aat1155iks-2.5-t1 Advanced Analogic Technologies, Inc., aat1155iks-2.5-t1 Datasheet - Page 13

• Manufacturer Part Number: aat1155iks-2.5-t1
• Description: Aat1155 | 1mhz 2.5a Step-down Dc/dc Converter
• Manufacturer: Advanced Analogic Technologies, Inc.

Thermal
Losses associated with the AAT1155 output switch-
ing MOSFET are due to switching losses and con-
duction losses. The conduction losses are associ-
ated with the R
switching device. At the full load condition, assum-
ing continuous conduction mode (CCM), an accu-
rate calculation of the R
derived from the following equations:
R
Internal switch RMS current
D is the duty cycle and V
drop of the Schottky diode.
ΔI is the peak-to-peak inductor ripple current.
A simplified form of calculating the R
switching losses is given by:
where I
Once the total losses have been determined, the
junction temperature can be derived. The thermal
resistance (Θ
on an FR4 printed circuit board in still air is 150°C/W.
T
is the resultant maximum junction temperature.
1155.2006.09.1.7
AMB
DS(ON)
P =
is the maximum ambient temperature and T
Q
losses
is the AAT1155 quiescent current.
I
O
2
I
RMS
· R
JA
P
V
) for the MSOP-8 package mounted
=
DS(ON)
ON
DS(ON)
T
IN
J
=
⎛
⎝
= P θ
D
I
I
RMS
O
V
=
2
characteristics of the output
O
+
V
2
V
O
IN
·
Δ
+ t
12
JA
R
+
+
I
F
DS(ON)
2
SW
DS(ON)
V
V
+ T
is the forward voltage
⎞
⎠
F
F
·
· F
D
AMB
S
· I
losses can be
O
+ I
DS(ON)
Q
· V
IN
and
1MHz 2.5A Step-Down DC/DC Converter
J
Design Example
(see Figures 2 and 5 for reference)
I
I
V
V
F
T
Inductor Selection
Use standard value of 1.5µH
Sumida inductor Series CDRH6D38.
OUT
RIPPLE
S
MAX
OUT
IN
100
L
95
90
85
80
75
70
65
60
0.01
=
=
Figure 5: 5V Input, 3.3V Output.
I k F
2.5A · 0.4 · 1MHz
O
I
· ·
Δ =
V
PK
2.5A
40% of Full Load at Max V
2.5V
5V ±5%
1MHz
70°C
I
OUT
Efficiency vs. Load Current
=
=
=
3.3V
L · F
1.5μ
I
2.5A + 0.41 = 2.91A
S
OUT
·
V
(V
⎛
⎝
O
1
+
IN
Output Current (A)
3.3V
H MHz
S
-
0.1
Δ
= 5.0V; V
2
V
·
⎛
⎝
I
V
1
OUT
1
IN
-
⎞
⎠
V
V
·
IN
O
⎛
⎝
OUT
1
⎞
⎠
⎛
⎝
-
1-
= 3.3V)
5.25V
3.3V
5.25V
3.3V
1
AAT1155
⎞
⎠
IN
=
⎞
⎠
1.23μH
= 0.82A
10
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