AAT2552 Datasheet, PDF (28/33 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications

AAT2552
Total Power Solution for Portable Applications
Step-Down Converter Design Example (to be updated)
Specifications
V_O = 1.8V @ 250mA, Pulsed Load ΔI_LOAD = 200mA
V_IN = 2.7V to 4.2V (3.6V nominal)
F_S
= 1.5MHz
T_AMB = 85°C
1.8V Output Inductor
µsec
µsec
L1 = 1.67 _A ⋅ V_O2 = 1.67 _A ⋅ 1.8V = 3µH _{(use 3.0µH; see Table 3)}
For Sumida inductor CDRH2D09-3R0, 3.0µH, DCR = 150mΩ.
ΔI_L1 =
V_O
L1 ⋅ F_S
⋅ ^⎛⎝1 -
V_O ⎞
V_IN ⎠
=
1.8V
3.0µH ⋅ 1.5MHz
⋅
⎛
⎝
1
-
1.8V
4.2V
⎞
⎠
= 228mA
I_PKL1
=
I_O
+
ΔI_L1
2
=
250mA
+
114mA
=
364mA
P_L1 = I_O2 ⋅ DCR = 250mA² ⋅ 150mΩ = 9.375mW
1.8V Output Capacitor
V_DROOP = 0.1V
C_OUT
=
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 0.2A
0.1V · 1.5MHz
= 4µF (use 4.7µF)
I_RMS
=
1 _· (V_O) · (V_IN(MAX) - V_O) ₌ 1 _·
2· 3
L1 · F_S · V_IN(MAX) 2· 3
1.8V · (4.2V - 1.8V) _{= 66mArms}
3.0µH · 1.5MHz · 4.2V
P_esr = esr · I_RMS2 = 5mΩ · (66mA)² = 21.8µW
28
2552.2007.04.1.0