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| AAT2120 Datasheet, PDF (16/20 Pages) Advanced Analogic Technologies – 500mA Low Noise Step-Down Converter | |||
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AAT2120
500mA Low Noise Step-Down Converter
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN = â VPP
â IO
- ESRââ · 4 · FS
=
â 25mV
â 0.2A
= 1.16µF (use 4.7µF)
- 5mΩââ · 4 · 1.8MHz
IRMS =
IO
2
= 0.1Arms
P = esr · IRMS2 = 5mΩ · (0.1A)2 = 0.05mW
AAT2120 Losses
PTOTAL
=
IO2
·
(RDS(ON)H
·
VO
+ RDS(ON)L
VIN
·
[VIN
-VO])
+ (tsw · FS · IO + IQ) · VIN
0.22 · (0.59Ω · 1.8V + 0.42Ω · [4.2V - 1.8V])
=
4.2V
+ (5ns · 1.8MHz · 0.2A + 45µA) · 4.2V = 19.71mW
TJ(MAX) = TAMB + ÎJA · PLOSS = 85°C + (50°C/W) · 26.14mW = 86°C
16
2120.2007.10.1.1
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