STMicroelectronics 19V - 90W Adapter with PFC for Laptop computers using the L6563H and L6699 EVL6699-90WADP EVL6699-90WADP Fiche De Données
Codes de produits
EVL6699-90WADP
Line sensing function
L6699
30/38
Doc ID 022835 Rev 2
10
Line sensing function
This function basically stops the IC as the input voltage to the converter falls below the
specified range and lets it restart as the voltage goes back within the range. The sensed
voltage can be either the rectified and filtered mains voltage, in which case the function acts
as a brownout protection, or, in systems with a PFC pre-regulator front-end, the output
voltage of the PFC stage, in which case the function serves as a power-on and power-off
sequencing.
specified range and lets it restart as the voltage goes back within the range. The sensed
voltage can be either the rectified and filtered mains voltage, in which case the function acts
as a brownout protection, or, in systems with a PFC pre-regulator front-end, the output
voltage of the PFC stage, in which case the function serves as a power-on and power-off
sequencing.
L6699 shutdown upon input undervoltage is accomplished by means of an internal
comparator, as shown in the block diagram of
comparator, as shown in the block diagram of
, whose non-inverting input is
available at pin 7 (LINE). The comparator is internally referenced to 1.22 V and disables the
IC if the voltage applied at the LINE pin is below the internal reference. Under these
conditions the soft-start is discharged, the PFC_STOP pin is open and the consumption of
the IC is reduced. PWM operation is re-enabled as the voltage on the pin is above the
reference. The comparator is provided with current hysteresis instead of a more usual
voltage hysteresis: an internal 13 µA current sink is ON as long as the voltage applied at the
LINE pin is below the reference and is OFF if the voltage is above the reference.
IC if the voltage applied at the LINE pin is below the internal reference. Under these
conditions the soft-start is discharged, the PFC_STOP pin is open and the consumption of
the IC is reduced. PWM operation is re-enabled as the voltage on the pin is above the
reference. The comparator is provided with current hysteresis instead of a more usual
voltage hysteresis: an internal 13 µA current sink is ON as long as the voltage applied at the
LINE pin is below the reference and is OFF if the voltage is above the reference.
This approach provides an additional degree of freedom: it is possible to set the ON
threshold and the OFF threshold separately by properly choosing the resistors of the
external divider (see below). With voltage hysteresis, on the other hand, fixing one threshold
automatically fixes the other one depending on the built-in hysteresis of the comparator.
threshold and the OFF threshold separately by properly choosing the resistors of the
external divider (see below). With voltage hysteresis, on the other hand, fixing one threshold
automatically fixes the other one depending on the built-in hysteresis of the comparator.
, the following relationships can be established for the ON
(Vin
ON
) and OFF (Vin
OFF
) thresholds of the input voltage:
Equation 12
which, solved for R
H
and R
L
, yields:
Equation 13
L
H
OFF
L
6
H
O N
R
25
.
1
=
R
25
.
1
Vin
;
R
25
.
1
+
10
·
13
=
R
25
.
1
Vin
-
-
-
25
.
1
Vin
25
.
1
R
=
R
;
10
·
13
Vin
Vin
=
R
OFF
H
L
6
OFF
ON
H
-
-