PWM CONTROL 2A STEP-DOWN CONVERTER

2007-6-22

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FSP3133

FUNCTIONAL BLOCK DIAGRAM

FUNCTIONAL DESCROPTION

PWM Control

The FSP3133 consists of DC/DC converters that employ a pulse-width modulation (PWM) system. In converters of

the FSP3133, 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 FSP3133 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.

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.

See above formula for setting the current limit value