AAT2505 Analogic Corporation, AAT2505 Datasheet - Page 20

• Manufacturer Part Number: AAT2505
• Manufacturer: Analogic Corporation

Step-Down Converter Design Example
Specifications
V
V
V
F
T
1.8V Buck Output Inductor
For Sumida inductor CDRH3D16, 4.7µH, DCR = 105mΩ.
1.8V Buck Output Capacitor
V
L1 = 3
ΔI
C
I
20
P
P
I
RMS
PKL1
S
AMB
OBUCK
OLDO
IN
DROOP
L1
OUT
esr
L1
= I
= esr · I
=
=
= I
=
L1 ⋅ F
O
µsec
2
V
O
2
= 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ΔI
= 3.3V @ 300mA
= 2.7V to 4.2V (3.6V nominal)
= 1.4MHz
= 85°C
= 0.1V
3 · ΔI
·
A
DROOP
⋅ DCR = 0.4A
1
V
+
O
3
ΔI
RMS
S
2
·
⋅ V
LOAD
L1
⋅ 1 -
(V
· F
2
⎛
⎝
= 0.4A + 0.068A = 0.468A
O2
= 5mΩ · (45mA)
O
L1 · F
S
) · (V
= 3
=
V
V
IN
0.1V · 1.4MHz
O
µsec
S
IN(MAX)
2
⎞
⎠
· V
A
⋅ 105mΩ = 17mW
3 · 0.3A
=
IN(MAX)
4.7μH ⋅ 1.4MHz
⋅ 1.8V = 5.4µH
- V
O
)
2
1.8 V
= 10 µ W
=
2
= 6.4 µ F; use 10 µ F
·
1
3
·
4.7 µ H · 1.4MHz · 4.2V
1.8V · (4.2V - 1.8V)
⋅ 1 -
⎛
⎝
(use 4.7µH; see Table 1)
1.8V
4.2V
⎞
⎠
= 156mA
= 45mArms
Converter/Linear Regulator
Dual Channel, Step-Down
LOAD
= 300mA
2505.2006.06.1.1