IS)
Input bias current Delay to output Maximum input signal
Output Section
Symbol
Vol Voh Tr Tf
Parameter
Output voltage low Output voltage high Rising time Falling time
Test Condition
Vcc=15V, Io=20mA Vcc=15V, Io=20mA Ta=25C, CL=1nF Ta=25C, CL=1nF
Min.
13 -
Typ.
50 50
Max.
0.5 150 150
Unit
V V nS nS
Under-Voltage Lockout Section
Symbol
VTH(ON) VTH(OFF)
Parameter
Start threshold voltage Minimum operating voltage
Test Condition
SG3842G SG3843G SG3842G SG3843G
Min.
15 8.4 9 7.6
Typ.
16 8.9 10 8.1
Max.
17 9.4 11 8.6
Unit
V V V V
PWM Section
Symbol
DCY(MAX) DCY(MIN)
Parameter
Maximum duty cycle Minimum duty cycle
Test Condition
SG3842G, SG3842G2, SG3843G FB=5V, COMP=Open
Min.
90 -
Typ.
95 -
Max.
98 0
Unit
% %
Total Standby Current Section
Symbol
ICC ST ICC OP Vz VP
Parameter
Start-up current Operating supply current Power supply zener voltage Power supply protection voltage
Test Condition
SG3842G, Vcc=15V SG3843G, Vcc=8V FB=SENSE=0V, VDD=15V, CL=1000pF Icc=10mA
Min.
25
Typ.
5 3 5.0 28 27
Max.
15 10 6.5 -
Unit
uA uA mA V V
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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
TYPICAL CHARACTERISTICS
SG3842G
Start-up Current (ICC,ST) vs Temperature
4.0 3.5 3.0 ICC,OP( mA ) ICC,ST( uA ) 2.5 2.0 1.5 1.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE ()
Vcc=14.0V
Operating Supply Current (ICC,OP) vs Temperature
6.50 6.00 5.50 5.00 4.50 4.00 3.50 3.00 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE ()
Vcc=15.0V
Reference Voltage (VREF) vs Temperature
5.10 5.05 5.00 VREF( V ) 4.95 4.90 4.85 4.80 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE () VFB( V )
Vcc=15.0V
Error Amp Input Voltage (VFB) vs Temperature
2.53 2.52 2.51 2.50 2.49 2.48 2.47 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE ()
Vcc=15.0V
Oscillator Frequency (Fosc) vs Temperature
54.0
Vcc=15.0V
Maximum Duty Cycle (DMAX) vs Temperature
96.00
53.0
95.50 DMAX( % )
Vcc=15.0V
FOSC( kHz )
52.0
95.00
51.0
94.50
50.0
49.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE ()
94.00 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE ()
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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
Oscillator Discharge Current (IDISCH) vs Temperature
17.00 9.0 16.50 8.5 IDISCH( mA ) 8.0 7.5 7.0 6.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE ()
Vcc=15.0V
Start Threshold Voltage (VTH) vs Temperature
16.00 VTH( V ) 15.50 15.00 14.50 14.00 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE ()
Minimum Operating Voltage (Vcc,min) vs Temperature
10.4 10.2 10.0 Vcc,min( V ) 9.8 9.6 9.4 9.2 9.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE () Vol( V )
Output Voltage Low @ 20mA (Vol) vs Temperature
0.200
0.150
0.100
0.050
0.000 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE ()
Output Voltage High @ Vcc=15V (Voh) vs Temperature
4.0 15.00 14.98 14.96 14.94 Voh( V ) 14.92 14.90 14.88 14.86 14.84 14.82 14.80 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE () 0.0 0 Vcc Current ( uA)
Vcc=15.0V
Start-up Current vs Vcc Supply Voltage
3.0
Temperature=25
2.0
1.0
2
4
6
8
10
12
14
16
Vcc VOLTAGE (V)
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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
Vcc Current vs Vcc Supply Voltage
