DATA SHEET
AAT1120
500mA Step-Down Converter
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN = ⎛ VPP
⎝ IO
- ESR⎞⎠ · 4 · FS
=
⎛ 25mV
⎝ 0.2A
= 1.38µF (use 4.7µF)
- 5mΩ⎞⎠ · 4 · 1.5MHz
IRMS =
IO
2
= 0.1Arms
P = esr · IRMS2 = 5mΩ · (0.1A)2 = 0.05mW
AAT1120 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 · 1.5MHz · 0.2A + 30µA) · 4.2V = 26.14mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 26.14mW = 86.3°C
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
16
201973B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013