L4984D STMicroelectronics, L4984D Datasheet - Page 17

• Manufacturer Part Number: L4984D
• Description: Power Factor Correction ICs Current Mode PFC CCM Line Modulated Bi
• Manufacturer: STMicroelectronics

Specifications of L4984D

• Rohs: yes

L4984
Figure 26. Line-modulated fixed-off-time modulator: a) internal block diagram; b)
With reference to the schematic and the relevant key waveforms in
proportional to the instantaneous line voltage is achieved by charging the capacitor CT with
a constant current ITIMER, accurately fixed internally and temperature compensated, while
the MOSFET is off and commanding MOSFET turn-on (and resetting CT at zero) as the
voltage across CT equals that on the MULT pin. The voltage on this pin is:
Equation 5
where KP is the divider ratio of the resistors biasing the MULT pin. As a result:
Equation 6
and the switching frequency is:
Equation 7
The timing capacitor CT, therefore, is selected with the following design formula:
Equation 8
V
within the multiplier linearity range (0 to 3 V) and ITIMER is specified in
characteristics
out
C
and fsw are design specifications, K
T
TIMER
I
COMP
Timer
key waveforms
.
MULT
T
OFF
OFF
+
-
a)
0
ON
=
Multiplier
f
sw
I
TIMER
C
Doc ID 023489 Rev 3
=
PWM Latch
S
R
T
T
Q
1
sw
CS
V
K
+
-
MULT
C =
P
Comparator
=
Vpk
T
PWM
K
Driver
P
=
P
is chosen so that the voltage on the MULT pin is
K
I
C
K
sinθ
TIMER
P
P
T
I
GD
Vout
TIMER
Vpk
Vout
→
sin
f
sw
=
TIMER
GD
CS
θ
K
K
R
Q
S
t
t
Vout
T
1
OFF
=
I
TIMER
C
T
ON
MULT
T
Application information
Figure 26
Multiplier output
K
b)
P
Section 3: Electrical
, an off-time
AM13242v1
17/35
t
t
t
t
t
t