6 5 Vcc Current ( mA) 4 Fosc-G (kHz) 30 3 2 1 0 0 3 6 9 12 15 18 21 24 27 Vcc VOLTAGE (V) 50
Fosc-G (Green mode) vs Vcc
Temperature=25
40
COMP=1.4V Temperature=25
20
10
0 9 10 11 12 13 14 Vcc VOLTAGE (V)
Oscillator Frequency (Fosc) vs COMP Voltage
60 50
VCC=15V
40 Fosc (kHz) 30 20 10 0 1
Temperature=25
1.5
2 COMP VOLTAGE (V)
2.5
3
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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
SG3843G
Start-up Current (I CC,ST) vs Temperature
5.0 4.5 4.0 ICC,ST (uA) 3.5 3.0 2.5 2.0 1.5 1.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 Vcc=7.76V
Operating Supply Current (I CC,OP) vs Temperature
6.5 6.0 Vcc=15.0V ICC,OP (mA) 5.5 5.0 4.5 4.0 3.5 -40 -25 -10 5 20 35 50 65 80 95 110 125
T EMPERAT URE ()
TEMPERAT URE ()
Reference Voltage (VREF) vs Temperature
5.25 5.20 5.15 5.10 VREF (V)
VFB (V) 2.53
Error Amp Input Voltage (VFB) vs Temperature
Vcc=15.0V
2.52 2.51 2.50 2.49 2.48 2.47
Vcc=15.0V
5.05 5.00 4.95 4.90 4.85 4.80 4.75 -40 -25 -10 5 20 35 50 65 80 95 110 125
-40
-25
-10
5
20
35
50
65
80
95
110
125
T EMPERAT URE ()
T EMPERATURE ()
Oscillator Frequency (F OSC) vs Temperature
61.0 59.0 57.0 FOSC (kHz) DMAX (%) 55.0 53.0 51.0 49.0 47.0 45.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 94.00 -40 94.50 Vcc=13.0V 95.50 96.00
Maximum Duty Cycle (D MAX) vs Temperature
Vcc=13.0V
95.00
-25
-10
5
20
35
50
65
80
95
110
125
TEMPERAT URE ()
T EMPERATURE ()
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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
Oscillator Discharge Current (I DISCH) vs Temperature
Start Threshold Voltage (VTH(ON)) vs Temperature
9.20
9.0 8.5 IDISCH (mA) 8.0 7.5 7.0 6.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 Vcc=15.0V
9.10 9.00 8.90 VTH(ON) (V) 8.80 8.70 8.60 8.50 8.40 8.30 8.20 -40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERAT URE ()
T EMPERAT URE ()
Minimum Operation Voltage (VTH(OFF)) vs Temperature
8.25 8.20 VTH(OFF) (V)
Vol (V)
Output Voltage Low @ 20mA (Vol) vs Temperature
0.20
0.15
8.15 8.10 8.05 8.00 7.95 -40 -25 -10 5 20 35 50 65 80 95 110 125
0.10
0.05
0.00 -40 -25 -10 5 20 35 50 65 80 95 110 125
T EMPERATURE ( )
T EMPERATURE ()
Output Voltage High @ Vcc=15V (Voh) vs Temperature
7
Start-up Current vs Vcc Supply Voltage
15.00 14.98 14.96 14.94 Voh (V) 14.92 14.90 14.88 14.86 14.84 14.82 14.80 -40 -25 -10 5 20 35 50 65 80 95 110 125
0 0 1 2 3 4 5 6 7 8 Vcc Current (uA) 6 5 4 3 2 1 T emperature=25
T EMPERAT URE ()
Vcc VOLTAGE (V)
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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
Start-up Current vs Vcc Supply Voltage
9 8 T emperature=25 7 Vcc Current (mA) 6 5 4 3 2 1 0 0 5 10 15 20 25
Fosc-G (Green-mode) vs Vcc
30 25 20 COMP=1.4V Temperature=25
Fosc-G (kHz)
15 10 5 0 7 8 9 10 11 12 13 14
Vcc VOLTAGE (V)
Vcc VOLT AGE (V)
Oscillator Frequency (Fosc) vs COMP Voltage
60 50 40 Fosc (kHz) 30 20 10 0 1 1.5 2 COMP VOLTAGE(V) 2.5 3
Vcc=15V Temperature=25
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Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
to a pin, but it is internally biased to a fixed 2.5V 2% voltage.
OPERATION DESCRIPTION
SG384xG devices have many advantages over traditional 384x devices and are completely pin-to-pin compatible with them. The following descriptions highlight the advantages and the differences of the SG384xGA designs.
