AAT1151 Datasheet, PDF (13/16 Pages) Advanced Analogic Technologies – 850kHz 700mA Synchronous Buck DC/DC Converter

AAT1151
850kHz 700mA Synchronous Buck DC/DC Converter
Design Example
Specifications
I_OUT
I_RIPPLE
V_OUT
V_IN
F_S
T_AMB
0.7A
40% of Full Load at Max V_IN
1.5V
2.7V to 4.2V (3.6V nominal)
850kHz
85°C
Maximum Input Capacitor Ripple:
I_RMS = I_O ·
V_{O · ⎛1-}
V_IN ⎝
V_{O ⎞}
V_IN ⎠
= 0.35Arms,
V_IN
=
2
×
V_O
P = esr · I_RMS2 = 5mΩ · 0.35² A = 0.6mW
Inductor Selection:
L
=
V_OUT
I_O ⋅ k ⋅
F
⋅
⎛⎝₁
-
V_OUT⎞
V_IN ⎠
=0.7A
⋅
1.5V
0.4 ⋅ 850kHz
⋅
⎛⎝₁
-
1.5V
4.2V
⎞
⎠
=
4.05µH
Select Sumida inductor CDRH3D16 3.3µH 63mΩ 1.8mm height.
∆I =
V_O
L⋅F
⋅
⎛⎝₁
-
V_O
V_IN
⎞
⎠
=
1.5V
3.3µH ⋅ 850kHz
⋅
⎛⎝ _1-
1.5V ⎞
4.2V⎠
= 340mA
I_PK
=
I_OUT
+
∆I
2
=
0.7A
+
0.17A
=
0.87A
P = I_O2 ⋅ DCR = (0.7)² ⋅ 63mΩ = 31mW
Output Capacitor Ripple Current:
I_RMS =
1
2·
·
3
V_OUT · (V_IN - V_OUT)
L · F · V_IN
= ¹ · ^{1.5V · (4.2V - 1.5V)} = 99mArms
2· 3 ^{3.3µH · 850kHz · 4.2V}
Pesr = esr · I_RMS2 = 5mΩ · 99² mA = 50µW
1151.2005.11.1.4
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