ANALOG
DEVICES
Evaluation Board for Step-Down DC-to-DC
Converter Solution
EVAL-ADP2105
FEATURES
Efficiency >95%
Input voltage range: 2.7 V to 5.5 V
Output voltage range: 0.8 V to VIN
Maximum output current: 1.0 A
Switching frequency: 1.2 MHz
Quiescent current: 20 μA
Shutdown current: 0.1 μA
Enable/shutdown logic input
Optimized for small ferrite core inductors
Optimized for tiny ceramic input and output capacitors
Programmable soft start with single capacitor
Programmable compensation for optimizing transient
performance
GENERAL DESCRIPTION
The ADP2105 evaluation board is a complete step-down dc-to-dc
converter solution using the ADP2105 step-down dc-to-dc
converter. It provides a ±1% accurate (±3% over all conditions)
regulated output voltage with load currents up to 1 A. It comes
in two versions: the ADP2105-1.8-EVAL with fixed output
voltage of 1.8 V and the ADP2105-EVAL with adjustable output
voltage initially set to 2.5 V.
The ADP2105 is a synchronous, step-down dc-to-dc converter
that uses a current-mode pulse width modulation (PWM)
control scheme at medium-to-heavy load currents for high
efficiency and smoothly transitions to a pulse frequency
modulation (PFM) mode at light loads to conserve power.
The power switch and synchronous rectifier are integrated for
minimal external part count and high efficiency. The ADP2105
is optimized for operation with small ferrite core inductors and
tiny ceramic capacitors to deliver the maximum output power
per square inch of the PCB board area.
For more details, see the ADP2105 data sheet.
FUNCTIONAL BLOCK DIAGRAM
GND
GND
ADP2105 VOUT
C2C5
C6
R1
R4
R3
R5
C7
C3
L1
C4
ENABLE
R2
J1 VIN
C1
ANALOG DEVICES, POWER MANAGEMENT (STP)
ADP2105 EVALUATION BOARD
VOUT
:
06312-001
Figure 1.
without notice. Trademarks and registered trademarks are the property of their respective owners.
Evaluation boards are not authorized to be used in life support devices or systems.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2007 Analog Devices, Inc. All rights reserved.
Rev. 0
Evaluation boards are only intended for device evaluation and not for production purposes.
Evaluation boards as supplied “as is” and without warranties of any kind, express, implied, or
statutory including, but not limited to, any implied warranty of merchantability or fitness for a
particular purpose. No license is granted by implication or otherwise under any patents or other
intellectual property by application or use of evaluation boards. Information furnished by Analog
Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result
from its use. Analog Devices reserves the right to change devices or specifications at any time
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
EVAL-ADP2105
Rev. 0 | Page 2 of 12
TABLE OF CONTENTS
Features .............................................................................................. 1
General Description......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Using the Evaluation Board............................................................. 3
Powering Up the Evaluation Board............................................ 3
Measuring Evaluation Board Performance .................................. 3
Modifying the Evaluation Board.....................................................4
Measurement Setup...........................................................................5
Typical Performance Characteristics ..............................................6
Ordering Information.......................................................................7
Bill of Materials..............................................................................7
Ordering Guide .............................................................................9
ESD Caution...................................................................................9
REVISION HISTORY
1/07—Revision 0: Initial Version
EVAL-ADP2105
Rev. 0 | Page 3 of 12
USING THE EVALUATION BOARD
POWERING UP THE EVALUATION BOARD
The ADP2105 evaluation board is supplied fully assembled and
tested. Before applying power to the evaluation board, follow
the procedures outlined in this section.
Jumper J1
Before turning on the ADP2105 evaluation board, make sure
that all the components are present, but that Jumper J1 is removed.
Input Power Source
Before connecting the power source to the ADP2105 evaluation
board, make sure it is turned off. If the input power source
includes a current meter, use that meter to monitor the input
current. Connect the positive terminal of the power source to the
VIN terminal on the evaluation board, and the negative terminal of
the power source to the GND terminal of the evaluation board. If
the power source does not include a current meter, connect a
current meter in series with the input source voltage. Connect the
positive lead (+) of the power source to the ammeter positive (+)
connection, the negative lead (−) of the power source to the GND
terminal on the evaluation board, and the negative lead (−) of the
ammeter to the VIN terminal on the board.
