MP20045 – LOWER NOISE, 1A LINEAR REGULATOR
APPLICATION INFORMATION
Setting the Output Voltage
Output Capacitor Selection
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:
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
0.9ꢀ 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.
100
10
1
R2
VFB = VOUT
R1+ R2
Where VFB is the feedback threshold voltage
(VFB = 1.5V), and VOUT is the output voltage.
Thus the output voltage is:
R1+R2
R2
VOUT = 1.5×
R2 can be as high as 100kΩ, but a typical value
is 10kΩ. Using that value, R1 is determined by:
0.1
0
100 200 300 400 500 600 700 800 900 1000
OUTPUT CURRENT(mA)
⎛
⎜
⎜
⎞
⎟
⎟
VOUT − VFB
R1 = R2×
Figure 2—Relationship between ESR and
LDO Stability
VFB
⎝
⎠
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:
P =
(
V
IN − VOUT ×IOUT
)
The allowable power dissipation can be
calculated using the following equation:
P
=
(
TJunction − TAmbient / θJA
)
(MAX)
Where (TJunction − TAmbient) is the temperature
difference between the junction and the
surrounding environment, θJA is the thermal
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.
MP20045 Rev. 1.0
10/13/2010
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
11
MPS [ MONOLITHIC POWER SYSTEMS ]
