MP100 – OFFLINE INDUCTOR-LESS REGULATOR

MP100 Rev. 1.04

www.MonolithicPower.com

10

1/23/2014

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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

I2 2

C

V

f

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

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

V1

if V

6.8V

V

6.8V

if V

6.8V

o

in

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