MP163 – 700V, NON-ISOLATED, OFFLINE REGULATOR WITH INTEGRATED LDO
OPERATION
The MP163 is a green-mode operation
regulator. The peak current and the switching
frequency both decrease with a decreasing load.
As a result, the MP163 offers excellent light-
load efficiency and improves overall average
efficiency. The regulator also incorporates
multiple features and operates with a minimum
number of external components.
Figure 2: Minimum Off Time at Start-Up
Constant Voltage (CV) Operation
The MP163 regulates the output voltage by
monitoring the sampling capacitor (C3).
The MP163 acts as a fully integrated regulator
when used in a buck topology (see the Typical
Application on page 2).
At the beginning of each cycle, the integrated
MOSFET turns on while the feedback voltage
drops below the 2.55V reference voltage, which
indicates an insufficient output voltage. The
peak current limitation determines the on period.
After the on period elapses, the integrated
MOSFET turns off. The sampling capacitor (C3)
voltage is charged to the output voltage through
D3 when the freewheeling diode (D2) turns on.
This way, the sampling capacitor (C3) samples
and holds the output voltage for output
regulation. The sampling capacitor (C3) voltage
decreases when the inductor (L1) current falls
below the output current. When the feedback
voltage falls below the 2.55V reference voltage,
a new switching cycle begins. Figure 3 shows
this operation in continuous conduction mode
(CCM).
Start-Up and Under-Voltage Lockout (UVLO)
The internal high-voltage regulator self-supplies
the IC from DRAIN. When VCC reaches
VCCOFF, the IC starts switching, and the internal
high-voltage regulator turns off. The internal
high-voltage regulator turns on to charge the
external VCC capacitor when VCC falls below
VCCON. A small capacitor (in the low μF range)
maintains VCC and lowers the capacitor cost.
The IC stops switching when VCC drops below
VCCstop
.
Under fault conditions (such as OLP, SCP, and
TSD) the IC stops switching, and an internal
current source (~16μA) discharges the VCC
capacitor. The internal high-voltage regulator
will not charge the VCC capacitor until VCC
drops below VCCpro. The restart time can be
estimated using Equation (1):
MOSFET
Diode
VCC VCCpro VCCOFF VCC
(1)
pro
T
CVCC
restart
ICCLATCH
Iregulator
IL
Ipeak
Io
Soft Start (SS)
Vo
The IC stops operation when VCC drops below
VCCstop. The IC begins operation when VCC
charges to VCCOFF. There is a soft-start
period whenever the chip starts operation.
Soft start prevents the inductor current from
overshooting by limiting the minimum off time.
VFB
2.55V
Figure 3: VFB vs. VO
Determine the output voltage with Equation
(2):
The MP163 adopts a two-phase minimum off-
time limit soft start. Each soft-start phase lasts
for 128 switching cycles. During soft start, the
off-time limit shortens gradually from τminoff_SS1
to τminoff_SS2 and reaches τminoff (see Figure 2).
R1 R2
(2)
Vo 2.55V
R2
MP163 Rev. 1.01
8/11/2017
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