AAT1146 Analogic Corporation, AAT1146 Datasheet - Page 15

• Manufacturer Part Number: AAT1146
• Manufacturer: Analogic Corporation

For the condition where the step-down converter is
in dropout at 100% duty cycle, the total device dis-
sipation reduces to:
Since R
losses all vary with input voltage, the total losses
should be investigated over the complete input
voltage range.
Given the total losses, the maximum junction tem-
perature can be derived from the θ
SC70JW-8 package which is 160°C/W.
Layout
The suggested PCB layout for the AAT1146 is
shown in Figures 2, 3, and 4. The following guide-
lines should be used to help ensure a proper layout.
1. The input capacitor (C2) should connect as
2. C1 and L1 should be connected as closely as
1146.2006.01.1.2
closely as possible to V
(Pins 6-8).
possible. The connection of L1 to the LX pin
should be as short as possible.
DS(ON)
P
TOTAL
T
J(MAX)
, quiescent current, and switching
= I
= P
O
2
· R
TOTAL
DSON(HS)
· Θ
IN
JA
(Pin 3) and PGND
+ I
+ T
Q
AMB
· V
IN
JA
for the
Fast Transient 400mA Step-Down Converter
3. The feedback trace or OUT pin (Pin 2) should
4. The resistance of the trace from the load return
A high density, small footprint layout can be
achieved using an inexpensive, miniature, non-
shielded, high DCR inductor. An evaluation board
is available with this inductor and is shown in
Figure 6. The total solution footprint area is 40mm
Figure 6: Minimum Footprint Evaluation Board
be separate from any power trace and connect
as closely as possible to the load point.
Sensing along a high-current load trace will
degrade DC load regulation. If external feed-
back resistors are used, they should be placed
as closely as possible to the OUT pin (Pin 2) to
minimize the length of the high impedance
feedback trace.
to the PGND (Pins 6-8) should be kept to a
minimum. This will help to minimize any error in
DC regulation due to differences in the poten-
tial of the internal signal ground and the power
ground.
Using 2.0mm x 1.6mm x 0.95mm Inductor.
AAT1146
15
2
.