AATIAN18 Datasheet, PDF (1/5 Pages) SiGe Semiconductor, Inc. – 1MHz 0.4A Buck Converter

EV-106
AAT1143EVAL
1MHz 0.4A Buck Converter
Introduction
The AAT1143 evaluation board demonstrates performance, as well as suggested size and placement of exter-
nal components, for the AAT1143 integrated buck regulator. The external components are selected for mini-
mum size and optimum operation up to 400mA output current. Resistors R1 and R2 set the output voltage.
For improved transient response, a 100pF to 150pF capacitor can be used for C4, along with increasing the
value of C1 to 10µF. C3 is available for cases where additional external compensation is necessary; for most
applications it is not used. Refer to the AAT1143 datasheet for more details about this product.
Layout
As with all switching power supplies, the board layout for the AAT1143 is critical (see Figure 1). Special care
has been taken with the placement of external components. The input capacitor (C2) placement is critical. It
must be placed immediately adjacent to the AAT1143. As shown in Figure 2, 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
INTERNAL DOCUMENT ^{Figure 3). The trace is also routed to avoid the LX node and associated noise. Resistors R1 and R2 are placed}
as closely as possible to the AAT1143 in order to minimize the length of the trace for the high impedance node
associated with the OUT pin. This minimizes the potential for external noise associated with the power stage
DO NOT COPY ^{of the AAT1143 and other circuitry coupling into the feedback of the AAT1143. Please refer to Table 1 for}
AAT1143 evaluation board specifications.
1
2
3
Enable
V_IN
C4
V_OUT
C1
4.7µF
GND
GND
R1
L1
C3
R2
59k
LX
U1
AAT1143
1 _{EN PGND} 8
2 _{OUT PGND} 7
3 _{VIN PGND} 6
4 _{LX AGND} 5
C2
4.7µF
Figure 1: AAT1143 Evaluation Board Schematic for Enhanced
Transient Response Version; C4 = 100pF; C1 = 10µF.
Specification
Input Voltage
Output Error Voltage
Output Current
Test Conditions
Min
Typ
2.7
3.6
-3
0
Table 1: AAT1143 Evaluation Board Specifications.
EV-106.2005.04.1.1
Max
5.5
+3
0.4
Units
V
%
A
1