MP2149 –6V, 1A, LOW QUIESCENT CURRENT, DUAL, SYNC BUCK REGULATOR
MP2149 Rev.1.01 www.MonolithicPower.com 11
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• Switching Loss (SW)
• MOSFET Driver Current (DR)
• Supply Current (S)
Based on these parameters, we can estimate the
power loss as:
LOSS Cond DT SW DR S
PPPPPP=++++
Thermal Regulation
As previously discussed, changes in IC
temperature change the electrical characteristics,
especially when the temperature exceeds the
IC’s recommended operating range. Managing
the IC’s temperature requires additional
considerations to ensure that the IC runs below
the maximum-allowable temperature. While
operating the IC within recommended electrical
limits is a major component to maintaining proper
thermal regulation, specific layout designs can
improve the thermal profile while limiting costs to
either efficiency or operating range.
For the MP2149, connect the ground pin on the
package to a GND plane on top of the PCB to
use this plane as a heat sink. Connect this GND
plane to GND planes beneath the IC using vias
to further improve heat dissipation. However,
given that these GND planes can introduce
unwanted EMI noise and occupy valuable PCB
space, design the size and shape of these planes
to match the thermal resistance requirement:
SA JA JC
θ=θ−θ
However, connecting the GND pin to a heat sink
can not guarantee that the IC will not exceed its
recommended temperature limits; for instance, if
the ambient temperature exceeds the IC’s
temperature limits. If the ambient air temperature
approaches the IC’s temperature limit, options
such as derating the IC so it operates using less
power can help prevent thermal damage and
unwanted electrical characteristics.
PCB Layout
Proper layout of the switching power supplies is
very important, and sometimes critical for proper
function: poor layout design can result in poor
line or load regulation and stability issues.
Place the high-current paths (GND, IN and SW)
very close to the device with short, direct, and
wide traces. Place the input capacitor as close as
possible to the IN and GND pins. Place the
external feedback resistors next to the FB pin.
Keep the switching node SW short and away
from the feedback network. The circuit of below
PCB layout is shown in Figure 4.
1
8
7
6
5
OUT1
EN2
SW1
VIN
C1A C1B
R1
R2
AGND
SW2
OUT2
EN1
R3
R4
C3
C4
C6
C5
GND
2
3
4
Figure 3: Suggested PCB Layout
Design Example
Below is a design example following the
application guidelines for the specifications:
Table 3: Design Example
VIN
5V
VOUT1
1.8V
VOUT2
1.2V
The detailed application schematic is shown in
Figure 1. The typical performance and circuit
waveforms have been shown in the Typical
Performance Characteristics section. For more
device applications, please refer to the related
Evaluation Board Datasheets.
