SC4812 Datasheet, PDF (1/15 Pages) Semtech Corporation – Current Mode PWM Controller with Integrated Start-up Circuit and Op Amp

SC4812
Current Mode PWM Controller with
Integrated Start-up Circuit and Op Amp
POWER MANAGEMENT
Description
The SC4812 is a highly integrated current mode PWM
controller designed for isolated or non-isolated dc-dc con-
verters in telecommunication and data communication
applications. It minimizes the amount of external discrete
components needed and leads to substantial cost and
space saving converter designs.
The circuitry of the SC4812 includes an integrated high
voltage start-up circuit suitable for telecom/industrial
voltage applications. It is disabled during regular opera-
tion and improves efficiency. Current mode control with
leading-edge blanking simplifies control loop design and
internal ramp compensation circuit stabilizes the current
loop when operating above 50% duty cycle. Internal er-
ror amplifier could be used for non-isolated applications.
Features
‹ Wide input range 12V to 90V
‹ High-voltage start-up circuit
‹ Current mode control
‹ Transconductance error amplifier
‹ Leading-edge blanking
‹ Cycle by cycle current limit
‹ Programmable external soft-start
‹ Thermal shutdown
‹ SO-8 package. Fully WEEE and RoHS compliant
Applications
‹ IP phones, PoE
‹ Telecom isolated converters
‹ Off-line isolated power supplies
‹ Instrumentation power supplies
‹ Battery chargers
Typical Application Circuit
Vin
C2
R2
T1
R1
C3
C4
U1
D1
Vout
C1
Q1
2 _FB
OUT ⁷
SC4812
3 _COMP
CS ⁵
C5
R3
4 _{SS/SHDN GND} 6
R4
R5
C6
Revision: February 6, 2007
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