ETC SG3842GAD

Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
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
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
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.
TYPICAL APPLICATION
Green-mode Operation
Oscillator Frequency vs. COMP
From bridge rectifier
120~ 380VDC
From auxiliary winding
RIN
1.5M
Oscillator Frequency (Fosc) vs COMP Voltage
CIN
10u
60
50
VCC
COMP
Rac
10k
RT
10k
CT
3.3n
R41
100
40
Fosc (kHz)
OUTPUT
VREF
C21
0.1u
SG384x
C25
100p
10
RS
0.3
0
1
GND
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
30
20
SENSE
RT/CT
VFB
R42
1k
1.5
2
2.5
3
COMP VOLTAGE (V)
-1-
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
MARKING INFORMATION
PIN CONFIGURATION
8
Z: 2, 3
T: D = DIP, S = SOP
SG384ZGTP
AXXXXXXXYYWWV
COMP
1
8
VREF
VFB
2
7
VCC
XXXXXXX: Wafer Lot
SENSE
3
6
OUTPUT
YY: Year; WW: Week
RT/CT
4
5
GND
P : Z = Lead Free
Null=Regular Package
1
V: Assembly Location
ORDERING INFORMATION
Part Number
UVLO
Start threshold
Stop threshold
AV
SG3842GAD
5.0
SG3842GAS
SG3842G2AD
16V±1V
10V±1V
3.0
SG3842G2AS
SG3843GAD
8.9V±0.5V
SG3843GAS
8.1V±0.5V
3.0
SG3842GADZ
SG3842GASZ
SG3842G2ADZ
5.0
16V±1V
10V±1V
3.0
SG3842G2ASZ
SG3843GADZ
SG3843GASZ
8.9V±0.5V
8.1V±0.5V
3.0
Package
8-Pin DIP
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.
Symbol
Function
1
COMP
Compensation
2
VFB
Feedback
3
SENSE
Current sense
4
RT/CT
Oscillator control
5
6
7
8
GND
OUTPUT
VCC
VREF
Ground
Output
Power supply
Reference voltage
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
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.
-2-
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
BLOCK DIAGRAM
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Vcc
Supply voltage
Iz
VIN
ISINK
Zener current
FB/SENSE terminal input voltage
Error amplifier sink current
Pd
Power dissipation
RΘ j-a
Thermal resistance
TJ
Ta
Tstg
Operating junction temperature
Operating ambient temperature
Storage temperature range
TL
Lead temperature (Soldering)
Test Condition
Low impedance source
Zener clamp
FB, SENSE
at Ta<50°C
Junction-air
10 sec
20 sec
ESD Capability, HBM model
ESD Capability, Machine model
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
-3-
DIP
SOP
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
Unit
V
mA
V
mA
mW
°C/W
°C
°C
°C
°C
kV
V
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
OPERATING CONDITIONS
Symbol
Vcc
CT
RT
fOSC
Ta
Parameter
Min.
Supply voltage
Oscillation timing capacitor
Oscillation timing resistor
Oscillation frequency
Operating ambient temperature
0.47
2.0
10
-40
Max.
Unit
20
10
100
500
105
V
nF
kΩ
kHz
°C
ELECTRICAL CHARACTERISTICS
Reference Voltage Section
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
Vref
Line
Load
Vtc
Ios
Vref
Vn
S
Reference output voltage
Line regulation
Load current regulation
Temperature stability
Short-circuit output current
Total output variation
Output noise voltage
Long term stability
Ta=25°C, Io=1mA
Vcc=10 to 20V
Io=1mA to 20mA
Line, Load, Temperature
f=10Hz to 10kHz , Ta=25°C
Ta=125°C for 1000 hours
4.75
-30
4.75
-
5.0
2
20
0.5
-85
5.0
50
5
5.25
20
50
-180
5.25
25
V
mV
mV
mV/°C
mA
V
uV
mV
Oscillator Section (VFB=0V, SENSE=0V)
Symbol
Parameter
FOSC
Oscillator frequency
FOSC-G
Green-mode frequency (note 1)
Vcomp,H
Comp Voltage that initiates Green-mode
Vcomp,L
Comp Voltage that shuts down PWM
fdv
fdt
IDISCHG
Frequency change with Vcc
Frequency change with temp.