Output Load
Although the ADP2105 evaluation board can sustain the sudden
connection of the load, it is possible to damage the load if it is not
properly connected. Make sure the board is turned off before con-
necting the load. If the load includes an ammeter, or if the current
is not measured, connect the load directly to the evaluation board,
with the positive (+) load connection to the VOUT terminal and the
negative (−) load connection to the GND terminal. If an ammeter
is used, connect it in series with the load: connect the positive (+)
ammeter terminal to the evaluation board VOUT terminal, the nega-
tive (−) ammeter terminal to the positive (+) load terminal, and the
negative (−) load terminal to the evaluation board GND terminal.
Once the load is connected, make sure it is set to the proper
current before powering the ADP2105 evaluation board.
Input and Output Voltmeters
Measure the input and output voltages with voltmeters. Make
sure that the voltmeters are connected to the appropriate
evaluation board terminals and not to the load or power source
themselves. If the voltmeters are not connected directly to the
evaluation board, the measured voltages would be incorrect due
to the voltage drop across the leads and/or connections between
the evaluation board, the power source, and/or the load.
Connect the input voltage measuring voltmeter positive
terminal (+) to the evaluation board VIN terminal, and the
negative (−) terminal to the evaluation board GND terminal.
Connect the output voltage measuring voltmeter positive (+)
terminal to the evaluation board VOUT terminal and the negative
(−) terminal to the evaluation board GND terminal.
Turning On the Evaluation Board
Once the power source and load are connected to the ADP2105
evaluation board, the board can be powered for operation.
Slowly increase the input power source voltage until the input
voltage exceeds the minimum input operating voltage of 2.7 V.
Insert Jumper J1 and check to see if the output voltage rises to the
regulated output voltage (1.8 V for the ADP2105-1.8-EVAL and
2.5 V for the ADP2105-EVAL). If the load is not already enabled,
enable the load, and check that it is drawing the proper current and
that the output voltage maintains voltage regulation.
MEASURING EVALUATION BOARD PERFORMANCE
Measuring Output Voltage Ripple
To observe the output voltage ripple, place an oscilloscope
probe across the output capacitor (C3/C4) with the probe
ground lead at the negative (−) capacitor terminal and the
probe tip at the positive (+) capacitor terminal. Set the
oscilloscope to ac, 20 mV/division, and 2 μs/division time base.
In the PWM mode of operation, the output voltage ripple is
small (<20 mV), but in PFM mode, the output voltage ripple
can be as large as 50 mV.
Measuring the Switching Waveform
To observe the switching waveform with an oscilloscope, place
the oscilloscope probe tip at the end of the inductor that is
connected to the LX pins with the probe ground at GND. Set
the oscilloscope to dc, 2 V/division, and 2 μs/division time base.
The switching waveform must alternate between 0 V and
approximately the input voltage.
Measuring Load Regulation
The load regulation must be tested by increasing the load at
the output and looking at the change in output voltage. To
minimize voltage drop, use short low-resistance wires, especially
for heavy loads.
Measuring Line Regulation
Vary the input voltage and examine the change in the output
voltage.
Measuring Efficiency
The efficiency, η, is measured by comparing the input power
with the output power.
ININ
OUTOUT
IV
IV
×
×
=
η
Measure the input and output voltages as close as possible to the
input and output capacitors to reduce the effect of IR drops.
Measuring Inductor Current
The inductor current can be measured by removing one end of
the inductor from its pad and connecting a current loop in
series with it. Then a current probe can be used to measure the
current flowing through the current loop, as shown in Figure 2.
