PWM CONTROL 3A STEP-DOWN CONVERTER
FSP3131
FUNCTIONAL BLOCK DIAGRAM
FUNCTIONAL DESCROPTION
PWM Control
The FSP3131 consists of DC/DC converters that employ a pulse-width modulation (PWM) system. In converters of
the FSP3131, the pulse width varies in a range from 0 to 100%, according to the load current. The ripple voltage
produced by the switching can easily be removed through a filter because the switching frequency remains constant.
Therefore, these converters provide a low-ripple power over broad ranges of input voltage and load current.
Under Voltage Lockout
The under voltage lockout circuit of the FSP3131 assures that the high-side MOSFET driver outputs remain in the off
state whenever the supply voltage drops below 3.3V. Normal operation resumes once VCC rises above 3.5V.
R
DS(ON)
Current Limiting
The current limit threshold is setting by the external resistor connecting from VCC supply to OCSET. The internal
100uA sink current crossing the resistor sets the voltage at the pin of OCSET. When the PWM voltage is less than the
voltage at OCSET, an over-current condition is triggered.
I
LOAD
×=
R
DS(ON)
I
OCSET
×
R
OCSET
See above formula for setting the current limit value
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2007-6-6
FOSLINK [ FOSLINK SEMICONDUCTOR CO.,LTD ]
