AAT1149 Analogic Corporation, AAT1149 Datasheet - Page 16

• Manufacturer Part Number: AAT1149
• Manufacturer: Analogic Corporation

Step-Down Converter Design Example
Specifications
V
V
F
T
1.8V Output Inductor
For Taiyo Yuden inductor CBC2518T2R2M, 2.2μH, DCR = 130mΩ.
1.8V Output Capacitor
V
16
C
L1 = 1
ΔI
P
I
P
I
RMS
PKL1
S
AMB
O
IN
DROOP
esr
L1
OUT
L1
= I
= esr · I
=
=
= I
=
O
μsec
2
L1 ⋅ F
V
O
2
= 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ΔI
= 2.7V to 4.2V (3.6V nominal)
= 3.0MHz
= 85°C
= 0.1V
3 · ΔI
·
A
DROOP
1
⋅ DCR = 0.4A
+
V
3
O
ΔI
RMS
2
·
⋅ V
S
LOAD
L1
(V
⋅ 1 -
· F
2
= 0.4A + 0.078A = 0.478A
O
⎛
⎝
L1 · F
= 5mΩ · (45mA)
O
S
) · (V
= 1
=
V
V
μsec
0.1V · 3.0MHz
S
IN
IN(MAX)
O
2
A
· V
⎞
⎠
⋅ 130mΩ = 21mW
3 · 0.3A
=
IN(MAX)
⋅ 1.8V = 1.8μH
2.2μH ⋅ 3.0MHz
- V
O
)
2
1.8 V
= 10μW
=
2
= 3.0μF; use 4.7µF
·
1
3
·
2.2μH · 3.0MHz · 4.2V
1.8V · (4.2V - 1.8V)
⋅ 1 -
(use 2.2μH; see Table 1)
⎛
⎝
1.8V
4.2V
⎞
⎠
= 156mA
= 45mArms
400mA Step-Down Converter
LOAD
3MHz Fast Transient
= 300mA
1149.2006.11.1.0