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AN628 APPLICATION NOTE

Pin 3. OVP (Overvoltage protection input). A comparator with a precise 5.1V reference voltage and 250mV of

hysteresis, detects the overvoltage condition and turns the controller in stand-by condition (with low power con-

sumption) and discharges the soft start capacitor. This pin (see fig. 7) has to be externally connected with a

resistive divider (Ra and Rb) to the D.C. output voltage. The divider ratio is defined by the relation:

where:

Figure 7.

Pin 4. IAC (A.C. current input). This pin (see fig. 8) has to be connected through a resistor to the rectified line

multiplier is described at MULT-OUT section (pin8).

Figure 8.

Pin 5.CA-OUT (Current amplifier output). The CA_OUT deliveres its signal to the PWM comparator. An external

network (see fig. 9) defines the suitable loop gain to process the multiplier output and the line current signals.

To avoid oscillation problem (see fig. 10) the maximum inductor current downslope (VO/L) has to be lower than

Ra

Rb

--------

V

O

∆V

OUT

+

5.1V

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

1

–

=

I

IA C

V

I

R

ac

----------

=

V

O

L

-------- R

s

G

ca

V

srp

f

sw

⋅

≤

⋅⋅