aat1155iks-2.5-t1 Advanced Analogic Technologies, Inc., aat1155iks-2.5-t1 Datasheet - Page 11

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

Schottky Freewheeling Diode
The Schottky average current is the load current
multiplied by one minus the duty cycle.
For V
current is:
With a 125°C maximum junction temperature and a
120°C/W thermal resistance, the maximum aver-
age current is:
For overload, short-circuit, and excessive ambient
temperature conditions, the AAT1155 enters over-
temperature shutdown mode protecting the
AAT1155 as well as the output Schottky. In this
mode, the output current is limited internally until
the junction temperature reaches the temperature
limit (see over-temperature characteristics graphs).
The diode reverse voltage must be rated to with-
stand the input voltage.
1155.2006.09.1.7
I
AVG
I
AVG
IN
= I
=
at 5V and V
T
O
J(MAX)
·
θ
JA
⎛
⎝
1
-
· V
-
T
V
V
AMB
F
IN
O
⎞
⎠
OUT
⎛
⎝
=
=
1
120
-
2.5
125
at 3.3V, the average diode
V
V
IN
O
A
°C
° -
⎞
⎠
·
C
100µF
⎛
⎝
/
Vin 3.5V-5.5V
C4
1
W
-
70
rtn
·
5.0V
3.3
0.4
10µF
C1
°
C
Figure 2: 3.3V, 3A Output Efficiency.
C1 Murata 10µF 6.3V X5R GRM42-6X5R106K6.3
C2 Vishay 120µF 6.3V 594D127X96R6R3C2T
C3 0. 1 µF 0603ZD104M AVX
C4 Vishay Sprague 100µF 16V 595D107X0016C 100µF 16V
D1 B340LA Diodes Inc.
L1 CDRH6D28-1.5µH Sumida
Options
C2 MuRata 100µF 6.3V GRM43-2 X5R 107M 100µF 6.3V (two or three in parallel)
C2 TDK 100µF 6.3V C3325X5R0J107M 100µF 6.3V (two or three in parallel)
V
V
⎞
⎠
R1
100
= 1.14A
=
0.85A
R2
100k
C3
0.1µF
1MHz 2.5A Step-Down DC/DC Converter
AAT1155-3.3
FB
GND
EN
VCC
U1
LX
LX
VP
VP
3A Surface Mount Schottky Diodes
Input Capacitor Selection
The primary function of the input capacitor is to pro-
vide a low impedance loop for the edges of pulsed
current drawn by the AAT1155. A low ESR/ESL
ceramic capacitor is ideal for this function. To mini-
mize stray inductance, the capacitor should be
placed as closely as possible to the IC. This also
keeps the high frequency content of the input cur-
rent localized, minimizing the radiated and con-
ducted EMI while facilitating optimum performance
of the AAT1155. Proper placement of the input
capacitor C1 is shown in the layout in Figure 2.
Ceramic X5R or X7R capacitors are ideal. The
size required will vary depending on the load, out-
put voltage, and input voltage source impedance
characteristics. Typical values range from 1µF to
10µF. The input capacitor RMS current varies with
the input voltage and the output voltage. It is high-
est when the input voltage is double the output volt-
age where it is one half of the load current.
Diodes Inc.
Micro Semi
ROHM
Vout 3.3V @ 2.5A
B340LA
D1
L1
1.5µH
I
RMS
C2
120µF
=
I
O
+
-
·
RB050L-40
V
V
5820SM
B340LA
O
IN
·
⎛
⎝
1
-
V
V
IN
O
⎞
⎠
AAT1155
0.45V @ 3A
0.46V @ 3A
0.45 @ 3A
11