MP8903 – LOW DROPOUT, 150mA LINEAR REGULATOR
MP8903 Rev. 1.11 www.MonolithicPower.com 6
4/30/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2015 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 100k in
order to minimize the impact of the internal
resistor divider. For an accurate output-voltage
setting, use 10k (±1%) for the low-side
resistor R2 of the voltage divider, while the
high-side resistor R1 can be determined by the
equation:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
×=
FB
FBOUT
V
VV
2R1R
Where V
FB
is the OUT feedback threshold
voltage equal to 1.222V.
Example: For 2.5V Output
Ω=
⎟
⎠
⎞
⎜
⎝
⎛
Ω
−
= k41.10
k10
V222.1
V222.1V5.2
1R
You can select a standard 10.5k (±1%)
resistor for R1.
The following table lists the selected R1 values
for some typical output voltages:
Table 1—Adjustable Output Voltage R1 Values
V
OUT
(V) R1 (Ω)
R2 (Ω)
1.25 232
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
10k
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.
