MP100 – OFFLINE INDUCTOR-LESS REGULATOR
MP100 Rev. 1.04 www.MonolithicPower.com 10
1/23/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2014 MPS. All Rights Reserved.
The maximum output capability can be roughly
estimated by following equation:
×××× − ×
=
+×π×××
VD peak line THVIN DMIN o
o_max
peak vd in line
2C I f (V V )V
P
I22CVf
Where,
VD
C
( F) is the capacitance connected to VD;
peak
I
(A) is the input peak current at full load,
which can be estimated by following equation:
=− ×
peak DMIN
I 1.25 0.036 V
;
line
f
(Hz) is the rectified line frequency;
THVIN
V
(V) is the input voltage threshold to shut
down the internal switch connected between VIN
and VB, typically it is 35V;
DMIN
V
(V) is the minimum voltage of VD to
maintain the output voltage, usually; it can be got
by following equation:
+>
⎧
=
⎨
≤
⎩
oDMIN
DMIN
DMIN
V1ifV 6.8V
V
6.8V if V 6.8V
o
V
(V) is the output voltage;
in
V
(V) is the RMS value of input voltage;
To get more output power, MP100 can be
paralleled. Figure 6 shows how it is implemented.
More MP100 can be paralleled in the same way
to get the output power need.
Another way to get more output power is using
an external MOSFET to charge the capacitor
connected between VD and GND. Figure 7
shows an example. To prevent the thermal
damage of external MOS when VD is shorted to
GND directly, PTC (Positive Temperature
Coefficient) is used which should be placed as
close as to the external MOS to detect the
temperature. When the temperature of external
MOS reaches certain value, the resistor of PTC
will increase sharply to pull down the gate
voltage and shut down the external MOS. To
guarantee its normal start up and steady state
operation, R3/R2 should be more than 4.5. At the
same time, R3/R2 should not be too high to get
better thermal protection; generally it should be
less than 10. R1 can be used to adjust the switch
speed of external MOS.
Line Transformer
MP100 can work well when connected to AC line
or programmable AC source. But when using an
isolation transformer or a variable transformer as
source, because of the high inductance of the
transformer (usually in the mH’s), high voltage
spikes occur when MP100 turns off the internal
switch connected between VIN and VB, which
may damage the IC. An X- capacitor must be
installed before the rectifier to guarantee the
reliability of the system.
EMI
An appropriate X-capacitor should be connected
between the input ports to guarantee the circuit
can meet EMI requirements. Figure 3 shows the
recommended X-capacitor values to pass EMI in
different applications.
0.22
0.22
0.47
0.68
1
0.22 0.22
0.22
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 5 10 15 20 25
0
0.2
0.4
0.6
0.8
1
0 2.5 5 7.5 10 12.5
0.22
0.22
0.22
0.22
0.22
0.33
0.22
0.47
Figure 3: X Cap Value Required in Different
Application
