AAT1147 AAT, AAT1147 Datasheet - Page 13

• Manufacturer Part Number: AAT1147
• Description: Step-Down Converter
• Manufacturer: AAT

The AAT1147, combined with an external feedfor-
ward capacitor (C4 in Figure 1), delivers enhanced
transient response for extreme pulsed load appli-
cations. The addition of the feedforward capacitor
typically requires a larger output capacitor C1 for
stability.
1147.2006.05.1.0
V
Table 2: Resistor Values For Use With 0.6V
OUT
1.85
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
2.0
2.5
3.3
(V)
Step-Down Converter.
R2 = 59kΩ Ω
R1 (kΩ Ω )
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
124
137
187
267
118
Figure 5: AAT1147 Evaluation Board Schematic.
V
10μF
GND
GND2
OUT
C1
R2 = 221kΩ Ω
V
IN
R1 (kΩ Ω )
1000
150
187
221
261
301
332
442
464
523
715
113
75
L1
4.7μH
R1
118k
Enable
High Efficiency, Low Noise, Fast Transient
1
2
3
59k
R2
LX
C1 10μF 10V 0805 X5R
C2 4.7μF 10V 0805 X5R
U1 AAT1147 SC70JW-8
L1 CDRH3D16-4R7
4.7μF
Thermal Calculations
There are three types of losses associated with the
AAT1147 step-down converter: switching losses,
conduction losses, and quiescent current losses.
Conduction losses are associated with the R
characteristics of the power output switching
devices. Switching losses are dominated by the
gate charge of the power output switching devices.
At full load, assuming continuous conduction mode
(CCM), a simplified form of the losses is given by:
I
The term t
down converter switching losses.
C2
Q
P
1
2
3
4
TOTAL
U1
AAT1147
is the step-down converter quiescent current.
EN
OUT
VIN
LX
400mA Step-Down Converter
+ (t
=
PGND
PGND
PGND
AGND
I
O
sw
sw
2
· (R
· F
8
7
6
5
is used to estimate the full load step-
S
DSON(H)
· I
O
+ I
· V
Q
) · V
O
+ R
V
IN
IN
DSON(L)
· [V
IN
- V
O
DS(ON)
])
13