AAT1143 Advanced Analogic Technologies, AAT1143 Datasheet - Page 13

• Manufacturer Part Number: AAT1143
• Description: 1MHz 400mA Step-Down Converter
• Manufacturer: Advanced Analogic Technologies

The adjustable version of the AAT1143, 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.
1143.2005.09.1.7
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
(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
Figure 5: AAT1143 Adjustable Evaluation Board Schematic.
V
4.7µF
GND
GND2
OUT
C1
R2 = 221kΩ Ω
R1 (kΩ Ω )
V
IN
150
187
221
261
301
332
442
464
523
715
113
75
L1
4.7µH
R1
118k
Enable
1
2
3
59k
R2
LX
C1, C2 4.7µF 10V 0805 X5R
U1 AAT1143 SC70JW-8
L1 CDRH3D16-4R7
1MHz 400mA Step-Down Converter
Thermal Calculations
There are three types of losses associated with
the AAT1143 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.
Q
P
4.7µF
DS(ON)
C2
TOTAL
is the step-down converter quiescent current.
1
2
3
4
U1
AAT1143
EN
OUT
VIN
LX
+ (t
=
characteristics of the power output switch-
I
PGND
PGND
PGND
AGND
O
sw
sw
2
· (R
· F · I
is used to estimate the full load step-
8
7
6
5
DSON(HS)
O
+ I
Q
) · V
· V
O
IN
+ R
V
IN
DSON(LS)
AAT1143
· [V
IN
- V
O
])
13