PRODUCT DATASHEET
AAT1140
SwitchRegTM
FastTransient 600mA Step-Down Converter
Step-Down Converter Design Example
Specifications
VO = 1.8V @ 600mA (adjustable using 0.6V version), Pulsed Load ΔILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 1.4MHz
TAMB = 85°C
1.8V Output Inductor
μsec
A
μsec
A
(use 4.7μH; see Table 1)
1.8V = 5.4μH
L1 = 3
VO2 = 3
For Sumida inductor CDRH3D16, 4.7μH, DCR = 105mΩ.
VO
L1 F
VO
VIN
1.8
V
1.8V
4.2V
ΔIL1 =
1 -
=
1 -
= 156mA
4.7μH 1.4MHz
ΔIL1
2
IPKL1 = IO +
= 0.6A + 0.068A = 0.668A
2
PL1 = IO DCR = 0.6A2 105mΩ = 38mW
1.8V Output Capacitor
VDROOP = 0.1V
3 · ΔILOAD
3 · 0.3A
COUT
=
=
= 6.4μF; use 10µF
VDROOP · FS
0.1V · 1.4MHz
(VO) · (VIN(MAX) - VO)
L1 · F · VIN(MAX)
1
1.8V · (4.2V - 1.8V)
1
·
= 45mArms
IRMS
=
·
=
4.7μH · 1.4MHz · 4.2V
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10μW
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN =
=
= 4.87µF; use 4.7µF
VPP
IO
25mV
0.6A
- ESR · 4 · FS
- 5mΩ · 4 · 1.4MHz
IO
2
IRMS
=
= 0.3Arms
P = esr · IRMS2 = 5mΩ · (0.3A)2 = 0.45mW
w w w . a n a l o g i c t e c h . c o m
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1140.2007.12.1.1
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
