AAT1149 Datasheet, PDF (17/20 Pages) Advanced Analogic Technologies – 3MHz Fast Transient 400mA Step-Down Converter

AAT1149
3MHz Fast Transient
400mA Step-Down Converter
Input Capacitor
Input Ripple V_PP = 25mV
1
1
C_IN = _{⎛ VPP}
⎝ I_O
- ESR^⎞⎠ · 4 · F_S
=
⎛ 25mV
⎝ 0.4A
= 1.45μF; use 2.2μF
- 5mΩ⎞⎠ · 4 · 3.0MHz
I_RMS =
I_O
2
= 0.2Arms
P = esr · I_RMS2 = 5mΩ · (0.2A)² = 0.2mW
AAT1149 Losses
P_TOTAL
=
I_O2
·
(R_DS(ON)H
·
V_O
+ R_DS(ON)L
V_IN
·
[V_IN
-V_O])
+ (t_sw · F_S · I_O + I_Q) · V_IN
0.4² · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V])
=
4.2V
+ (5ns · 3MHz · 0.4A + 70μA) · 4.2V = 140mW
T_J(MAX) = T_AMB + Θ_JA · P_LOSS = 85°C + (160°C/W) · 140mW = 107°C
1149.2006.11.1.0
17