MP2005 – 800mA, HIGH PSRR,ULDO LINEAR REGULATOR

MP2005 Rev. 0.92

www.MonolithicPower.com

8

5/5/2010

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APPLICATION INFORMATION

Setting the Output Voltage

The MP2005 has an adjustable output voltage,

set by using a resistive voltage divider from the

output voltage to FB pin. The voltage divider

divides the output voltage down to the feedback

voltage by the ratio:

2

R

1

R

2

R

V

V

OUT

FB

+

=

Thus the output voltage is:

2

R

2

R

1

R

5

.

0

+

×

=

R2 can be as high as 100kΩ, but a typical value

is 10kΩ. Using that value, R1 is determined by:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

×

=

FB

FB

OUT

V

V

V

2

R

1

R

For example, for a 1.8V output voltage, R2 is

10kΩ, and R1 is 26kΩ. You can select a

standard 26kΩ (±1%) resistor for R1.

The following table lists the selected R1 for

various output voltages.

Table 1—Adjustable Output Voltages R1 Values

R1 (kΩ)

R2 (kΩ)

1.25

15

1.5

20

1.8

26

2

30

2.5

40

2.8

46

3

50

3.3

56

4

70

10

Bias Input

The bias input is designed for low drop

application. The bias pin must be at least 2.7V,

supply voltage meets these requirements, the

Feed Forward Capacitor

For stability, it needs a 10nF capacitor parallel

with R1. The ceramic type capacitor, will

provide the best performance.