L6561
ELECTRICAL CHARACTERISTICS
(continued)
ZERO CURRENT DETECTOR
Symbol
V
ZCD
Pin
5
Parameter
Input Threshold Voltage
Rising Edge
Hysteresis
V
ZCD
V
ZCD
V
ZCD
I
ZCD
I
ZCD
I
ZCD
V
DIS
I
ZCD
5
5
5
5
5
5
5
5
Upper Clamp Voltage
Upper Clamp Voltage
Lower Clamp Voltage
Sink Bias Current
Source Current Capability
Sink Current Capability
Disable threshold
Restart Current After Disable
V
ZCD
< Vdis; V
CC
> V
CCOFF
(1)
(1)
I
ZCD
= 20µA
I
ZCD
= 3mA
I
ZCD
= –3mA
1V
≤
V
ZCD
≤
4.5V
-3
3
150
-100
200
-200
0.3
4.5
4.7
0.3
Test Condition
Min.
Typ.
2.1
0.5
5.1
5.2
0.65
2
-10
10
250
-300
0.7
5.9
6.1
1
Max.
Unit
V
V
V
V
V
µ
A
mA
mA
mV
µA
OUTPUT SECTION
V
GD
7
Dropout Voltage
I
GDsource
= 200mA
I
GDsource
= 20mA
I
GDsink
= 200mA
I
GDsink
= 20mA
t
r
t
f
I
GD off
7
7
7
Output Voltage Rise Time
Output Voltage Fall Time
I
GD
Sink Current
C
L
= 1nF
C
L
= 1nF
V
CC
=3.5V V
GD
= 1V
5
40
40
10
1.2
0.7
2
1
1.5
0.3
100
100
-
V
V
V
V
ns
ns
mA
µA
V
µs
OUTPUT OVERVOLTAGE SECTION
I
OVP
2
OVP Triggering Current
Static OVP Threshold
35
2.1
40
2.25
45
2.4
RESTART TIMER
t
START
Start Timer
70
150
400
(1) Parameter guaranteed by design, not tested in production.
OVER VOLTAGE PROTECTION OVP
The output voltage is expected to be kept by the
operation of the PFC circuit close to its nominal
value. This is set by the ratio of the two external
resistors R
1
and R
2
(see fig. 2), taking into con-
sideration that the non inverting input of the error
amplifier is biased inside the L6561 at 2.5V.
In steady state conditions, the current through R1
and R2 is:
I
R1sc
=
V
out
−
2.5
2.5V
=
I
R2
=
R1
R2
and, if the external compensation network is
made only with a capacitor C
comp
, the current
through C
comp
equals zero.
When the output voltage increases abruptly the
current through R1 becomes:
I
R1
=
4/11
V
outsc
+ ∆V
OUT
−
2.5
=
I
R1sc
+ ∆
I
R1
R1
Since the current through R2 does not change,
∆
I
R1
must flow through the capacitor C
comp
and
enter the error amplifier.
This current is monitored inside the L6561 and when
reaches about 37µA the output voltage of the multi-
plier is forced to decrease, thus reducing the energy
drawn from the mains. If the current exceeds 40
µ
A,
the OVP protection is triggered (Dynamic OVP), and
the external power transistor is switched off until the
current falls approximately below 10µA.
However, if the overvoltage persists, an internal
comparator (Static OVP) confirms the OVP condi-
tion keeping the external power switch turned off
(see fig. 1).
Finally, the overvoltage that triggers the OVP
function is:
∆
Vout = R
1
⋅
40
µ
A.
Typical values for R
1
, R
2
and C are shown in the
application circuits. The overvoltage can be set inde-
pendently from the average output voltage. The pre-
cision in setting the overvoltage threshold is 7% of
STMICROELECTRONICS [ STMICROELECTRONICS ]
