AAT2550
Total Power Solution for Portable Applications
2.5V Output Capacitor
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
0.2V · 1.4MHz
COUT
=
=
= 3.2μF
(VOUT) · (VIN(MAX) - VOUT
)
1
2.5V · (4.2V - 2.5V)
1
·
= 21mArms
IRMS(MAX)
=
·
=
10μH · 1.4MHz · 4.2V
L · FS · VIN(MAX)
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (21mA)2 = 2.2μW
1.8V Output Capacitor
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
COUT
=
=
= 3.2μF
0.2V · 1.4MHz
(VOUT) · (VIN(MAX) - VOUT
)
1
1.8V · (4.2V - 1.8V)
1
·
= 45mArms
IRMS(MAX)
=
·
=
4.7μH · 1.4MHz · 4.2V
L · FS · VIN(MAX)
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10μW
Input Capacitor
Input Ripple VPP = 25mV.
1
1
CIN =
=
= 6.8μF
⎛
⎝
VPP
⎞
⎠
⎛
⎝
25mV
0.8A
⎞
- ESR
·
4
·
FS
- 5mΩ
·
4
·
1.4MHz
IO1
+
IO2
⎠
IO1 + IO2
2
IRMS(MAX)
P = esr
=
·
= 0.4Arms
IRMS2 = 5mΩ
·
(0.4A)2 = 0.8mW
2550.2006.07.1.0
33
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