Current Sensing and PWM Limiting
The SG384xG current-sense input is designed for current-mode control. Current-to-voltage conversion is done externally through the current-sense resistor Rs. Under normal operation, the COMP voltage determines the peak-voltage across Rs. VCOMP is the voltage at the pin COMP and n is the current-sense input voltage gain.
Start-up Current
The required start-up current is typically only 5uA. This ultra-low start-up current allows designers to supply the start-up power required by the SG384xG using a high-resistance and a low-wattage start-up resistor. For example, an application using wide input range (100VAC~240VAC) AC-to-DC power adapter could work with a 1.5 M/0.25W resistor, and a 10uF/25V Vcc hold-up capacitor.
I pk =
VCOMP - 1.4 n * xRS
*n = is typically 5 (4.60 ~ 5.40) for the SG3842G standard versions. n = 3 typically (2.76 ~ 3.24) for the SG3842G2, and the SG3843G models.
Operating Current
The operating current has been reduced to 5.0mA. This low operating current results in higher efficiency and reduces the required Vcc hold-up capacitance. This feature is compatible with general 384x series products. A higher n value attenuates the feedback and ensures loop stability under light-load conditions. The inverting input to the SG384xG current-sense comparator is internally clamped to 1V.
Oscillator Operation
The resistor RT and the capacitor CT, both connected to the pin RT/CT, determine the oscillation frequency. The capacitor CT is normally charged to 2.9V through the resistor RT, which is connected to a 5V reference voltage and discharged to 1.3V by a built-in constant current sink. The dead-time is generated during the discharge period.
Under Voltage Lockout (UVLO)
The Under Voltage Lockout (UVLO) function ensures the SG384xG's supply voltage Vcc will be sufficiently high before the output stage is enabled. The turn-on and turn-off threshold voltages are fixed internally at 16V/10V for the SG3842G and at 8.9V/8.1V for the SG3843G. The hysteresis voltage between turn-on and turn-off prevents Vcc from being unstable during power on/off sequencing. At start-up, before the output switch is enabled, the Vcc hold-up capacitor CIN must be charged up to 16V (SG3842G) through the start-up resistor RIN, The ultra-small start-up current of 5uA allows very large resistance values for the resistor RIN to be used, even with low input voltages. For example, if VAC = 90Vrms, RIN can be as large as 1.5 M and still charge the hold-up capacitor CIN. The power dissipation from this larger resistance RIN would then be less than 70mW (0.07W), even under high line conditions (VAC = 240Vrms). After - 12 www.sg.com.tw Jun.28,2004
f ( kHz ) =
1.72 [RT (k )x CT (F )]
Error Amplifier
The error amplifier's inverting input is connected to the FB pin, and the output is connected to the COMP pin. The COMP output is available for external compensation, allowing designers to control the feedback-loop frequency-response. Non-inverting input is not wired out (c) System General Corp. Version 1.4 ( IRO33.0007.B3)
Product Specification BiCMOS Green-Mode PWM Controllers the IC starts-up and begins normal operation, one of the transformer's auxiliary windings generates the supply voltage Vcc, which supplies the operating current of the SG384xG controller.
SG3842G/ SG3843G
There are two factors that determine the PWM frequency: 1. The resistor RT and the capacitor CT determine the RC charge and discharge times, and therefore, the circuit frequency. They are both connected to the pin RT/CT. Internal comparator threshold voltages. Under normal-load conditions, the internal comparator threshold voltages are fixed at 1.3V (Vcomp,L) and 2.9V (Vcomp,H). Under light-load conditions, the Vcomp,H internal threshold voltage gradually increases. This will increase the RC charging/discharging time, therefore decreasing the frequency. Under ultra-light or zero-load conditions, the Vcomp,H voltage is increased to 4.6V. This will put the circuit into the
Oscillator Frequency (Fosc) vs COMP Voltage
60 50
VCC=15V Temperature=25
Slew Rate Controlled Output Driver
The BiCMOS output stage directly drives the external power MOSFET up to the full supply voltage. The output driver, with a low ON-resistance and high current-driving capability, can easily drive an external capacitive load larger than 1000pF. If operating under recommended conditions, the switching frequency can go up to 500kHz. The output stage is designed to ensure zero crossconduction current. This minimizes heat dissipation, increases efficiency, and enhances reliability. The output driver is also slew-rate controlled to minimize EMI.