Discharge current
Test Condition
Min.
Typ.
Max.
Unit
SG3842G, SG3843G
SG3842G2
Vsense=0V
SG3842G
SG3842G2, SG3843G
SG3842G
SG3842G2, SG3843G
Vcc=10 to 20V
Ta=-40 to 85°C
Ta=25°C
49
49
8
52
52
12
2.60
2.00
1.40
1.30
0.2
0.02
9
55
54
16
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
Parameter
Test Condition
Min.
Typ.
Max.
Unit
VFB
Iib
Avol
BW
PSRR
Isource
Isink
VH COMP
VL COMP
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
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
2.45
45
0.7
50
-0.8
2
6
-
2.5
55
1.2
-1.8
6.5
6.6
-
2.55
0.1
-3
700
V
uA
dB
MHz
dB
mA
mA
V
mV
Current Sense Section
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
AV
Current sense input voltage gain (n)
SG3842G
4.60
5.00
5.40
V/V
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
-4-
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
IIB
TPD
VTH(IS)
Input bias current
Delay to output
Maximum input signal
SG3842G2,SG3843G
Ta=25°C
-
2.76
0.9
3.00
-1
50
1.0
3.24
-5
150
1.1
V/V
uA
nS
V
Output Section
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
Vol
Output voltage low
Vcc=15V, Io=20mA
-
-
0.5
V
Voh
Tr
Tf
Output voltage high
Rising time
Falling time
Vcc=15V, Io=20mA
Ta=25°C, CL=1nF
Ta=25°C, CL=1nF
13
-
50
50
150
150
V
nS
nS
Test Condition
Min.
Typ.
Max.
Unit
SG3842G
SG3843G
SG3842G
SG3843G
15
8.4
9
7.6
16
8.9
10
8.1
17
9.4
11
8.6
V
V
V
V
Test Condition
Min.
Typ.
Max.
Unit
SG3842G, SG3842G2,
SG3843G
FB=5V, COMP=Open
90
95
98
%
-
-
0
%
Test Condition
Min.
Typ.
Max.
Unit
SG3842G, Vcc=15V
SG3843G, Vcc=8V
FB=SENSE=0V, VDD=15V,
CL=1000pF
Icc=10mA
-
5
3
15
10
uA
uA
-
5.0
6.5
mA
25
28
27
-
V
V
Under-Voltage Lockout Section
Symbol
Parameter
VTH(ON)
Start threshold voltage
VTH(OFF)
Minimum operating voltage
PWM Section
Symbol
Parameter
DCY(MAX)
Maximum duty cycle
DCY(MIN)
Minimum duty cycle
Total Standby Current Section
Symbol
Parameter
ICC ST
Start-up current
ICC OP
Operating supply current
Vz
VP
Power supply zener voltage
Power supply protection voltage
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
-5-
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
TYPICAL CHARACTERISTICS
SG3842G
Start-up Current (ICC,ST ) vs Temperature
Operating Supply Current (ICC,OP) vs Temperature
4.0
6.50
Vcc=14.0V
3.5
5.50
ICC,OP( mA )
3.0
ICC,ST( uA )
Vcc=15.0V
6.00
2.5
2.0
5.00
4.50
4.00
1.5
3.50
1.0
3.00
-40
-25
-10
5
20
35
50
65
80
95
110
125
-40
-25
-10
5
TEMPERATURE (℃)
35
50
65
80
95
110
125
TEMPERATURE (℃)
Reference Voltage (VREF) vs Temperature
Error Amp Input Voltage (VFB) vs Temperature
5.10
2.53
Vcc=15.0V
5.05
Vcc=15.0V
2.52
2.51
VFB( V )
5.00
VREF( V )
20
4.95
2.50
4.90
2.49
4.85
2.48
4.80
2.47
