AATIAN28 Datasheet, PDF (1/6 Pages) SiGe Semiconductor, Inc. – 1MHz 2.5A Buck DC/DC Converter

EV-107
AAT1155 EVAL
1MHz 2.5A Buck DC/DC Converter
Introduction
The AAT1155 evaluation board demonstrates performance, along with the suggested size and placement of
external components, for the AAT1155 integrated buck regulator. The external components are selected for
minimum size and optimum operation up to 2.5A output current. Please refer to the AAT1155 product
datasheet for more details about this product.
Component Summary
Capacitor C4 is a high equivalent series resistance (ESR) tantalum capacitor for damping the high Q input
network associated with the inductance of the leads feeding the input power to the evaluation board and the
low ESR 10µF ceramic input capacitor (C1). R2 is a pull-up resistor to allow the enable pin to be used to
enable and disable the IC by either shorting the enable pin to GND or leaving the pin open. Both R2 and C4
are for demonstration purposes only and are not necessary in the final solution. Resistors R3 and R4 are used
with the 1V model to set the output voltage to any desired value from 1.0V to as high as 200mV below the
minimum input voltage. They are not required for the fixed output voltage versions of the AAT1155. For fixed
output voltage versions, R4 is omitted and R3 is replaced with a short.
Layout
As with all switching power supplies, the board layout for the AAT1155 is critical (see Figure 1). Special care has
been taken with the placement of the external components. The input capacitor (C1) placement is critical and it
must be located immediately adjacent to the AAT1155. As shown in Figure 2, the LX node trace has been rout-
ed under C1 in order to facilitate placement of C1 close to the IC. The output voltage feedback trace has been
routed on the portion of the back side of the board which has a ground plane on the top side (see Figure 3). The
trace is routed to avoid the LX node and associated noise.
VIN+
C4
100µF
Enable
R1
100
R2
100k
C1
10µF
C3
0.1µF
R3
R4
10.0k
U1
AAT1155
1 _{FB VP} 8
2 _{GND LX} 7
3 _{EN LX} 6
4 _{VCC VP} 5
VOUT+
LX
L1
1.5µH
CR1 C2
B340LA 120µF
GND
C1: Murata 10µF 6.3V X5R GRM42-6X5R106K6.3
Figure 1: AAT1155 Evaluation Board Schematic.
EV-107.2005.01.1.0
1