2.
Fosc (kHz)
Green-Mode: Linearly Decreasing Frequency and Burst-Mode
System General's patented Green-mode function reduces the switching frequency under light-load and zero-load conditions. Modulation of the PWM frequency can reduce power consumption under light-load and zero-load conditions, because the power loss is directly proportional to the switching frequency. Most of the power loss in a power supply occurs due to the switching loss of the transistor, the core loss of the transformer and inductors, and the power loss of the snubber. These sources of power loss all lose power in proportion to the switching frequency. The controller uses the output of the error amplifier as a feedback voltage to calculate load conditions. When the feedback voltage goes below the Green-mode threshold voltage, the switching frequency will be reduced. Under normal-load and high-load conditions, the PWM operates as usual, and the frequency modulation feature does not affect its operation. For example, assuming RT = 10k and RC = 47k, the peak RT/CT voltage would only be:
40 30 20 10 0 1 1.5 2 COMP VOLTAGE (V) 2.5 3
lowest frequency it can operate at. Assuming RT = 10k and CT = 3.3nF, this is about 12kHz. The frequency vs. COMP voltage (feedback from the output load) is shown in Fig.1.
Fig.1 Oscillator Frequency vs. COMP Voltage
If 12kHz is not low enough to meet stand-by power conservation requirements, a shunt resistor RC can be connected in parallel with the capacitor CT between RT/CT and GND. This will allow the SG384xG to enter into burst-mode.
5V x
47 = 4.12V (10 + 47 )
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Product Specification BiCMOS Green-Mode PWM Controllers Since 4.12V is less than the internal Vcomp,H 4.6V voltage under light-load conditions, the RT/CT oscillator would take a long time to charge up to 4.6V. In this situation, the RT/CT oscillator will stop oscillating. When oscillation stops, there is no PWM output. Consequently, the energy required to supply the SG384xG from the auxiliary winding also gets cut off. This causes the supply voltage Vcc to start dropping. If the supply voltage Vcc drops below the UVLO voltage, it will take the SG384xG several hundred milliseconds to start-up. This delay will cause too much fluctuation to the output voltage. To avoid this, the SG384xG will automatically reduce the internal Vcomp,H voltage, turning the RT/CT oscillator back on when the Vcc supply voltage falls within 1.5V of the UVLO voltage. In Burst-mode, the PWM frequency is burst between 0Hz and the light-load tens of kHz region, not over the full frequency range. Fig.2 shows the Green-mode frequency vs. the supply voltage Vcc. The Green-mode frequency is fixed at 12kHz when Vcc is above 11V. When Vcc is below 11V and approaching UVLO, the PWM frequency is gradually increased. This increases the energy supplied to Vcc, and pulls up the Vcc supply voltage to prevent it from dropping below UVLO. These techniques help achieve optimal power savings. The SG384xG can linearly decrease the PWM frequency under light-load conditions, and enter into burst-mode under ultra-light load and zero-load conditions. Linear frequency reduction and burst-mode enable the SG384xG to deliver excellent power savings and load regulation.
Fosc-G (Green mode) vs Vcc
50
SG3842G/ SG3843G
Vcc Over Voltage Protection (OVP)
When the SG384xG's supply voltage increases to 27V due to abnormal conditions, such as an open loop from the photo-coupler, or a short circuit on the output side, the SG384xG will stop PWM output, to protect the entire power supply from being damaged.
Noise Immunity
Noise from the current-sense or the control signal can cause significant pulse-width jitter, particularly under continuous-mode operation. Slope compensation partially alleviates this problem, but the designer should be aware of its presence. The 384x has a single ground pin. High sink current in the output therefore cannot be returned separately. Ceramic bypass capacitors (0.1uF) from Vcc and VREF to ground will provide low-impedance paths for high-frequency transients. For best results, good high-frequency and RF layout practices should be followed. The designer should avoid long PCB traces and component leads. The oscillator, compensation, and filter components should be located near the 384x. In order to minimize noise interference to the oscillator, it is recommended that CT should never be less than 1000pF. Noise caused by the output (pin 6) also causes problems sometimes. This is because the pin is being pulled below ground at turn-off by the external parasitic. This is particularly true when driving a MOSFET. A resistor series connected from the output (pin 6) to the gate of the MOSFET will prevent such output noise.