-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 (℃)
Oscillator Frequency (Fosc) vs Temperature
Maximum Duty Cycle (DMAX) vs Temperature
54.0
96.00
Vcc=15.0V
Vcc=15.0V
95.50
52.0
DMAX( % )
FOSC( kHz )
53.0
51.0
95.00
94.50
50.0
94.00
49.0
-40
-25
-10
5
20
35
50
65
80
95
110
-40
125
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
-25
-10
5
20
35
50
65
80
95
110
125
TEMPERATURE (℃)
TEMPERATURE (℃)
-6-
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
Oscillator Discharge Current (IDISCH) vs
Temperature
Start Threshold Voltage (VTH) vs Temperature
17.00
9.0
16.50
Vcc=15.0V
16.00
VTH( V )
IDISCH( mA )
8.5
8.0
15.50
7.5
15.00
7.0
14.50
14.00
6.5
-40
-25
-10
5
20
35
50
65
80
95
110
-40
125
-25
-10
5
20
35
50
65
80
95
110
125
TEMPERATURE (℃)
TEMPERATURE (℃)
Minimum Operating Voltage (Vcc,min) vs
Temperature
Output Voltage Low @ 20mA (Vol) vs Temperature
0.200
10.4
10.2
0.150
Vol( V )
Vcc,min( V )
10.0
9.8
9.6
9.4
0.100
0.050
9.2
0.000
9.0
-40
-25
-10
5
20
35
50
65
80
95
110
-40
125
-25
-10
5
20
35
50
65
80
95
110
125
TEMPERATURE (℃)
TEMPERATURE (℃)
Output Voltage High @ Vcc=15V (Voh) vs
Temperature
Start-up Current vs Vcc Supply Voltage
4.0
15.00
14.98
14.96
3.0
Vcc Current ( uA)
Vcc=15.0V
Voh( V )
14.94
14.92
14.90
14.88
14.86
Temperature=25℃
2.0
1.0
14.84
14.82
0.0
14.80
-40
-25
-10
5
20
35
50
65
80
95
110
0
125
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
2
4
6
8
10
12
14
16
Vcc VOLTAGE (V)
TEMPERATURE (℃)
-7-
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
Fosc-G (Green mode) vs Vcc
Vcc Current vs Vcc Supply Voltage
6
50
Temperature=25℃
40
COMP=1.4V
4
Temperature=25℃
Fosc-G (kHz)
Vcc Current ( mA)
5
3
2
30
20
10
1
0
0
0
3
6
9
12
15
18
21
24
27
9
Vcc VOLTAGE (V)
10
11
12
13
14
Vcc VOLTAGE (V)
Oscillator Frequency (Fosc) vs COMP Voltage
60
50
VCC=15V
Fosc (kHz)
40
Temperature=25℃
30
20
10
0
1
1.5
2
2.5
3
COMP VOLTAGE (V)
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
-8-
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
SG3843G
Start-up Current (I CC,ST) vs Temperature
Operating Supply Current (I CC,OP) vs
Temperature
5.0
6.5
4.5
Vcc=7.76V
6.0
Vcc=15.0V
3.5
I CC ,OP (mA)
I CC ,ST (uA)
4.0
3.0
2.5
2.0
5.5
5.0
4.5
4.0
1.5
1.0
3.5
-40
-25
-10
5
20
35
50
65
80
95
110
125
-40
-25
-10
5
20
T EMPERAT URE (℃)
Reference Voltage (VREF) vs Temperature
50
65
80
95
110
125
Error Amp Input Voltage (VFB) vs Temperature
2.53
5.25
5.20
Vcc=15.0V
Vcc=15.0V
2.52
5.15
5.10
2.51
5.05
V FB (V)
V R EF (V)
35
TEMPERAT URE (℃)
5.00
2.50
4.95
2.49
4.90
4.85
2.48
4.80
2.47
4.75
-40
-25
-10
5
20
35
50
65
80
95
110
-40
125
-25
-10
5
35
50
65
80
95
110
125
Maximum Duty Cycle (D MAX) vs Temperature
Oscillator Frequency (F OSC) vs Temperature
