SC4911 Datasheet, PDF (1/14 Pages) Semtech Corporation – Bias/Primary Side PWM Controller with Ultra Low Start-up Current

SC4911
Bias/Primary Side PWM Controller
with Ultra Low Start-up Current
POWER MANAGEMENT
Description
Features
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.
‹ 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
R1
C1
Vin
C3
R2
C5
R4
R5
R3
C4
C6
U1 SC4911
T1
D2
Vout
C2
3 _FB
OUT ⁷
Q1
4 _COMP
ILIM ⁵
R6
R7
C7
C8
R8
R9
Revision: April 5, 2006
1
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