AAT1156
1MHz 700mA Step-Down DC-DC Converter
Design Example
Specifications
IOUT
0.7A
IRIPPLE 40% of Full Load at Max VIN
VOUT 2.5V
VIN
FS
2.7V to 4.2V (3.6V nominal)
1MHz
TAMB 85°C
Maximum Input Capacitor Ripple:
V
V
O
⎛
⎞
⎠
O
IRMS = IO ·
· 1-
= 0.34Arms, VIN = 2 x VO
⎝
V
V
IN
IN
P = esr · IRMS2 = 5mΩ · 0.342 A = 0.6mW
Inductor Selection:
VOUT
IO ⋅ k ⋅ F
⎛
VOUT
VIN
⎞
⎠
2.5
V
2.5V
4.2V
⎛
⎞
⎠
L =
⋅ 1 -
⎝
=
⋅ 1 -
⎝
= 4.82µH
0.7A ⋅ 0.3 ⋅ 1MHz
Select Sumida inductor CDRH3D16 or CDRH4D28 4.7µH.
⎛
⎞
2.5V
⎠
4.2V
VO
L ⋅ F
VO
VIN
2.5
V
⎛
⎞
⎠
∆I =
⋅ 1 -
⎝
=
⋅ 1-
= 220mA
⎝
4.7µH ⋅ 1MHz
∆I
2
IPK = IOUT
+
= 0.7A + 0.11A = 0.81A
P = IO2 ⋅ DCR = (0.7A)2 ⋅ 80mΩ = 40mW
1156.2005.11.1.2
11
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