96.00
61.0
59.0
Vcc=13.0V
Vcc=13.0V
57.0
95.50
55.0
DMAX (%)
FOSC (kHz)
20
T EMPERATURE (℃)
T EMPERAT URE (℃)
53.0
95.00
51.0
49.0
94.50
47.0
45.0
94.00
-40
-25
-10
5
20
35
50
65
80
95
110
-40
125
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
-25
-10
5
20
35
50
65
80
95
110
125
T EMPERATURE (℃)
TEMPERAT URE (℃)
-9-
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
Start Threshold Voltage (VTH(ON)) vs Temperature
Oscillator Discharge Current (I DISCH) vs
Temperature
9.20
9.10
9.0
9.00
Vcc=15.0V
8.90
V TH(ON) (V)
ID ISC H (mA)
8.5
8.0
7.5
8.80
8.70
8.60
8.50
7.0
8.40
8.30
6.5
-40
-25
-10
5
20
35
50
65
80
95
110
8.20
125
-40
-25
-10
5
TEMPERAT URE (℃)
20
35
50
65
80
95
110
125
T EMPERAT URE (℃)
Minimum Operation Voltage (VTH(OFF)) vs
Temperature
Output Voltage Low @ 20mA (Vol) vs Temperature
0.20
8.25
0.15
8.15
Vol (V)
VTH(OFF) (V)
8.20
8.10
8.05
0.10
0.05
8.00
0.00
7.95
-40
-25
-10
5
20
35
50
65
80
95
-40
110 125
-25
-10
5
20
35
50
65
80
95
110
125
T EMPERATURE (℃)
T EMPERATURE (℃ )
Output Voltage High @ Vcc=15V (Voh) vs
Temperature
Start-up Current vs Vcc Supply Voltage
7
15.00
6
14.98
Vcc Current (uA)
14.96
Voh (V)
14.94
14.92
14.90
14.88
T emperature=25℃
5
4
3
14.86
2
14.84
1
14.82
0
14.80
-40
-25
-10
5
20
35
50
65
80
95
110
0
125
T EMPERAT URE (℃)
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
1
2
3
4
5
6
7
8
Vcc VOLTAGE (V)
- 10 -
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
Start-up Current vs Vcc Supply Voltage
Fosc-G (Green-mode) vs Vcc
30
9
8
25
T emperature=25℃
COMP=1.4V
Temperature=25℃
Vcc Current (mA)
7
20
Fosc-G (kHz)
6
5
4
15
10
3
2
5
1
0
0
0
5
10
15
20
7
25
8
9
10
11
12
13
14
Vcc VOLTAGE (V)
Vcc VOLT AGE (V)
Oscillator Frequency (Fosc) vs COMP Voltage
60
50
Vcc=15V
Temperature=25℃
Fosc (kHz)
40
30
20
10
0
1
1.5
2
2.5
3
COMP VOLTAGE(V)
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
- 11 -
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
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.
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 MΩ/0.25W resistor, and a 10uF/25V Vcc
hold-up capacitor.
to a pin, but it is internally biased to a fixed 2.5V ± 2%
voltage.
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.
I pk =
VCOMP − 1.4
n * ×RS
*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.
f ( kHz ) =
1.72
[RT (kΩ )× CT (µF )]
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
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
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 MΩ 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
Product Specification
SG3842G/ SG3843G
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.
