OVER VOLTAGE PROTECTION OVP

The output voltage is expected to be kept by the

operation of the PFC circuits close to its reference

value that is set by the ratio of the two external re-

eration that the non inverting input of the error

amplifier is biased inside the L6560 at 2.5V.

In steady state conditions, the current through R1

and R2 is:

=

R1

2.5

R2

and, if the external compensation network is

made only with a capacitor C, the current through

C is equal zero.

When the output voltage increases abruptly the

current through R1 becomes:

=

− 2.5

R1

R1

Since the current through R2 doesn’t change, the

∆I current must flow through the capacitor C and

enter in the error amplifier.

This current is mirrored inside the L6560, and

compared with a precise internal reference of

40

µA. Whenever such 40µA limit is exceed, the

OVP protection is triggered (Dynamic OVP), and

the external power transistor is switched off, until

the overvoltage situation disappears. However if

the overvoltage persists, before that the transient

condition of dynamic circuit exhausts, an internal

comparator (Static OVP) latches the OVP condi-

tion keeping the external power switch turned off

(see fig. 1).

The OVP value is threfore set by the equation

OVP =

the application circuit. The overvoltage can be set

independently from the average output voltage.

The precision in setting the overvoltage threshold

is 7% of the overvoltage value (for instance

∆V=

60V

± 4.2V).

ELECTRICAL CHARACTERISTICS (continued)

ZERO CURRENT DETECTOR

Symbol

Pin

Parameter

Test Condition

Min.

Typ.

Max.

Unit

5

Input Threshold Voltage Rising

Edge

1.8

2.3

V

Hysteresis

0.3

0.5

0.7

V

5

Clamp Voltage

5

5.7

6.4

V

5

Clamp Voltage

0.4

0.7

1

V

OUTPUT SECTION

Symbol

Pin

Parameter

Test Condition

Min.

Typ.

Max.

Unit

7

Dropout Voltage

1.2

2

V

0.7

1

V

1.5

V

0.3

V

7

Output Voltage Rise Time

CL = 1nF

50

120

ns

7

Output Voltage Fall Time

CL = 1nF

40

100

ns

OUTPUT OVERVOLTAGE SECTION

Symbol

Pin

Parameter

Test Condition

Min.

Typ.

Max.

Unit

2

OVP Triggering Current

36

40

44

µA

RESTART TIMER

Symbol

Pin

Parameter

Test Condition

Min.

Typ.

Max.

Unit

Start Timer

45

60

µs

L6560 - L6560A

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