EVAL-ADP2105
Rev. 0 | Page 4 of 12
MODIFYING THE EVALUATION BOARD
The ADP2105 evaluation board is supplied fully assembled and
tested for proper operation. It comes in two versions: the
ADP2105-1.8-EVAL with fixed output voltage of 1.8 V and the
ADP2105-EVAL with adjustable output voltage initially set to 2.5 V.
The two most common modifications that can be done to the
evaluation boards are changing the output voltage and changing
the load transient response.
Changing the Output Voltage
The ADP2105-EVAL output regulation voltage can be changed
by altering its external components. The ADP2105-1.8-EVAL
output regulation voltage is fixed at 1.8 V and cannot be
changed.
The ADP2105-EVAL output regulation voltage is set by a resistive
voltage divider consisting of Resistors R4 and R5. Resistor R4
corresponds to the RTOP resistor in the ADP2105 data sheet, and
Resistor R5 corresponds to the RBOT resistor in the ADP2105
data sheet. The output regulation voltage is determined by the
equation
⎥
⎦
⎤
⎢
⎣
⎡+
×=
BOT
BOTTOP
OUT R
RR
VV8.0
where:
RTOP is the value of the top resistor of the voltage divider (R4).
RBOT is the value of the bottom resistor of the voltage divider (R5).
VOUT is the output regulation voltage in volts.
To set the output regulation voltage to the desired value, first
determine the value of the bottom resistor, RBOT, by
STRING
FB
BOT I
V
R=
where:
VFB = 0.8 V, the internal reference.
ISTRING is the resistor divider string current (20 μA nominally).
Once RBOT is determined, calculate the value of the top resistor,
RTOP, by
⎥
⎦
⎤
⎢
⎣
⎡−
=
FB
FBOUT
BOTTOP V
VV
RR
For example, to set the output regulation voltage of the
ADP2105-EVAL to 2.0 V, calculate the value of Resistor R4 and
Resistor R5 as shown below.
Ω=== k40
μ20
V8.0
AI
V
R5
STRING
FB
Ω=
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡−
×Ω=
⎥
⎦
⎤
⎢
⎣
⎡−
×= k60
V8.0
V8.0V2
k40
FB
FB
OUT
V
VV
R5R4
Note that when the output voltage of ADP2105-EVAL is
changed, the output capacitors (C3 and C4), inductor (L1), and
compensation components (R1 and C6) are recalculated and
changed according to the Application Information section in
the ADP2105 data sheet to ensure stable operation.
Changing the Load Transient Response
The ADP2105 evaluation board load transient response can be
altered by changing the output capacitors (C3 and C4) and
compensation components (R1 and C6) as explained in the
Output Capacitor Selection and Loop Compensation sections of
the ADP2105 data sheet. By default, the load transient response
of the ADP2105 evaluation board is set to 5% of the output
voltage for a 1 A load transient.
Consider an example where the load transient response of the
ADP2105-1.8-EVAL is changed to 10% of the output voltage for
a 1 A load transient.
First, choose the output capacitors (C3 and C4) based on the
load transient response requirements. The desired load transient
response is 10% overshoot for a 1 A load transient. For this
condition, the % Overshoot for a 1 A Load Transient Response vs.
Output Capacitor × Output Voltage figure, in the ADP2105 data
sheet, gives
Output Capacitor × Output Voltage = 25 μC
μF14
V8.1
μC25 ≈=⇒ CapacitorOutput
Next, taking into account the loss of capacitance due to dc bias
as shown in the % Drop-In Capacitance vs. DC Bias for Ceramic
Capacitors figure, in the ADP2105 data sheet, let C3 and C4 be
two 10 μF X5R MLCC capacitors (GRM21BR61A106KE19L).
Finally, calculate the compensation resistor and compensation
capacitor as shown below:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
REF
OUTOUT
CSm
CROSS
COMP V
VC
GG
F
R)π2(
8.0
Ω=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
×
=k135
V8.0
V8.1μF14
V/A875.1V/μA50
kHz80)π2(
8.0
pF60
kΩ135kHz80π
2
π
2=
××
==
COMPCROSS
COMP RF
C
Therefore, the compensation resistor is 135 kΩ and the
compensation capacitor is 68 pF.
