MP20048 – CAPACITOR-FREE, 250mA, LOW DROPOUT VOLTAGE REGULATOR

MP20048 Rev. 0.91

www.MonolithicPower.com

9

4/6/2010

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© 2010 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output Voltage

The output voltage of MP20048 can get any

value of output between 1.234V to 5V. 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

1.234

+

×

=

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 2.5V output voltage, R2 is

10kΩ, and R1 is 10.2kΩ. You can select a

standard 10.2kΩ (±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.

Output Capacitor Selection

The MP20048 does not require the output

capacitor for stable operation. It is specifically

designed to be stable with any type and value

capacitor including ceramic and electrolytic.

Although an output capacitor is not required for

stability, the output capacitor, C2, is optional to

be connected at the output side. (Figure 2)

Output capacitor of larger values will help to

improve load transient response and reduce

output noise with the drawback of increasing

size.

Output Noise

A precision bandgap reference is used to

generate the internal reference voltage, VREF,

which is the dominant noise source within the

MP20048. It is optional to connect a feed

forward capacitor, C3, from the output to

feedback to improve load transient performance.

This capacitor, C3, should be limited to be less

than 0.1uF. (Figure 2)

IN

EN

(

optional)

(

optional)

OUT

FB

GND

VIN

C1

R1

R2

C3

C2

VOUT

MP20048

Figure2. Typical Application Circuit with

optional output cap and feedforward cap