MP103 Rev. 1.01

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14

1/23/2014

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APPLICATION INFROMATION

COMPONENT SELECTION

Setting the Output Voltage

The output voltage is set to 12V by internal large

feedback resistors. Typically, the internal upper

and lower feedback resistor is 1.125MΩ and

125kΩ respectively. Adjust VOUT by choosing

appropriate external feedback resistors. The

recommended output voltage is between 1.5V

and 15V. Defining the upper and lower feedback

picture in Typical Application section):

=×

−

UP

LW

VOUT

RR

(

1)

1.235

For the external resistors to dominate over the

internal resistors, select relatively small values of

However, to minimize the load consumption,

avoid very small external resistors. For most

counter the internal upper-feedback resistor

value of 1.125MΩ typically. The table below lists

typical resistor values for different output

voltages.

Table 1: Resistors Selecting vs. Output

Voltage Setting

VOUT (V)

1.5

2.21 (1%)

10.2 (1%)

3.3

16.9 (1%)

10.2 (1%)

5

30.9 (1%)

10.2 (1%)

15

121 (1%)

10.2 (1%)

Selection of VB Capacitor

The bypass capacitor on the VB pin needs to be

sufficiently large to support sufficient energy.

Calculate the capacitance (in μF) based on the

following equation:

×τ

s

VB

ripple

I

C

V

s

based on the type of input rectifier—for example,

s

the VB capacitor—normally the ripple is limited to

2V to 3V. For best results, use a small ceramic

capacitor and a large aluminum capacitor in

parallel.

Output Power Capability

The following factors influence the MP103’s

maximum output power: the input rectifier (full

bridge or half-wave); the VB capacitor connected

between VB and GND; the DC current gain and

collector current of external BJT; the output

voltage and the temperature-rise requirement of

key components, which is relevant to different

application environments.

GND

GND

Full Bridge Rectifier

Half-wave Rectifier

Figure 5 depicts the relationship between the

maximum output power and the VIN voltage

when the output voltage is 12V, 5V and 3.3V

respectively. The plots account for the full bridge

rectifiers, the temperature rise of MP103 is less

temperature test.

0

200

400

600

800

1000

1200

1400

85 115 145 175 205 235 265 295

Figure 5: Output Power vs. Input Voltage