PRODUCT DATASHEET
AAT1149A
TM
SwitchReg
2.2MHz FastTransient 400mA Step-Down Converter
Step-Down Converter Design Example
Specifications
VO = 1.875V @ 400mA (adjustable using 0.6V version), Pulsed Load DILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 2.2MHz
TAMB = 85°C
1.875V Output Inductor
µs
µs
A
(use 2.2μH)
L1 = 1 · VO = 1
A
· 1.875V = 1.875µH
For Taiyo Yuden inductor CBC2518T2R2M, 2.2μH, DCR = 130mΩ.
VO
L1 · FS
VO
VIN
1.875
V
1.875V
4.2V
ΔIL1 =
· 1 -
=
· 1 -
= 214mA
2.2µH · 2.2MHz
ΔI
IPKL1 = IO + L1 = 0.4A + 0.107A = 0.507A
2
PL1 = IO2 · DCR = 0.4A2 · 130mΩ = 21mW
1.875V Output Capacitor
VDROOP = 0.1V
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
0.1V · 2.2MHz
COUT
=
=
= 4.1µF; use 4.7µF
(VO) · (VIN(MAX) - VO)
L1 · FS · VIN(MAX)
1
1.875V · (4.2V - 1.875V)
2.2µH · 2.2MHz · 4.2V
1
·
= 62mArms
IRMS
=
·
=
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (62mA)2 = 19µW
w w w . a n a l o g i c t e c h . c o m
1149A.2008.08.1.1
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