AAT2500M Datasheet, PDF (19/22 Pages) Advanced Analogic Technologies – 400mA Step-Down Converter and 300mA LDO

AAT2500M
400mA Step-Down Converter and 300mA LDO
Input Capacitor
Input Ripple V_PP = 25mV
1
1
C_IN = _{⎛ VPP}
⎝ I_OBUCK
- ESR^⎞⎠ · 4 · F_OSC
=
= 2.42µF
⎛
⎝
25mV
0.4A
- 5mΩ⎞⎠ · 4 · 1.8MHz
I_RMS
=
I_OBUCK
2
= 0.2A_RMS
P = esr · I_RMS2 = 5mΩ · (0.2A)² = 0.2mW
AAT2500M Losses
P_TOTAL
=
I²
OBUCK
·
(R_DSON(HS)
·
V_OBUCK
+ R_DSON(LS)
V_IN
·
[V_IN
-
V_OBUCK])
+ (t_sw · F_OSC · I_OBUCK + I_QBUCK + I_QLDO) · V_IN + (V_IN - V_LDO) · I_LDO
(0.4A)² · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V])
=
4.2V
+ (5ns · 1.8MHz · 0.4A + 50µA +125µA) · 4.2V + (4.2V - 3.3V) · 0.3A = 399mW
T_J(MAX) = T_AMB + Θ_JA · P_LOSS = 85°C + (110°C/W) · 399mW = 129°C
2500M.2007.06.1.0
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