EVAL-ADP2105
Rev. 0 | Page 5 of 12
MEASUREMENT SETUP
GND
GND
ADP2105 V
OUT
C2C5
C6
R1
R4
R3
R5
C7
C3
C4
L1
ENABLE
R2 J1 V
IN
C1
VD 1S DIV
mVVCH
VPOS
NVER T
DVADVA ADD
VD 1S DIV
mVV
1V SEP
OFF
0V H
0V V
OFF
0V H
0V V
1V SEP AT N ORW
EVE
OSCILLOSCOPE
INDUCTOR
CURRENT
WAVEFORM
LX NODE
WAVEFORM
OUTPUT
VOLTAGE
WAVEFORM
3A VOLTAGE SOURCE
V
IN
I
IN
ELECTRONIC LOAD
VOLTMETER
V
OUT
I
OUT
CURRENT
PROBE
INDUCTOR
06312-010
PROBE OUTPUT VOLTAGE
ACROSS OUTPUT CAPACITOR
Figure 2. Typical Measurement Setup
>- >-
u+L
L
Tjfl
>—>-
y‘l
«\meva
\ ‘ \
l
\ \
4
[‘4'
‘ v
é
EVAL-ADP2105
Rev. 0 | Page 6 of 12
TYPICAL PERFORMANCE CHARACTERISTICS
100
50
LOAD CURRENT (mA)
EFFICIENCY (
%
)
95
90
85
80
75
70
65
60
55
V
IN
=2.7V
V
IN
=3.6V
V
IN
=4.2V
V
IN
=5.5V INDUCTOR: SD3814, 3.3µH
DCR: 93mΩ
T
A
=25°C
1 10 100 1000
06312-004
Figure 3. Efficiency—ADP2105-1.8-EVAL (1.8 V Output)
CH1 50mV
6%CH4 200mAΩCH3 2V
M 2µs A CH3 3.88V
T
3
4
1
INDUCTOR CURRENT
OUTPUT VOLTAGE (AC-COUPLED)
LX NODE
(SWITCH NODE)
06312-005
Figure 4. PFM Mode of Operation at Light Load (10 mA)
CH2 100mV~ CH3 1ACH1 2V M 10µs A CH3 0.5A
1
3
2
LX NODE (SWITCH NODE)
OUTPUT VOLTAGE (AC-COUPLED)
OUTPUT CURRENT
OUTPUT CAPACITOR: 22µF + 22µF
INDUCTOR: SD3814, 3.3µH
COMPENSATION RESISTOR: 270kΩ
COMPENSATION CAPACITOR: 39pF
CH2 LOW
–112mV
06312-006
Figure 5. 1 A Load Transient Response for ADP2105-1.8-EVAL
50
55
60
65
70
75
80
85
90
95
100
EFFICIENCY (%)
1 10 100 1000
LOAD CURRENT (mA)
06312-007
INDUCTOR: SD3814, 3.3µH
DCR: 93mΩ
T
A
= 25°C
V
IN
= 3.0V
V
IN
= 4.2V
V
IN
= 5.5V
V
IN
= 3.6V
Figure 6. Efficiency—ADP2105-EVAL (2.5 V Output)
CH1 20mV
17.4%CH4 1AΩCH3 2V
M 1µs A CH3 3.88V
T
3
4
1
LX NODE (SWITCH NODE)
OUTPUT VOLTAGE (AC-COUPLED)
INDUCTOR CURRENT
06312-008
Figure 7. PWM Mode of Operation at Medium/Heavy Load (1 A)
3
1
2
T
CH1 2V
20.20%
CH2 100mV~
CH3 5V
M 10µs A CH3 2.60V
T
CH2 LOW
–136mV
06312-009
LX NODE (SWITCH NODE)
OUTPUT VOLTAGE (AC-COUPLED)
OUTPUT CURRENT
Figure 8. 1 A Load Transient Response for ADP2105-EVAL with VOUT Set to 2.5 V
EVAL-ADP2105
Rev. 0 | Page 7 of 12
ORDERING INFORMATION
BILL OF MATERIALS
Table 1. Bill of Materials for ADP2105-1.8-EVAL
Description
Reference
Designator
Reference
Name1Qty. Manufacturer Part Number
Capacitor, MLCC, 4.7 μF, 10 V,
0805, X5R, SMD
