AAT2550_08 Datasheet, PDF (32/34 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications

SystemPower^TM
PRODUCT DATASHEET
AAT2550178
Total Power Solution for Portable Applications
2.5V Output Capacitor
C_OUT
=
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 0.3A
0.2V · 1.4MHz
=
3.2μF
I_RMS(MAX)
=
1
2·
3
·
(V_OUT) · (V_IN(MAX) - V_OUT)
L · F_S · V_IN(MAX)
=
1 _· 2.5V · (4.2V - 2.5V)
2· 3 ^{10μH · 1.4MHz · 4.2V}
= 21mArms
P_esr = esr · I_RMS2 = 5mΩ · (21mA)² = 2.2μW
1.8V Output Capacitor
C_OUT
=
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 0.3A
0.2V · 1.4MHz
= 3.2μF
I_RMS(MAX)
=
1
2·
3
·
(V_OUT) · (V_IN(MAX) - V_OUT)
L · F_S · V_IN(MAX)
=
1 _· 1.8V · (4.2V - 1.8V) _{= 45mArms}
2· 3 ^{4.7μH · 1.4MHz · 4.2V}
P_esr = esr · I_RMS2 = 5mΩ · (45mA)² = 10μW
Input Capacitor
Input Ripple V_PP = 25mV.
1
1
C_IN =
⎛ V_PP
⎝ I_O1 + I_O2
- ESR^⎞⎠ · 4 · F_S
=
= 6.8μF
⎛ 25mV
⎝ 0.8A
- 5mΩ⎞⎠ · 4 · 1.4MHz
I = _RMS(MAX)
I_O1 + I_O2
2
= 0.4Arms
P = esr · I_RMS2 = 5mΩ · (0.4A)² = 0.8mW
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2550.2008.02.1.3