MP8903 – LOW DROPOUT, 150mA LINEAR REGULATOR

MP8903 Rev. 1.11

www.MonolithicPower.com

6

4/4/2011

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© 2011 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output Voltage

The fixed output voltage of the MP8903 is set to

2.5V, 2.85V or 3.3V, depending on the internal

resistor divider (Figure 1). You can also adjust

the output voltage by using an external resistor

divider (R1 and R2 in Figure 2). However, the

sum of R1 and R2 should not exceed 100kΩ in

order to minimize the impact of the internal

resistor divider. For an accurate output-voltage

setting, use 10kΩ (

±1%) for the low-side

resistor R2 of the voltage divider, while the

high-side resistor R1 can be determined by the

equation:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

×

=

FB

FB

OUT

V

V

V

2

R

1

R

voltage equal to 1.222V.

Example: For 2.5V Output

Ω

=

⎟

⎠

⎞

⎜

⎝

⎛

Ω

−

=

k

41

.

10

k

10

V

222

.

1

V

222

.

1

V

5

.

2

1

R

You can select a standard 10.5kΩ (

±1%)

resistor for R1.

The following table lists the selected R1 values

for some typical output voltages:

Table 1—Adjustable Output Voltage R1 Values

R1 (Ω)

R2 (Ω)

1.25

232

10k

1.5

2.26k

1.8

4.75k

2

6.34k

2.5

10.5k

2.8

13k

3

14.7k

3.3

16.9k

4

22.6k

5

30.9k

In Figures 3 and 4, C2 is added for an improved

transient response.

Input Capacitor Selection

For proper operation, place a ceramic capacitor

(C1) between 1µF and 10µF of dielectric type

X5R or X7R between the input pin and ground.

Larger values in this range will help improve

line transient response at the drawback of

increased size.

Output Capacitor Selection

For stable operation, use a ceramic capacitor

(C3) of type X5R or X7R between 1µF and

10µF. Larger values in this range will help

improve load transient response and reduce

noise with the drawback of increased size.

Output capacitors of other dielectric types may

be used, but are not recommended as their

capacitance can deviate greatly from their rated

value over temperature.

To improve load transient response, add a

small ceramic (X5R, X7R or Y5V dielectric)

100nF feed forward capacitor in parallel with

R1. The feed forward capacitor is not required

for stable operation.