AAT1112
1.5A, 1.4MHz Step-Down Converter
Design Example
Specifications
VO
VIN
FS
3.3V @ 1.5A, Pulsed Load ΔILOAD = 1.5A
2.7V to 4.2V (3.6V nominal)
1.2MHz
TAMB 85°C in TDFN33-12 Package
Output Inductor
L1 = VO(µH) = 3.3µH; see Table 2.
For Sumida inductor CDRH4D28 3.3µH DCR = 49.2mΩ max.
⎛
⎞
⎠
VO
L1 ⋅ FS
VO1
VIN
⎠
3.3
V
3.3V
4.2V
⎛
⋅ 1 -
⎝
⎞
ΔI1 =
=
⋅ 1 -
= 179mA
⎝
3.3µH ⋅ 1.2MHz
ΔI
IPK1 = IO1
+
1 = 1.5A + 0.089A = 1.59A
2
PL1 = IO12 ⋅ DCR = 1.5A2 ⋅ 49.2mΩ = 110mW
Output Capacitor
VDROOP = 0.2V
3 · ΔILOAD
VDROOP · FS
3 · 1.5A
COUT
=
=
= 18.8µF; use 22µF
0.2V · 1.2MHz
(VOUT) · (VIN(MAX) - VOUT
)
1
3.3V · (4.2V - 3.3V)
1
·
= 52mArms
IRMS(MAX)
=
·
=
3.3µH · 1.2MHz · 4.2V
L · FS · VIN(MAX)
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (52mA)2 = 13.3µW
16
1112.2007.01.1.1
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
