AAT1120 Advanced Analogic Technologies, Inc., AAT1120 Datasheet - Page 15

• Manufacturer Part Number: AAT1120
• Description: Aat1120 | 500ma Step-down Converter
• Manufacturer: Advanced Analogic Technologies, Inc.

Step-Down Converter Design Example
Specifications
V
V
F
T
1.8V Output Inductor
For Sumida inductor CDRH2D09-3R0, 3.0μH, DCR = 150mΩ.
1.8V Output Capacitor
V
L1 = 1.67
ΔI
C
I
1120.2007.01.1.0
P
P
I
RMS
PKL1
S
AMB
O
IN
DROOP
L1
esr
OUT
L1
= I
= esr · I
=
=
= I
=
O
2
L1 ⋅ F
V
O
2
= 1.8V @ 250mA, Pulsed Load ΔI
= 2.7V to 4.2V (3.6V nominal)
= 1.5MHz
= 85°C
= 0.1V
3 · ΔI
·
DROOP
⋅ DCR = 250mA
1
V
+
µsec
O
3
ΔI
RMS
A
2
·
S
LOAD
L1
(V
⋅ 1 -
· F
2
= 250mA + 114mA = 364mA
= 5mΩ · (66mA)
⎛
⎝
O
⋅ V
L1 · F
S
) · (V
O2
=
V
V
= 1.67
0.1V · 1.5MHz
IN(MAX)
O
IN
S
⎞
⎠
· V
3 · 0.2A
2
=
⋅ 150mΩ = 9.375mW
IN(MAX)
- V
3.0µH ⋅ 1.5MHz
µsec
A
O
)
2
1.8 V
= 21.8µW
=
⋅ 1.8V = 3µH
2
= 4µF (use 4.7µF)
·
1
3
·
3.0µH · 1.5MHz · 4.2V
LOAD
1.8V · (4.2V - 1.8V)
⋅ 1 -
⎛
⎝
= 200mA
(use 3.0μH; see Table 1)
1.8V
4.2V
⎞
⎠
= 228mA
= 66mArms
500mA Step-Down Converter
AAT1120
15