AAT1143IJS-1.5-T1 View Datasheet(PDF) - Advanced Analogic Technologies
Part Name
Description
MFG CO.
'AAT1143IJS-1.5-T1' PDF : 20 Pages View PDF
AAT1143
1MHz 400mA Step-Down Converter
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.
VOUT (V)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
R2 = 59kΩ
R1 (kΩ)
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
R2 = 221kΩ
R1 (kΩ)
75
113
150
187
221
261
301
332
442
464
523
715
Table 2: Adjustable Resistor Values For Use
With 0.6V Step-Down Converter.
Thermal Calculations
There are three types of losses associated with the
AAT1143 step-down converter: switching losses,
conduction losses, and quiescent current losses.
Conduction losses are associated with the RDS(ON)
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:
PTOTAL
=
IO2
·
(RDS(ON)H
·
VO
+ RDS(ON)L
VIN
·
[VIN
-
VO])
+ (tsw · FS · IO + IQ) · VIN
IQ is the step-down converter quiescent current.
The term tsw is used to estimate the full load step-
down converter switching losses.
VIN
VOUT
C1
4.7μF
GND
1
2
3
Enable
R1
118k
L1
4.7μH
R2
59k
U1
AAT1143
1 EN PGND 8
2 OUT PGND 7
3 VIN PGND 6
4 LX AGND 5
C2
4.7μF
GND2
LX
U1 AAT1143 SC70JW-8
L1 CDRH3D16-4R7
C1, C2 4.7μF 10V 0805 X5R
Figure 5: AAT1143 Adjustable Evaluation Board Schematic.
1143.2006.07.1.10
13
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