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| AAT1121 Datasheet, PDF (16/20 Pages) Advanced Analogic Technologies – 1.5MHz, 250mA Step-Down Converter | |||
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AAT1121
1.5MHz, 250mA Step-Down Converter
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN =
â
â
VPP
IO
- ESRââ · 4 · FS
=
â 25mV
â 0.2A
= 1.38µF; use 4.7µF
- 5mΩââ · 4 · 1.5MHz
IRMS =
IO
2
= 0.1Arms
P = esr · IRMS2 = 5mΩ · (0.1A)2 = 0.05mW
AAT1121 Losses
PTOTAL
=
IO2
·
(RDSON(HS)
·
VO
+ RDSON(LS)
VIN
·
[VIN
-VO])
+ (tsw · F · IO + IQ) · VIN
0.22 · (0.7Ω · 1.8V + 0.7Ω · [4.2V - 1.8V])
=
4.2V
+ (5ns · 1.5MHz · 0.2A + 30µA) · 4.2V = 34.5mW
TJ(MAX) = TAMB + ÎJA · PLOSS = 85°C + (50°C/W) · 34.5mW = 86.7°C
16
1121.2006.04.1.0
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