MPS MP150 - Operation

MP150 – OFFLINE PRIMARY-SIDE REGULATOR
MP150 Rev. 1.14 www.MonolithicPower.com 9
9/25/2018 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2018 MPS. All Rights Reserved.
OPERATION
The MP150 is a green-mode-operation regulator.
The peak current and the switching frequency
both decrease as the load decreases to provide
excellent efficiency at light load, and thus
improve the overall average efficiency. The
typical application diagram shows that the
regulator operates using a minimal number of
external components. It incorporates the
following features:
Start-up and Under Voltage Lock-out
The internal high-voltage regulator supplies the
IC from the Drain pin. The IC starts switching and
the internal high voltage regulator turns off when
the voltage on VCC reaches 5.6V. When the
VCC voltage drops below 5.3V, the internal high
voltage regulator turns on again to charge the
external VCC capacitor. Use a capacitor in the
several µF range stabilize the VCC voltage and
this can lower the cost by decreasing the value of
the capacitor.
When the voltage on VCC drops blow 3.4V, the
IC stops, then the internal high-voltage regulator
charges the VCC capacitor.
When faults occur, such as overload, short circuit,
and over-heating, the IC stops working and an
internal current source (16µA) discharges the VCC
capacitor. Before the VCC voltage drops below
2.4V, the internal high-voltage regulator remains off
and the VCC capacitor remains discharged.
Estimate the restart time after a fault as:
CC
restart VCC VCC
V2.4V
5.6V 2.4V
tC C
16uA 3.5mA


 
Figure 2 shows the typical waveform with VCC
under-voltage lockout.
V
CCH
=5.6V
V
CCL
=5.3V
V
CC
Internal
Current
Source
Driving
Signal
ON
OFF
V
CCStop
=3.4V
Figure 2: VCC Under-Voltage Lockout
Constant Voltage Operation
The MP150 is a fully-integrated regulator when
used in a Buck solution as shown in the typical
application on page 1.
The integrated MOSFET turns ON at the
beginning of each cycle when the feedback
voltage is below the reference voltage (2.5V),
which indicates insufficient output voltage. The
peak current limit determines the ON period.
After the ON period elapses, the integrated
MOSFET turns OFF. The freewheeling diode (D1)
remains OFF until the inductor current charges
the sampling capacitor (C3) voltage to the output
voltage level. Then the sampling capacitor
voltage changes with the output voltage. The
sampling capacitor can sample and hold the
output voltage to regulate the output voltage. The
sampling capacitor voltage decreases after the
inductor current drops below the output current.
When the feedback voltage falls below the
reference voltage (2.5V), a new switching cycle
begins.
Figure 3 shows the detailed operation timing
diagram under CCM.