AAT2500
1MHz Step-Down Converter/LDO Regulator
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN =
=
= 4.75μF
⎛
⎝
VPP
IOBUCK
⎞
⎠
⎛
⎝
25mV
0.4A
⎞
- ESR
·
4
·
FS
- 5mΩ
· 4 · 1MHz
⎠
IOBUCK
IRMS
=
= 0.2Arms
IRMS2 = 5mΩ (0.2A)2 = 0.2mW
2
P = esr
·
·
AAT2500 Losses
IOBUCK2 · (RDSON(HS) · VOBUCK + RDSON(LS) · [VIN - VOBUCK
])
PTOTAL
=
VIN
+ (tsw · F · IOBUCK + IQBUCK + IQLDO) · VIN + (VIN - VLDO) · ILDO
0.42 · (0.725
Ω
·
1.8V + 0.7Ω
4.2V
· [4.2V - 1.8V])
=
+ (5ns · 1.0MHz · 0.4A + 50μA +125μA) · 4.2V + (4.2V - 3.3V) · 0.3A = 392mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 392mW = 105°C
2500.2006.05.1.16
21