L4984D STMicroelectronics, L4984D Datasheet - Page 22

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

Specifications of L4984D

• Rohs: yes

Feedback failure detection (FFD)
7
22/35
Feedback failure detection (FFD)
The OVP function handles “normal” overvoltage conditions, i.e. those resulting from an
abrupt load/line change or occurring at startup. If the overvoltage is generated by a
feedback failure, for instance when the upper resistor of the output divider (R1) fails open,
eventually the error amplifier output (COMP) saturates high and the voltage on its inverting
input (INV) drops from its steady-sate value (2.5 V). An additional comparator monitors the
voltage on the INV pin, comparing it against a reference located at 1.66 V. When the voltage
on pin PFC_OK exceeds 2.5 V and, simultaneously, that on the INV pin falls below 1.66 V,
the FFD function is triggered: the gate drive activity is immediately stopped, the device is
shut down and its quiescent consumption reduced. This condition is latched and to restart
the IC it is necessary to recycle the input power, so that the V
The pin PFC_OK doubles its function as a not-latched IC disable: a voltage below 0.23 V
shuts down the IC, reducing its consumption below 2 mA. To restart, simply let the voltage
on the pin go above 0.27 V. Note that these functions offer complete protection against not
only feedback loop failures or erroneous settings, but also against a failure of the protection
itself. Either resistor of the PFC_OK divider failing short or open or a pin PFC_OK floating
results in shutting down the IC and stopping the pre-regulator.
Doc ID 023489 Rev 3
CC
voltage goes below 6 V.
L4984