AAT1143
1MHz 400mA Step-Down Converter
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN =
=
= 4.75µF
⎛ VPP
⎝ IO
⎞
⎛ 25mV
⎝ 0.4A
⎞
- ESR · 4 · FS
- 5mΩ · 4 · 1MHz
⎠
⎠
IO
IRMS
=
= 0.2Arms
2
P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW
AAT1143 Losses
IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN -VO])
PTOTAL
=
VIN
+ (tsw · F · IO + IQ) · VIN
0.42 · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V])
4.2V
=
+ (5ns · 1.0MHz · 0.4A + 50µA) · 4.2V = 122mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 122mW = 104.5°C
16
1143.2005.09.1.7