AAT1154 Ver la hoja de datos (PDF) - Analog Technology Inc
Número de pieza
componentes Descripción
Fabricante
AAT1154 Datasheet PDF : 16 Pages
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SwitchRegTM
Design Example
(See Figures 1 and 4 for reference)
IOUT
IRIPPLE
VOUT
VIN
FS
TMAX
3A
30% of Full Load at Max VIN
3.3V
5V ±5%
1MHz
70°C
Inductor Selection
L = VOUT · ⎛1- VOUT⎞
IO · k · FS ⎝ VIN ⎠
=
3A ·
3.3V
0.3 ·1MHz
·⎛⎝1-
3.3V⎞
5V ⎠
=
1.25μH
Use standard value of 1.5μH
Sumida Inductor Series CDRH6D38.
ΔI
=
VO
L · FS
⎝⎛1-
VO
VIN
⎞
⎠
3.3V
= 1.5μH ·1MHz
⎛⎝1
-
3.3V ⎞
5.25V⎠
= 0.82A
I PK
=
IOUT +
ΔI
2
= 3A + 0.41A = 3.41A
Efficiency vs. Load Current
(VIN = 5V; VOUT = 3.3V)
100
95
90
85
80
75
70
65
60
0.01
0.1
1
10
Output Current (A)
Figure 4: 5V Input, 3.3V Output.
PRODUCT DATASHEET
AAT1154
1MHz 3A Step-Down DC/DC Converter
AAT1154 Junction Temperature
PON
=
IO2
·
RDS(ON)
VIN
·
VO
+ ⎛ tSW
⎝
·
FS
2
·
IO
+
IQ⎠⎞
·
VIN
=
=
32
·
65mΩ
5V
·
3.3V
+
⎛ 20ns
⎝
·
1MHz
2
·
3A
+ 750μA⎞⎠ · 5V
= 0.539 Watts
TJ(MAX)= TAMB + ΘJA · P
= 70°C +110°C /W · 0.54W = 129°C
Diode
IDIODE= IO · ⎝⎛1-
VO ⎞
VIN ⎠
=
3A · ⎛⎝1 -
3.3V ⎞
5V ⎠
= 1.02A
VF = 0.35V
PDIODE · VF · IDIODE
0.35V ·1.01A = 0.354W
Given an ambient thermal resistance of 120°C/W from
the manufacturer’s data sheet, TJ(MAX) of the diode is:
TJ(MAX)= TAMB + ΘJA · P
= 70°C +120°C /W · 0.354W
= 112°C
Output Capacitor
The output capacitor value required for sufficient loop
phase margin depends on the type of capacitor selected.
For a low ESR ceramic capacitor, a minimum value of
200μF is required. For a low ESR tantalum capacitor,
lower values are acceptable. While the relatively higher
ESR associated with the tantalum capacitor will give
more phase margin and a more dampened transient
response, the output voltage ripple will be higher.
The 120μF Vishay 594D tantalum capacitor has an ESR
of 85mΩ and a ripple current rating of 1.48Arms in a C
case size. Although smaller case sizes are sufficiently
rated for this ripple current, their ESR level would result
in excessive output ripple.
1154.2007.11.1.7
www.analogictech.com
13
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