AAT1141_0810 Datasheet, PDF (16/20 Pages) Advanced Analogic Technologies – Fast Transient 600mA Step-Down Converter

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PRODUCT DATASHEET
AAT1141
Fast Transient 600mA Step-Down Converter
Step-Down Converter Design Example
Specifications
V_O =
V_IN =
F_S =
T_AMB =
1.8V @ 600mA (adjustable using 0.6V version), Pulsed Load ΔI_LOAD = 300mA
2.7V to 4.2V (3.6V nominal)
2MHz
85°C
1.8V Output Inductor
µs
µs
L1 = 3 _A · V_O2 = 3 _A · 1.8V = 5.4µH (use 4.7μH; see Table 1)
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105mΩ.
ΔI_L1 =
V_O
L1 · F
·
1-
V_O
V_IN
=
1.8V
4.7µH · 2MHz
·
1
-
1.8V
4.2V
= 109.2mA
I_PKL1
=
I_O
+
ΔI_L1
2
=
0.6A
+
0.055A
=
0.655A
P_L1 = I_O2 · DCR = 0.6A² · 105mΩ = 38mW
1.8V Output Capacitor
V_DROOP = 0.1V
C_OUT
=
3 · ΔI_LOAD
V_DROOP · F_S
=
3 · 0.3A
0.1V · 2MHz
= 4.48µF; use 10µF
I_RMS
=
1 _· (V_O) · (V_IN(MAX) - V_O) ₌ 1
2· 3
L1 · F · V_IN(MAX)
2·
·
3
1.8V · (4.2V - 1.8V)
4.7µH · 2MHz · 4.2V
= 31.5mArms
P_esr = esr · I_RMS2 = 5mΩ · (31.5mA)² = 5µW
Input Capacitor
Input Ripple V_PP = 25mV
C_IN =
1
=
V_PP
I_O
- ESR
· 4 · F_S
1
= 3.4µF; use 4.7µF
25mV
0.6A
- 5mW · 4 · 2MHz
I_RMS =
I_O
2
= 0.3Arms
P = esr · I_RMS2 = 5mΩ · (0.3A)² = 0.45mW
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1141.2008.10.1.6