MP20045 – LOWER NOISE, 1A LINEAR REGULATOR

MP20045 Rev. 1.0

www.MonolithicPower.com

11

10/13/2010

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© 2010 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output Voltage

The output voltage of MP20045 can be set

externally which ranges from 1.5V to 5V by

operating from +2.5V to +5.5V input or preset

internally at 1.5V, 1.8V, 2.5V, 3.3V, 5V. For the

adjustable version, the output voltage is 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:

R2

R2

R1

1.5

+

×

=

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 2.8V output voltage, R2 is

10kΩ, and R1 is 8.66kΩ. You can select a

standard 8.66kΩ (±1%) resistor for R1.

Power Dissipation

The power dissipation for any package depends

on the thermal resistance of the case and circuit

board, the temperature difference between the

junction and ambient air, and the rate of air flow.

The power dissipation across the device can be

represented by the equation:

()

OUT

OUT

IN

I

V

V

P

×

−

=

The allowable power dissipation can be

calculated using the following equation:

()

JA

Ambient

Junction

(MAX)

T

T

P

θ

−

=

/

difference between the junction and the

resistance from the junction to the ambient

environment. Connecting the GND pin of

MP20045 to ground using a large pad or

ground plane helps to channel heat away.

Output Capacitor Selection

The MP20045 is designed specifically to work

with very low ESR ceramic output capacitor in

space-saving and performance consideration. A

2.2µF ceramic capacitor with ESR lower than

0.9Ω is suitable for the MP20045 application

circuit. Output capacitor of larger values will

help to improve load transient response and

reduce noise with the drawback of increased

size.

0.1

1

10

100

0

100

200

300

400

500

600

700

800

900 1000

OUTPUT CURRENT(mA)

Figure 2—Relationship between ESR and

LDO Stability