AAT1152 Datasheet, PDF (15/18 Pages) Advanced Analogic Technologies – 850kHz 1A Synchronous Buck DC/DC Converter

AAT1152
850kHz 1A Synchronous Buck DC/DC Converter
Inductor Selection:
L
=
V_OUT
I_O ⋅ k ⋅
F
⋅
₁
-
V_OUT
V_IN 
=1.0A
⋅
1.5V
0.3 ⋅
830kHz
⋅
₁
-
1.5V
4.2V


=
3.9µH
Select Sumida inductor CDRH5D18 4.1µH 57mΩ 2.0 mm height.
∆I =
V_O
L⋅F
⋅
₁
-
V_O
V_IN


=
1.5V
4.1µH ⋅ 830kHz
⋅


1-
1.5V 
4.2V
= 280mA
I_PK
=
I_OUT
+
∆I
2
=
1.0A
+
0.14A
=
1.14A
P = I_O2 ⋅ DCR =57mW
Output Capacitor Dissipation:
I_RMS
=
1
2⋅
3^â‹
V_OUT ⋅ (V_IN
L⋅F⋅
- V_OUT)
V_IN
=
1
2⋅
3
⋅
1.5V
4.1µH
⋅
⋅
(4.2V - 1.5V)
830kHz ⋅ 4.2V
=82mA_RMS
P_ESR = ESR_COUT ⋅ I_RMS2 = 5mΩ ⋅ .082² A = 33µW
AAT1152 Dissipation:
P
=
I_O2
·
(R_DSON(H)
·
V_O +
V_IN
R_DSON(L)
·
(V_IN
-V_O))
+ (t_sw · F · I_O + I_Q) · V_IN
=
(0.14Ω
·
1.5V
+ 0.145Ω
3.6V
·
(3.6V
-
1.5V))
+
(20nsec
·
830kHz
·
1.0A
+
0.3mA)
·
3.6V
=
0.203W
T_J(MAX) = T_AMB + Θ_JA · P_LOSS = 85°C + 150°C/W · 0.203W = 115°C
1152.2003.01.0.9
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