C1, C2 CIN1, CIN2 2 Murata GRM21BR61A475KA73L
Capacitor, MLCC, 22 μF, 6.3 V,
0805, X5R, SMD
C3, C4 COUT 2 Murata GRM21BR60J226ME39L
Capacitor, MLCC, 1 nF, 16 V,
0603, X7R, SMD
C5 CSS 1
Vishay Vitramon or
equivalent
VJ0603Y102KXJA
Capacitor, MLCC, 39 pF, 50 V,
0603, NPO
C6 CCOMP 1 Vishay Vitramon or
equivalent
VJ0603Y390KXJA
Capacitor, MLCC, 0.1 μF, 25 V,
0603, X7R, SMD
C7 IN (filter
capacitor)
1 Vishay Vitramon or
equivalent
VJ0603Y104KXXA
Resistor, 274 kΩ, 1%, 0603, SMD R1 RCOMP 1 Vishay Dale or
equivalent
CRCW06032743FRT1
Resistor, 100 kΩ, 1%, 0603, SMD R2 EN (pull
down)
1 Vishay Dale or
equivalent
CRCW06031003FRT1
Resistor, 10 Ω, 1%, 0603, SMD R3 IN (filter
resistor)
1 Vishay Dale or
equivalent
CRCW060310R0FRT1
Resistor, 0 Ω, 1%, 0603, SMD R4 1 Vishay Dale or
equivalent
CRCW06030000ZSSF
Bottom Resistor of Voltage
Divider2
R5
Inductor 3.3 μH, 3.9 mm ×
3.9 mm x 1.1 mm
L1 L 1
Coilcraft®, Toko®,
Cooper Bussmann
LLPS4012-332MLB 1098AS-
DE2812C-3.3uH,
SD3814-3.3uH
1.8 V, 1 A Step-Down DC-to-DC
Converter
U1 1 Analog Devices, Inc. ADP2105-1.8
Headers, 0.100, Single, Straight VOUT, VIN, GND,
GND, J1, EN
12 Sullins Electronics or
equivalent
S1012-36-ND PTC36SAAN
1 Refer to the Typical Applications Circuit for Fixed Output Voltage Options figure in the ADP2105 data sheet.
2 Do not solder this component onto the board.
OUTPUT VOLTAGE: 1.8V
OUT
V
CC
OUT
R5
NS
C4
22µF
C3
22µF
R4
0Ω
V
CC
06312-002
C2
4.7µF
R1
274kΩ
C6
39pF
L1
3.3µH
C1
4.7µF
V
OUT
C5
1nF
2
GND
INPUT VOLTAGE: 2.7V TO 5.5V
R3
10Ω
V
IN
GND
SS
LX2
AGND PADDLECOMP
PGND
NC
OUT_SENSE PWIN1IN1GND4
LX1
PWIN2
12
11
10
9
16 15 14 13
5 6 7 17 8
EN
GND3
GND2
GND1
V
CC
R2
100kΩ
EN
J1
NC = NO CONNECT
1
U1
ADP2105-1.8
C7
0.1µF
1
2
3
4
Figure 9. Evaluation Board Schematic of ADP2105-1.8-EVAL with VOUT = 1.8 V
EVAL-ADP2105
Rev. 0 | Page 8 of 12
Table 2. Bill of Materials for ADP2105-EVAL with VOUT Set to 2.5 V
Description
Reference
Designator
Reference
Name1 Qty. Manufacturer Part Number
Capacitor, MLCC, 4.7 μF, 10 V,
0805, X5R, SMD
C1, C2 CIN1, CIN2 2 Murata GRM21BR61A475KA73L
Capacitor, MLCC, 22 μF, 6.3 V,
0805, X5R, SMD
C3 COUT 1 Murata GRM21BR60J226ME39L
Capacitor, MLCC, 10 μF, 10 V,
0805, X5R, SMD
C4 COUT 1 Murata GRM21BR61A106KE19L
Capacitor, MLCC, 1 nF, 16 V,
0603, X7R, SMD
C5 CSS 1
