AAT1149B Datasheet, PDF (11/17 Pages) Advanced Analogic Technologies – 2.2MHz Fast Transient 400mA Step-Down Converter

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PRODUCT DATASHEET
AAT1149B
2.2MHz Fast Transient 400mA Step-Down Converter
Figure 1: AAT1149BIUV Evaluation Board
Top Side.
Figure 2: AAT1149BIUV Evaluation Board
Bottom Side.
V_IN
U1
L1
4
5
IN
LX
EN
AAT1149BIUV
C3
open
2
EN
1
FB
C2
4.7μF
3
GND
R1
0
R2
open
V_OUT
C1
4.7μF
WLCSP-5
Figure 3: AAT1149BIUV Evaluation Board Schematic.
Thermal Calculations
There are three types of losses associated with the
AAT1149B step-down converter: switching losses, con-
duction losses, and quiescent current losses. Conduction
losses are associated with the R_DS(ON) characteristics of
the power output switching devices. Switching losses are
dominated by the gate charge of the power output
switching devices. At full load, assuming continuous con-
duction mode (CCM), a simplified form of the losses is
given by:
P_TOTAL =
I_O2 · (R_DS(ON)H · V_O + R_DS(ON)L · [V_IN - V_O])
V_IN
+ (t_sw · F_S · I_O + I_Q) · V_IN
I_Q is the step-down converter quiescent current. The
term t_sw is used to estimate the full load step-down con-
verter switching losses.
1149B.2008.07.1.0
www.analogictech.com
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