L4984D STMicroelectronics, L4984D Datasheet - Page 30

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

Specifications of L4984D

• Rohs: yes

Power management and housekeeping functions
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Power management and housekeeping functions
A communication line with the control IC of the cascaded DC-DC converter can be
established via the disable function included in the PFC_OK pin (see
failure detection (FFD)
controller of the cascaded DC-DC converter to shut down the L4984 in case of light load and
to minimize the no-load input consumption. Should the residual consumption of the chip be
an issue, it is also possible to cut down the supply voltage. Interface circuits like those are
shown in
converter stage works as the master and the PFC stage as the slave or, in other words, that
the DC-DC stage starts first; it powers both controllers and enables/disables the operation of
the PFC stage.
Figure 37. Interface circuits that let DC-DC converter controller IC disable the L4984
Another available function is brownout protection, which is basically a not-latched shutdown
function that is activated when a condition of mains undervoltage is detected. This condition
may cause overheating of the primary power section due to an excess of RMS current.
Brownout can also cause the PFC pre-regulator to work in open loop, which may be
dangerous to the PFC stage itself and the downstream converter, should the input voltage
return abruptly to its rated value. Another problem is the spurious restarts that may occur
during converter power-down and that cause the output voltage of the converter to not
decay to zero monotonically. For these reasons it is usually preferable to shut down the unit
in the case of brownout. The brownout threshold is internally fixed at 0.8 V and is sensed on
the VFF pin while the voltage is falling. An 80 mV hysteresis prevents rebounding at input
voltage turn-off.
The soft-start function is performed by PFC_OK enable threshold (V
startup, but not on the following activations, to ensure a proper burst-mode operation (as
described in
ON/OFF control.
In
that cause the device to stop operating.
Table 6
Figure 37
it is possible to find a summary of all of the above mentioned working conditions
Figure 33
. Needless to say, this operation assumes that the cascaded DC-DC
). For this reason pin MULT is suggested to be used as remote
for more details). Typically this line is used to allow the PWM
V
CC
5
Doc ID 023489 Rev 3
L6599A
L6591
L6566A
8
9
6
PFC_STOP
PFC_STOP
V
CC
_PFC
PFC_OK
PFC_OK
V
CC
6
6
10
L4984
L4984
L4984
PFC_OK_E
Section 7: Feedback
) only at
AM13252v1
L4984