AN628 APPLICATION NOTE

6/35

PWM block.

This block, comparing the sawtooth produced by the oscillator, with the reference signal from the C/A output,

modulates its output signal duty-cycle. Its output, by the logic and driver sections, allows the controlled switch

(Q) to modulate the inductor current.

Logic block.

Controls the flow from the PWM and the output with the Auxiliary function signals and soft start.

Driver block.

The driver supplies the gate current to turn on and off the power switch (Q). It delivers up to 1A peak current to

allow high switching frequency applications.

Aux functions.

The Auxiliary functions allow to avoid overstress on power components of the application.

Power supply block.

This circuitry delivers the internal supply and references, recognizes the Undervoltage and Stand-by conditions

to save consumption.

P.F.C. BOOST DESIGN CRITERIA

L4981 PIN DESCRIPTION AND BIASING CIRCUITRY.

Pin 1. P-GND (Power stage ground). This pin, on the pc-board, has to be connected close the external Mosfet

source.

down the output driver when the voltage at IPK input goes down to zero. In the L4981A, to preset the IPK input

Where:

Note: If used with the L4981A, the auxiliary resistor avoids that the current source spread affects the precision

R

ipk

R

S

I

pk

⋅

I

ipk

-------------------

=

R

ipk

R

S

I

pk

⋅

I

aux

-------------------

=

I

aux

V

VREF

R

aux

------------------

=