SC4905A Datasheet, PDF (1/20 Pages) Semtech Corporation – HIGH PERFORMANCE VOLTAGE MODE PWM CONTROLLER

POWER MANAGEMENT
Description
The SC4905A/B is a 10 pin BICMOS primary side voltage
mode controller for use in Isolated DC-DC and off-line
switching power supplies. It is a highly integrated solution,
requiring few external components. The device features a
high speed oscillator with integrated feed forward
compensation, accurately programmable maximum duty
cycle, voltage mode of operation, line voltage monitoring,
supply UVLO, low start up current, low voltage current limit
threshold and user accessible reference.
The SC4905A/B device operates at a fixed frequency,
highly desirable for Telecom applications. Features a
separate SYNC pin which simplifies synchronization to
an external clock. Feeding the oscillator of one device to
the SYNC of another forces biphase operation (180
degrees apart) which reduces input ripple and filter size.
The SC4905A has a turn-on threshold of 4.5V and the
SC4905B has a turn-on threshold of about 12 volts.
These devices are available in the 10 lead MSOP package.
SC4905A/B
High Performance Voltage Mode
PWM Controller
PRELIMINARY
Features
K Operation to 1MHz
K Accurate programmable maximum duty cycle
K Integrated oscillator/voltage feed forward
compensation
K Line voltage monitoring
K External frequency synchronization
K Bi-phase mode of operation for ripple reduction
K Under 100µA start-up current
K Accessible reference voltage
K VDD undervoltage lockout
K -40°C to 105°C operating temperature
K 10 lead MSOP package
Applications
K Telecom equipment and power supplies
K Networking power supplies
K Power over LAN applications
K Industrial power supplies
K Isolated power supplies
Typical Application Circuit
Revision 4, April 2002
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