L4984D STMicroelectronics, L4984D Datasheet - Page 26

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

Specifications of L4984D

• Rohs: yes

Soft-start
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Soft-start
To reduce inrush energy at startup or after an auto-restart protection tripping, the L4984
uses soft-start. Please refer to
housekeeping functions
The function is performed by internally pulling the voltage on the MULT pin towards an
asymptotic level located at about 4.1 V as the device wakes up. This has a twofold effect: on
the one hand, the output of the multiplier is lowered through the voltage feedforward
function, therefore programming a lower peak current; on the other hand, the off-time of the
power switch is considerably prolonged with respect to the normal values programmed by
the capacitor connected to the TIMER pin. In this way, both the current inrush and the risk of
saturating the boost inductor at startup are minimized.
After 300 μs from its activation, the pull-up is released. The voltage on the MULT pin decays
with the time constant determined by the resistor divider that biases the pin and the bypass
capacitor typically connected between the pin and ground to reduce noise pick-up. At the
same time, C
(see
The soft-start function is performed at turn-on by VCC Turn-on threshold (V
brownout function and at startup by PFC_OK. On the following activations by PFC_OK (like
during burst-mode operation driven by a D2D converter controller) the soft-start function is
not performed.
soft-start function.
Figure 33. Startup mechanisms and activations of the soft-start function
Section 8: Voltage feedforward
FF
Figure 33
is discharged by turning on the internal low impedance discharge switch
for more details of the events triggering soft-start.
shows the different startup mechanisms and the activations of the
Doc ID 023489 Rev 3
Table 1
).
in
Section 12: Power management and
CCOn
), by the
L4984