AAT1146 Analogic Corporation, AAT1146 Datasheet - Page 14

• Manufacturer Part Number: AAT1146
• Manufacturer: Analogic Corporation

The adjustable version of the AAT1146, combined
with an external feedforward capacitor (C4 in
Figure 1), delivers enhanced transient response for
extreme pulsed load applications. The addition of
the feedforward capacitor typically requires a larg-
er output capacitor C1 for stability.
14
Table 2: Adjustable Resistor Values For Use
V
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)
With 0.6V 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
118
124
137
187
267
Figure 5: AAT1146 Adjustable Evaluation Board Schematic.
V
10µF
GND
GND2
OUT
C1
R2 = 221kΩ Ω
V
IN
1.00M
150K
187K
221K
261K
301K
332K
442K
464K
523K
715K
113K
75K
R1
L1
4.7µH
Fast Transient 400mA Step-Down Converter
R1
118k
Enable
1
2
3
59k
R2
LX
C1 10µF 10V 0805 X5R
C2 4.7µF 10V 0805 X5R
U1 AAT1146 SC70JW-8
L1 CDRH3D16-4R7
4.7µF
Thermal Calculations
There are three types of losses associated with
the AAT1146 step-down converter: switching loss-
es, conduction losses, and quiescent current loss-
es. Conduction losses are associated with the
R
ing devices. Switching losses are dominated by
the gate charge of the power output switching
devices. At full load, assuming continuous con-
duction mode (CCM), a simplified form of the LDO
losses is given by:
I
The term t
down converter switching losses.
C2
P
Q
1
2
3
4
DS(ON)
TOTAL
U1
AAT1146
is the step-down converter quiescent current.
EN
OUT
VIN
LX
+ (t
=
PGND
PGND
PGND
AGND
characteristics of the power output switch-
I
O
sw
sw
2
· (R
· F · I
8
7
6
5
is used to estimate the full load step-
DSON(HS)
O
+ I
Q
) · V
· V
O
IN
+ R
V
IN
DSON(LS)
AAT1146
1146.2006.01.1.2
· [V
IN
- V
O
])