APEK8499SLJ-01 Documentation

APPLICATIONS
INFORMATION
Using the Allegro A8499
Evaluation Board
INTRODUCTION
The A8499 evaluation board provides a quick
vehicle for evaluating the A8499 step-down regulator. The board is laid out to accept a variety of
external components, allowing flexibility to modify the board for a specific design.
The evaluation board can be ordered from
your local Allegro® MicroSystems representative or by using the Allegro Web site at
www.allegromicro.com, and following the links to
the Online Store.
This application note provides information
on the electrical characteristics of the evaluation board. A schematic diagram of the circuit is
shown in figure 2. In addition, the layouts of the
copper traces and the silkscreen markings are provided in figures 3 and 4. A table of recommended
external components is also provided.
For information on the electrical characteristics of the A8499 itself, refer to the datasheet for
the device, also available on the Allegro Web site.
ELECTRICAL CHARACTERISTICS
As described in the following sections, the evaluation board is provided already populated with
external components for certain range of input and
output voltages.
Input Voltage Range
Figure 1. The Allegro A8499 is provided in a robust,
lead (Pb) free 8-pin SOIC package with 100% mattte tin
leadframe plating. An exposed pad for thermal dissipation is
available on the bottom surface of the package.
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The evaluation board is populated for an 8 to 22 V
input range. If a higher input voltage is desired,
input capacitors C2 and C1.1 must be substituted
with appropriately rated components.
The board is designed to parallel the C2, C1.1,
C1.2 and C1.3 input capacitors. C1.2 and C1.3 are
not populated and provide space to use electrolyt-
Using the Allegro A8499
Evaluation Board
ic capacitors in place of C1.1. Please refer to the
A8499 datasheet for inductor and output capacitor
selection for different input voltage ranges.
nects the A8499 output pin (LX) to the VBIAS
pin. For the output voltage range of 3.3 to 5 V,
connecting output to VBIAS allows the regulator to derive the bias supply from output and
eliminate losses in the internal bias regulator. For
output <3.3 V or > 5 V, R5 must be removed.
Output Voltage
The evaluation board is populated for 5 V output.
Please refer to the A8499 datasheet for information on selecting the inductor (L1), the output capacitors (C4.1, C4.2, and C4.3), and the feedback
resistors (R1 and R2) for different output voltages.
The A8499 can operate using its internal bias
regulator or the bias supply input, VBIAS, can be
provided externally for output < 3.3 V or > 5 V.
The A8499 starts up with internal bias regulator.
On the evaluation board, R5 (0 Ohms) con-
Output Current
The evaluation board is designed to provide 1.5 A
continuous current. For lower output currents, the
inductor (L1), Schottky diode (D1) and output capacitors (C4.1, C4.2, and C4.3) can be optimized
to reduce cost and save space. The A8499 datasheet provides component selection criteria.
C2
0.01 μF/25 V
10% Ceramic
C3
0.01 μF/25 V
Ceramic
C1.1
22 μF/25 V
20% Ceramic
C1.2
47 μF/50 V
Aluminum
C1.3
47 μF/50 V
Aluminum
J1
12 V
J2
GND
L1
47 μH
128 mΩ 20%
U1
1
BOOT
2
ENB
3
TSET
4
GND
A8499
8
VIN
7
LX
6
VBIAS
5
FB
J3
5.0 V/1.5 A
R5
0 KΩ
C4.1
47 μF/6.3 V
Ceramic
R3
30.1 KΩ
R3
10 KΩ
D1
40 V/3.0 A
R4
0 KΩ
C4.2
120 μF/6.3 V
SP
C1.3
330 μF/6.3 V
Aluminum
J4
GND
R3
3.16 KΩ
P1
P2
Figure 2. A8499 Evaluation Board Schematic. Values indicated are those of the external components populated at shipment.
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Allegro MicroSystems, Inc.
2
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Using the Allegro A8499
Evaluation Board
Figure 3. Traces Layout for A8499 Evaluation Board
Figure 4. Silkscreen Layout for A8499 Evaluation Board
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for
its use; nor for any infringement of patents or other rights of third parties which may result from its use.
Copyright © 2005, Allegro MicroSystems, Inc.
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Allegro MicroSystems, Inc.
3
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
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