EV-107

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 routed 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+
VOUT+
R1
100
C4
100µF
U1
AAT1155
R3
1
R2
100k
2
Enable
C1
10µF
C3
0.1µF
VP
8
GND LX
7
FB
3
EN
LX
6
4
VCC VP
5
LX
R4
10.0k
L1
1.5µH
C2
CR1
B340LA 120µF
GND
C1: Murata 10µF 6.3V X5R GRM42-6X5R106K6.3
Figure 1: AAT1155 Evaluation Board Schematic.
EV-107.2005.01.1.0
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EV-107
AAT1155 EVAL
1MHz 2.5A Buck DC/DC Converter
Specification
Test Conditions
Input Voltage
Output Error Voltage
Output Current
Min
Typ
Max
Units
2.7
3.6
±3
5.5
V
%
A
0
2.5
Table 1: AAT1155 Evaluation Board Specifications.
Figure 2: AAT1155 Evaluation
Board PCB Top Side.
Figure 3: AAT1155 Evaluation
Board PCB Bottom Side.
Test Equipment
1. 6V, 5A laboratory power supply: HP33401A or equivalent.
2. DC 0A to 2.5A load capable of operation down to 1.0V: Keithley 2400 or equivalent.
When using the Keithley 2400, set the meter to zero volts in voltage source mode and set the load current by varying the current compliance (maximum current) of the meter.
3. DC voltmeter: HP34401A or equivalent.
4. Oscilloscope:Tektronix TDS744A or equivalent.
Setup and Test
A: Load and Line Regulation (see connection diagram in Figure 4).
1. Apply a DC power supply and DC voltmeter across input voltage terminals VIN+ (positive terminal) and
GND (negative terminal or return).
2. Apply a DC load and DC voltmeter to output terminals. VO+ and GND.
3. Vary the load from 0A to 2.5A and the input voltage from 2.7V to 5.5V while monitoring the output voltage.
4. The output voltage as measured at the output terminals of the evaluation board should not vary by more
than ±3% of the nominal voltage.
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EV-107
AAT1155 EVAL
1MHz 2.5A Buck DC/DC Converter
B. Short-Circuit and Over-Temperature Protection
1. Raise the input voltage to 5.5V.
2. Apply a short from VO+ to GND at the evaluation board terminals.
3. Remove the short and verify that output returns to its initial value.
C. Enable Input and Power OK Output
1. Short the enable pin to GND. The output should decay to zero.
2. Remove the short applied to the enable pin. The output should recover to its initial value.
3.600V
Oscilloscope
Voltmeter
Power Supply
3.650V
0.147A
1.500V
Voltmeter
Load
0-2.5A
Figure 4: AAT1155 Connection Diagram.
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EV-107
AAT1155 EVAL
1MHz 2.5A Buck DC/DC Converter
Component Part Number
U1
U1
U1
U1
CR1
C2
C4
C1
C3
R1
R2
L1
R3
R4
Description
AAT1155IKS-1.0-T1
AAT1155IKS-1.8-T1
AAT1155IKS-2.5-T1
AAT1155IKS-3.3-T1
B340LA
594D127X96R6R3C2T
565D107X0016C
GRM319R60J106KE01
GRM155R61A104KA01
Chip Resistor
Chip Resistor
CDRH6D28-1R5
Chip Resistor
Chip Resistor
1.0V 850kHz 2.5A Buck Converter
1.8V 850kHz 2.5A Buck Converter
2.5V 850kHz 2.5A Buck Converter
3.3V 850kHz 2.5A Buck Converter
Low VF 3A 40V Schottky Diode
120µF, 6.3V, Tantalum
100µF, 16V, Tantalum
10µF, 6.3V, X5R, 10%, 1206
0.1µF, 25V, X5R, 10%, 0402
100kΩ, 5%, 1/16W, 0402
100kΩ, 5%, 1/16W, 0402
1.5µH Shielded
AAT1155IKS-1.0-T1
Table 3, 1%, 1/16W, 0402
AAT1155IKS-1.1-T1 thru
0Ω, 0402
AAT1155IKS-3.3 -T1
AAT1155IKS-1.0-T1
10kΩ, 1%, 1/16W; 0402
(when output is >1.0V only,
otherwise not needed)
AAT1155IKS-1.1-T1 thru
AAT1155IKS-3.3 -T1
Manufacturer
AnalogicTech
AnalogicTech
AnalogicTech
AnalogicTech
Diodes Inc.
Vishay
Vishay
MuRata
MuRata
Vishay
Vishay
Sumida
Vishay
Vishay
Vishay
n/a
Table 2: AAT1155 EVAL Bill of Materials.
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EV-107
AAT1155 EVAL
1MHz 2.5A Buck DC/DC Converter
Output Voltage
For an adjustable output, set R4 to 10kΩ and select R3 according to Table 3 using the AAT1155IKS-1.0-T1.
VO (V)
Ω)
R3 (kΩ
1.0
1.1
1.2
1.25
1.3
1.4
1.5
1.6
1.7
1.8
1.85
1.9
2.0
2.1
2.2
2.3
2.4
2.5
3.3
0.00 (short)
1.00
2.00
2.55
3.01
4.02
4.99
6.04
6.98
8.06
8.45
9.09
10.0
11.0
12.1
13.0
14.0
15.0
23.2
Ω).
Table 3: Resistor Selection for Adjustable Output Voltage (R4 = 10kΩ
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EV-107
AAT1155 EVAL
1MHz 2.5A Buck DC/DC Converter
EV-107.2005.01.1.0
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