Bias/Primary Side PWM Controller
with Ultra Low Start-up Current
POWER MANAGEMENT
Description
The SC4911 is a highly integrated bias/primary side PWM
controller designed for off-line or isolated dc-dc convert-
ers in telecommunication and data communication ap-
plications. The high degree of integration minimizes the
amount of discrete parts needed and leads to substan-
tial cost and space saving converter designs.
The circuitry of the SC4911 includes line voltage UVLO
featuring startup current less than 50µA and program-
mable switching frequency. The device supply is derived
from an auxiliary winding on the transformer. The auxil-
iary winding could also provide output feedback informa-
tion if an optocoupler is not used.
SC4911
Features
Programmable switching frequency up to 500kHz
Line UVLO Protection
Undervoltage Lockout
Low startup current (45µA)
Cycle by cycle current limit
8 pin MSOP. Available in Lead-free, fully WEEE and
RoHS compliant
Applications
Telecom isolated converters
Offline isolated power supplies
Instrumentation power supplies
Battery chargers
Typical Application Circuit
D1
C1
C2
C3
R2
R3
R4
C4
C6
U1 SC4911
Q1
1
8
T1
D2
R1
Vin
Vout
C5
R5
LUVLO
3
VCC
FB
OUT
7
4
R7
C7
COMP
GND
RT
ILIM
5
R6
C8
R8
2
R9
Revision: April 5, 2006
6
1
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SC4911
POWER MANAGEMENT
Absolute Maximum Ratings
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified
in the Electrical Characteristics section is not implied.
Parameter
Supply Voltage
Supply Current
Line UVLO Voltage
FB, ILIM and COMP
Output Current Source or Sink
Storage Temperature Range
Junction Temperature Range
Lead Temperature (Soldering) 10 Sec.
ESD Rating (Human Body Model)
Symbol
V
CC
I
CC
Maximum
18
20
V
CC
-0.3 to 6
250
Units
V
mA
V
V
mA
°C
°C
°C
kV
T
STG
T
J
T
LEAD
ESD
-60 to +150
-40 to +150
260
2
Electrical Characteristics
Unless specified: T
A
= T = -40°C to +125°C, V
CC
= 12V, R = 100KΩ, V
FB
= 2.4V, LUVLO = 1.5V.
J
T
Parameter
Pow er Supply
Vcc Turn-On Voltage
Operating Current
Startup Current
VCC Zener Shunt Voltage
Line UVLO
Lockout Threshold
UVLO Hysteresis
Bias Current
Error Amplifier
Feedback Input Voltage
Feedback Input Voltage Regulation
Input Bias Current
Amplifier Transconductance
Amplifier Souce Current
Amplifier Sink Current
Open Loop Voltage Gain
2006 Semtech Corp.
Test Conditions
Min
Typ
Max
Unit
6.0
f
s
= 200kHz, No load
LUVLO = 0.6V
I
CC
= 10mA
15
3.4
45
16
7.0
5.0
80
17
V
mA
µA
V
1.22
1.25
70
1.28
V
mV
nA
V
LUVLO
< 1.25V
100
V
C C
= 12V
V
CC
= 7V to 12V
2.44
2.425
2.50
2.56
2.575
V
V
nA
µmho
µA
µA
dB
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170
1000
500
600
50
2
SC4911
POWER MANAGEMENT
Pin Configuration
TOP VIEW
Ordering Information
Part Number
SC4911IMSTR
P ackag e
MSOP-8
(1)
Temp. Range (T
J
)
-40°C to +125°C
LUVLO
RT
FB
COMP
(MSOP- 8 PIN)
VCC
OUT
GND
ILIM
SC4911IMSTRT
(2)
Notes:
(1) Only available in tape and reel packaging. A reel
contains 2500 devices.
(2) Lead free product. This product is fully WEEE and RoHS
compliant.
Pin Descriptions
Pin #
1
2
3
4
5
6
7
8
Pin Name
LUVLO
RT
FB
COMP
ILIM
GND
OUT
VC C
Line under voltage lockout.
For programming oscillator frequency.
F e e d b a ck.
Feedback compensation.
Current limit sense.
Ground.
Gate drive output. Low during UVLO or LUVLO.
Supply voltage.
Pin Function
Marking Information
Part Number Code (Example: AAxx)
yyww = Date Code (Example: 0012)
xxxx = Semtech Lot No. (Example: E901
xxxx
01-1)
2006 Semtech Corp.
4
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