MP44014-A – BOUNDARY MODE PFC CONTROLLER
MP44014-A Rev. 1.01 www.MonolithicPower.com 11
11/10/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2015 MPS. All Rights Reserved.
OPERATION
The MP44014-A is a boundary conduction mode
PFC controller that is optimized for the PFC pre-
regulator up to 300W and fully complies with the
IEC1000-3-2 specification.
Output-Voltage Regulation
The output voltage is sensed at FB through a
resistor divider from the output voltage to ground.
The on-chip reference voltage and the high-
performance error amplifier regulate the output
voltage accurately.
Over-Voltage Protection (OVP)
The MP44014-A offers two stages of over-
voltage protection: dynamic over-voltage
protection and static over-voltage protection.
With two-stage protection, the circuit operates
reliably.
The MP44014-A achieves OVP by monitoring the
current flow through COMP.
During steady-state operation, the current flow
through the high-side feedback resistor (R9) and
the low-side feedback resistor (R10) is:
OFB
FB
R9 R10
VV
V
II
R9 R10
If there is an abrupt rise on the output (ΔV
O
), the
compensation network connected between FB
and COMP takes time to achieve a high-power
factor (PF), due to the long RC time constant.
The voltage on FB will still be kept at the
reference value. The current through R10
remains equal to V
FB
/R10, but the current through
R9 will become:
'
OOFB
R9
VVV
I
R9
This current has to flow into COMP. At the same
time, this current is monitored inside the chip. If
the current rises to 25µA, the output voltage of
the multiplier will be forced to decrease, and the
energy delivering to output will be reduced. If this
current continues to rise (to about 27µA), the
dynamic OVP could be triggered. Consequently,
the gate driver is blocked to turn off the external
power MOSFET, and the device enters an idle
state. This state is maintained until the current
falls below 10µA, the point at which the internal
starter will be re-enabled and allow the switching
to re-start.
When the load is very light, the output voltage
tends to stay steadily above the nominal value. In
this condition, the error amplifier output will
saturate low. When the error amplifier output is
lower than 2.25V, the static OVP is triggered.
Consequently, the gate driver is blocked to turn
off the external power MOSFET, and the device
enters an idle state. Normal operation resumes
once the error amplifier output goes back into the
regulated region (see Fig. 2).
2.5V
+
-
FB
COMPMULT
UVLO
GATE
Multiplier
Over-Voltage
Detection
Driver
Vo
R9
R10
I
R9
I
R10
FIGURE 2. OVP Detector Block
Disable/Enable or OLP Function
The MP44014-A can be disabled by pulling FB
lower than 200mV. This helps reduce quiescent
current when the PFC pre-regulator needs to
shut down. To enable the IC, the voltage on FB
must exceed 0.45V. This function is used mainly
as a remote on/off control input that is driven by a
PWM controller for power management purposes.
Also, FB acts as an open-loop protection for
safety purposes. The IC shuts off PWM if the
lower resistor of the output divider is shorted to
ground or if the upper resistor is missing or fails
to open.
Boundary Conduction Mode
When the current of the boost inductor reaches
zero, the voltage on the inductor is reversed.
Then ZCS generates the turn-on signal of the
MOSFET by sensing the falling edge of the
voltage on the auxiliary winding coupled with the
inductor. If the voltage of ZCS rises above 1.4V,
the comparator waits until the voltage falls
