STMicroelectronics 19 V - 75 W SMPS using the L6563 and the L6566A EVL6566A-75WES4 EVL6566A-75WES4 Fiche De Données

Doc ID 16116 Rev 4

29/43

V(TBO)/RT, that is internally 1:1 mirrored and sunk from pin INV (#1) input of the L6563S's 
error amplifier. In this way, when the mains voltage increases the voltage at TBO pin will 
increase as well and so will do the current flowing through the resistor connected between 
TBO and GND. Then a larger current will be sunk by INV pin and the output voltage of the 
PFC pre-regulator will be forced to get higher. Obviously, the output voltage will move in the 
opposite direction if the input voltage decreases. 

To avoid undesired output voltage rise should the mains voltage exceed the maximum 
specified value, the voltage at the TBO pin is clamped at 3V. By properly selecting the 
multiplier bias it is possible to set the maximum input voltage above which input-to-output 
tracking ends and the output voltage becomes constant. If this function is not used, leave 
the pin open: the device will regulate a fixed output voltage.

Starting from the following data:

●

Vin

1

 = minimum specified input RMS voltage;

●

Vin

2

 = maximum specified input RMS voltage;

●

Vo

1

 = regulated output voltage @ Vin = Vin

1

;

●

Vo

2

 = regulated output voltage @ Vin = Vin

2

;

●

Vox = absolute maximum limit for the regulated output voltage;

to set the output voltage at the desired values use the following design procedure:

1.

Determine the input RMS voltage Vinclamp that produces Vo = Vox: 

and choose a value Vin

x

 such that Vin

2

 

≤ 

Vinx < Vinclamp. This will result in a limitation 

of the output voltage range below Vox (it will equal Vox if one chooses Vin

x

 = Vin

clamp

)

2. 

Determine the divider ratio of the MULT pin (#3) bias:

and check that at minimum mains voltage Vin1 the peak voltage on pin 3 is greater than 
0.65 V. 

3. 

Determine R1, the upper resistor of the output divider, for instance 3 M

Ω.

4. 

Calculate the lower resistor R2 of the output divider and the adjustment resistor RT:

5. 

Check that the maximum current sourced by the TBO pin (#6) does not exceed the 
maximum specified (0.2 mA): 

 shows the internal block diagram of the tracking boost function.

1

1

2

2

2

1

2

1

clamp

Vin

Vo

Vo

Vo

Vox

Vin

Vo

Vo

Vo

Vox

Vin

⋅

−

−

−

⋅

−

−

=

x

Vin

2

3

k

⋅

=

(

)

(

)

⎪

⎪

⎩

⎪⎪

⎨

⎧

−

−

⋅

⋅

⋅

=

⋅

−

−

⋅

−

−

⋅

⋅

=

1

2

1

2

T

1

2

2

1

1

2

Vo

Vo

Vin

Vin

1

R

k

2

R

Vin

5

.

2

Vo

Vin

5

.

2

Vo

Vin

Vin

1

R

5

.

2

2

R

3

T

max

TBO

10

2

.

0

R

3

I

−

⋅

≤

=