AAT2505 Datasheet, PDF (21/26 Pages) Advanced Analogic Technologies – Dual Channel, Step-Down Converter/Linear Regulator

AAT2505
Dual Channel, Step-Down
Converter/Linear Regulator
1.8V Buck Input Capacitor
Input Ripple V_PP = 25mV
C_IN = _{⎛ VPP}
⎝ I_OBUCK
1
- ESR^⎞⎠ · 4 · F_S
=
1
= 4.75μF
⎛ 25mV
⎝ 0.4A
- 5mΩ⎞⎠ · 4 · 1.4MHz
I_RMS =
I_OBUCK
2
= 0.2Arms
P = esr · I_RMS2 = 5mΩ · (0.2A)² = 0.2mW
AAT2505 Total Losses
P_TOTAL
=
I2
OBUCK
·
(R_DSON(H)
·
V_OBUCK
+ R_DSON(L)
V_IN
·
[V_IN
-
V_OBUCK])
+ (t_sw · F_S · I_OBUCK + I_QBUCK + I_QLDO) · V_IN + (V_IN - V_OLDO) · I_OLDO
0.4² · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V])
=
4.2V
+ (5ns · 1.4MHz · 0.4A + 50µA +125µA) · 4.2V + (4.2V - 3.3V) · 0.3A = 395mW
T_J(MAX) = T_AMB + Θ_JA · P_LOSS = 85°C + (50°C/W) · 395mW = 105°C
2505.2006.06.1.1
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