MP158 –SMALL, ENERGY-EFFICIENT, OFF-LINE REGULATOR

MP158 Rev. 1.0

www.MonolithicPower.com

14

10/17/2014

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So, when reducing dummy load to achieve

30mW no load requirement, no load regulation

will get worse.

Use a zener to reduce no-load consumption if no-

load regulation is not a concern.

Auxiliary VCC Supply

achieve the 30mW no-load power requirement. In

order to do this, chip requires an external VCC

supply to reduce overall power consumption.

This auxiliary VCC supply is derived from the

resistor connected between C3 and C4. C4

should be set larger than recommendation above.

D3 is used in case that VCC interfere with FB, R3

is determined per the formula below.

o

S

V5.8V

R

I

−

≈

 

condition. R should be adjusted to meet the

about 180uA.

Surge Performance

Select an appropriate input capacitor value to

obtain a good surge performance. Figure 9

shows the half-wave rectifier. Table 2 shows the

capacitance required under normal condition for

different surge voltages. In this test, FR1 is

20Ω/2W fused resistor and L1 is 1mH.

Figure 9: Half-Wave Rectifier

Table 2: Recommended Capacitance

Surge voltage

500V

1000V

2000V

C1

1μF

10μF

22μF

C2

1μF

4.7μF

10μF

Layout Guide

PCB layout is very important for reliable

operation, good EMI and thermal performance.

Please follow these guidelines to optimize

performance.

1) Minimize the loop area formed by the input

capacitor, IC, freewheeling diode, inductor

and output capacitor.

2) Place the power inductor far away from the

input filter while keeping the loop area to the

inductor to a minimum, see example below.

3) Place a capacitor valued at several hundred

pF between the FB pin and source as close

the IC as possible.

4) Connect exposed pads or larger copper area

with the DRAIN pin to improve thermal

performance.