AAT1112 View Datasheet(PDF) - Advanced Analogic Technologies
Part Name
Description
MFG CO.
'AAT1112' PDF : 20 Pages View PDF
SwitchRegTM
PRODUCT DATASHEET
AAT1112
1.5A, 1.4MHz Step-Down Converter
Design Example
Specifications
VO 3.3V @ 1.5A, Pulsed Load ΔILOAD = 1.5A
VIN 2.7V to 4.2V (3.6V nominal)
FS 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.
ΔI1 =
VO
L1 ⋅ FS
⋅
⎛⎝1 -
VO1⎞
VIN ⎠
=
3.3V
3.3µH ⋅ 1.2MHz
⋅
⎛⎝1 -
3.3V ⎞
4.2V ⎠
= 179mA
IPK1
=
IO1
+
ΔI1
2
=
1.5A
+
0.089A
=
1.59A
PL1 = IO12 ⋅ DCR = 1.5A2 ⋅ 49.2mΩ = 110mW
Output Capacitor
VDROOP = 0.2V
COUT
=
3 · ΔILOAD
VDROOP · FS
=
3 · 1.5A
0.2V · 1.2MHz
= 18.8µF; use 22µF
I = RMS(MAX)
1
2·
· (VOUT) · (VIN(MAX) - VOUT)
3
L · FS · VIN(MAX)
=1
2·
3
·
3.3V · (4.2V - 3.3V)
3.3µH · 1.2MHz · 4.2V
= 52mArms
Pesr = esr · IRMS2 = 5mΩ · (52mA)2 = 13.3µW
Input Capacitor
Input Ripple VPP = 50mV
1
1
CIN =
⎛
⎝
VPP -
IO1 + IO2
ESR⎞⎠
·
4
·
FS
=
⎛ 50mV
⎝ 1.5A
= 7.3µF; use 10µF
- 5mΩ⎞⎠ · 4 · 1.2MHz
I = RMS(MAX)
IO
2
= 0.75Arms
P = esr · IRMS2 = 5mΩ · (0.75A)2 = 3mW
16
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1112.2007.11.1.2
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