Vishay Vitramon or
equivalent
VJ0603Y102KXJA
Capacitor, MLCC, 39 pF, 50 V,
0603, NPO
C6 CCOMP 1
Vishay Vitramon or
equivalent
VJ0603Y390KXJA
Capacitor, MLCC, 0.1 μF, 25 V,
0603, X7R, SMD
C7 IN (filter
capacitor)
1 Vishay Vitramon or
equivalent
VJ0603Y104KXXA
Resistor, 274 kΩ, 1%, 0603, SMD R1 RCOMP 1 Vishay Dale or equivalent CRCW06032743FRT1
Resistor, 100 kΩ, 1%, 0603, SMD R2 EN (pull
down)
1 Vishay Dale or equivalent CRCW06031003FRT1
Resistor, 10 Ω, 1%, 0603, SMD R3 IN (filter
resistor)
1 Vishay Dale or equivalent CRCW060310R0FRT1
Resistor, 87.6 kΩ, 0.5%, 0603,
SMD
R4 RTOP 1 Vishay Dale or equivalent TNPW060387K6DHTA
Resistor, 41.2 kΩ, 0.1%, 0603,
SMD
R5 RBOT 1 Vishay Dale or equivalent TNPW060341K2BEEN
Inductor 3.3 μH, 3.9 mm ×
3.9 mm x 1.1 mm
L1 L 1
Coilcraft, Toko,
Cooper Bussmann
LLPS4012-332MLB 1098AS-
DE2812C-3.3uH
SD3814-3.3uH
1 A Step-Down DC-to-DC
Converter with Adjustable
Output
U1 1 Analog Devices ADP2105-ADJ
Headers, 0.100, Single, Straight VOUT, VIN, GND,
GND, J1, EN
6
Sullins Electronics or
equivalent
S1012-36-ND PTC36SAAN
1 Refer to the Typical Applications Circuit for Adjustable Output Voltage Options figure in the ADP2105 data sheet.
OUTPUT VOLTAGE: 2.5V
R5
41.2kΩ
FB
FB
V
IN
V
CC
06312-003
C2
4.7µF
R1
274kΩ
C6
39pF
L1
3.3µH
C4
10µF
C3
22µF
C1
4.7µF
V
OUT
C5
1nF
2
GND
INPUT VOLTAGE: 2.7V TO 5.5V
R3
10Ω
V
IN
GND
SS
LX2
AGND PADDLECOMP
PGND
NC
PWIN1IN1GND4
LX1
PWIN2
12
11
10
9
16 15 14 13
5 6 7 17 8
EN
GND3
GND2
GND1
V
CC
R2
100kΩ
EN
J1
NC = NO CONNECT
1
U1
ADP2105-ADJ
R4
87.6kΩ
C7
0.1µF
1
2
3
4
FB
Figure 10. Evaluation Board Schematic for ADP2105-EVAL with Adjustable VOUT Initially Set to 2.5 V
Am
ESD (elenrosmie diszharge) sen ' ve device.
Charged device: and (mm boards (an dwxchavge
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EVAL-ADP2105
Rev. 0 | Page 9 of 12
ORDERING GUIDE
Model Description
ADP2105-1.8-EVAL Evaluation board with fixed output voltage
ADP2105-EVAL Evaluation board with adjustable output voltage
ESD CAUTION
EVAL-ADP2105
Rev. 0 | Page 10 of 12
NOTES
EVAL-ADP2105
Rev. 0 | Page 11 of 12
NOTES
ANALOG
DEVICES
www.ana|ng.nnm
EVAL-ADP2105
Rev. 0 | Page 12 of 12
NOTES
©2007 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
EB06312-0-1/07(0)
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