AAT1147
High Efficiency, Low Noise, Fast Transient
400mA Step-Down Converter
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN =
=
= 3.11μF; use 4.7μF
⎛
⎝
VPP
IO
⎞
⎛
⎝
25mV
0.4A
⎞
· 4
- ESR
·
4
·
FS
- 5mΩ
· 1.4MHz
⎠
⎠
IO
IRMS
=
= 0.2Arms
2
P = esr
·
IRMS2 = 5mΩ
·
(0.2A)2 = 0.2mW
AAT1147 Losses
IO2 · (RDSON(H) · VO + RDSON(L) · [VIN -VO
])
PTOTAL
=
VIN
+ (tsw · FS · IO + IQ) · VIN
0.42 · (0.725
Ω
·
1.8V + 0.7Ω
4.2V
· [4.2V - 1.8V])
=
+ (5ns · 1.4MHz · 0.4A + 70μA) · 4.2V = 126mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 126mW = 105.1°C
16
1147.2006.05.1.0