Slew Rate Controlled Output Driver
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.
2.
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
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.
Oscillator Frequency (Fosc) vs COMP Voltage
VCC=15V
60
Temperature=25℃
50
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.
40
Fosc (kHz)
Green-Mode: Linearly Decreasing
Frequency and Burst-Mode
20
10
0
1
For example, assuming RT = 10kΩ and RC = 47kΩ, the
peak RT/CT voltage would only be:
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
1.5
2
2.5
3
COMP VOLTAGE (V)
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.
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.
30
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 ×
- 13 -
47
= 4.12V
(10 + 47 )
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Jun.28,2004
Product Specification
SG3842G/ SG3843G
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
COMP=1.4V
Temperature=25℃
Fosc-G (kHz)
40
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.
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
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
- 14 -
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
- 15 -
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
REFERENCE CIRCUIT
Universal Input, 12V/5A DC Output
2
P1
1
R1
3 L
4
1
2
4
Vin
BD1
1
VZ1
Q1
R4
R2
1,2
1,2
8,9
8,9
TR2
F1
C4
1
2
2
3
4
D3
+ C5
3
4
+
C6
D4
1
2
R8
Q2
1
R9
5
GND
2
6
O/P
R/C
R16
U1 SG3842G
6,7
3
D5
VR
1
Vb
C10
5
R14
R13
C8
IS
R6
6,7
4
VCC
COM
8
1
FB
VRE
R11
R12
7
R10
C7
5
3
R7
2
2
2
Vb
Vo+
D1
D2
1
1
2
C3
R5
1
P2
L2
1
3
1
3
+ C2
2
C1
C01
2
XC1
R3
2
C11
+
DO7
C12
VR
U2
4
1
3
2
R18
3
R17
C13
U3
R19
1
Vo+
2
R20
BOM
Symbol
Components
Symbol
Components
BD1
C1
C2
C3
C4
C5
C6
C12
D1
D2
D3
D4
F1
L1
L2
Q2
BD 1A/600V
R1,3
R2
R4
R5
R6
R13
R14
R17
TR2
T1
U1
U2
U3
VZ1
XC1
470K 1/4W
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
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
MOS 2A/600V
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
- 16 -
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
PACKAGE INFORMATION
8 DIP Outline Dimensions
D
Θ°
5
E1
8
B
A
A2
4
A1
1
e
E
L
b1
b
e
Dimensions
Symbol
A
A1
A2
b
b1
D
E
E1
e
L
eB
θ˚
Millimeter
Min.
0.381
3.175
9.017
6.223
2.921
8.509
0˚
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
Inch
Min.
Typ.
Max.
5.334
3.302
1.524
0.457
9.271
7.620
6.350
2.540
3.302
9.017
7˚
3.429
0.015
0.125
10.160
0.355
6.477
0.245
3.810
9.525
15˚
0.115
0.335
0˚
- 17 -
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˚
www.sg.com.tw
Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
8 SOP Outline Dimensions
C
5
E
H
8
F
1
4
b
e
D
Θ
A1
L
A
Dimensions
Symbol
A
A1
b
c
D
E
e
F
H
L
θ˚
Millimeter
Min.
1.346
0.101
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
Typ.
Max.
1.752
0.254
Inch
Min.
0.053
0.004
0.406
0.203
4.648
0.381
Max.
0.069
0.010
0.016
0.008
4.978
3.987
0.183
0.150
1.270
0.196
0.157
0.050
0.381X45˚
5.791
0.406
0˚
Typ.
0.015X45˚
6.197
1.270
8˚
- 18 -
0.228
0.016
0˚
0.244
0.050
8˚
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Jun.28,2004
Product Specification
SG3842G/ SG3843G
BiCMOS Green-Mode PWM Controllers
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.
© System General Corp.
Version 1.4 ( IRO33.0007.B3)
- 19 -
www.sg.com.tw
Jun.28,2004