40
COMP=1.4V Temperature=25
Fosc-G (kHz)
30
20
10
Drop below UVLO
0 9 10 11 12 13 14 Vcc VOLTAGE (V)
Fig.2 Green-mode Frequency vs. Supply Voltage Vcc
(c) System General Corp. Version 1.4 ( IRO33.0007.B3)
- 14 -
www.sg.com.tw Jun.28,2004
Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
(c) System General Corp. Version 1.4 ( IRO33.0007.B3)
- 15 -
www.sg.com.tw Jun.28,2004
Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
REFERENCE CIRCUIT Universal Input, 12V/5A DC Output
P1 2 Vin 1 Q1 2 + C2 C4 1 2 R4 1 D2 3 4 Vb D4 R8 R10 R11 2 7 6 5 C7 R12 1 U1 SG3842G C8 IS 3 2 3 4 + C5 C6 C1 C01 R2 1,2 1,2 8,9 8,9 1 3 R5 L2 2 C3 1 1 2 Vo+ D1 3 TR2 P2 F1
BD1
1
R1 XC1 R3
3L VZ1 1
4 2
4
2
D3 + 1 2 R6
R7 R9
1
2 1
2
Q2 3
5
5
6,7
6,7
FB VRE
O/P R/C
COM
8
R16
4
GND
VCC
R13
R14
VR C10 C11
D5 Vb + 1 DO7 C12 VR 4 3 U2 1 2 R18 U3 R19 Vo+ R20 2 3 C13 2
R17
1
BOM
Symbol
BD1 C1 C2 C3 C4 C5 C6 C12 D1 D2 D3 D4 F1 L1 L2 Q2
Components
BD 1A/600V EC 68u/400V CC 102P/1KV YC 222P EC 1200u/16V EC 680u/16V EC 10u/25V LED ZD 15V 1N4148 2A/250V UU10.5 MOS 2A/600V
Symbol
R1,3 R2 R4 R5 R6 R13 R14 R17 TR2 T1 U1 U2 U3 VZ1 XC1
Components
470K 1/4W 1M 1/4W 43 1/2W 4.7K 1/4W 0.5 1W 10 1/8W 100 1/8W SCK054 EI28 SG384xG 4N35D TL431 VZ XC 0.22u
(c) System General Corp. Version 1.4 ( IRO33.0007.B3)
- 16 -
www.sg.com.tw Jun.28,2004
Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
PACKAGE INFORMATION 8 DIP Outline Dimensions
D
8 5
E1
E
eB
1
4
A1
A2
L b1 b e
Dimensions
Millimeter Min. 0.381 3.175 Inch Min. 0.015 0.125
Symbol A A1 A2 b b1 D E E1 e L eB
Typ.
A
Max. 5.334 3.429
Typ.
Max. 0.210 0.135
9.017 6.223 2.921 8.509 0
3.302 1.524 0.457 9.271 7.620 6.350 2.540 3.302 9.017 7
10.160 6.477 3.810 9.525 15
0.355 0.245 0.115 0.335 0
0.130 0.060 0.018 0.365 0.300 0.250 0.100 0.130 0.355 7
0.400 0.255 0.150 0.375 15
(c) System General Corp. Version 1.4 ( IRO33.0007.B3)
- 17 -
www.sg.com.tw Jun.28,2004
Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
8 SOP Outline Dimensions
8
5
C
1 b
4 e
D
A1
A
Dimensions
Millimeter Min. 1.346 0.101 Inch Min. 0.053 0.004
Symbol A A1 b c D E e F H L
Typ.
0.406 0.203 4.648 0.381 1.270 0.381X45 5.791 0.406 0 6.197 1.270 8 0.228 0.016 0 4.978 3.987 0.183 0.150
(c) System General Corp. Version 1.4 ( IRO33.0007.B3)
H F
E
L
Max. 1.752 0.254
Typ.
Max. 0.069 0.010
0.016 0.008 0.196 0.157 0.050 0.015X45 0.244 0.050 8
- 18 -
www.sg.com.tw Jun.28,2004
Product Specification BiCMOS Green-Mode PWM Controllers
SG3842G/ SG3843G
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 in other applications in which failure of the 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 1.4 ( IRO33.0007.B3)
- 19 -
www.sg.com.tw Jun.28,2004

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