an1923

Application Note 1923
ISL8240MEVAL3Z 40A, Single Output Evaluation Board
Setup Procedure
Description
Board Features
The ISL8240M is a complete, dual step-down switching mode
DC/DC module. The dual outputs can easily be paralleled for
single-output, high-current use. It is easy to apply this
high-power, current-sharing DC/DC power module to
power-hungry datacom, telecom, and FPGA applications. All
that is needed in order to have a complete, 40A design ready
for use are the ISL8240M, a few passive components, and
VOUT setting resistors.
• Small, compact, and simple design
The ease of use virtually eliminates design and manufacturing
risks while dramatically improving time to market.
• Resistor programmable output voltage range from 0.6V to
2.5V (default 1.0V)
The simplicity of the ISL8240M is its off-the-shelf, unassisted
implementation. Patented module structure allows for higher
power density and better efficiency than competing solutions.
Patented current sharing in multi-phase operation greatly
reduces ripple currents, BOM costs, and complexity.
• 20A output current if VOUT is below 1.5V (output current may
need to be derated for certain conditions if VOUT is 1.5V or
above 1.5V)
The ISL8240MEVAL3Z evaluation board enables a single
output by paralleling two phases to deliver 40A continuous
load current. To evaluate the dual output configuration of the
ISL8240M, please refer to application note
AN1922, “ISL8240MEVAL4Z Dual 20A/Optional 40A
Cascadable Evaluation Board Setup Procedure.” The
ISL8240M supports input voltage from 4.5V to 20V and the
output voltage ranges from 0.6V to 2.5V. With the single
resistor modification, the output voltage can be easily adjusted
to different voltages.
• Connectors, test points, and jumpers for easy probing
Specifications
This evaluation board is designed to operate at the following
operating conditions:
• Input voltage range from 4.5V to 20V
• Switching frequency range from 350kHz to 700kHz (500kHz
by default)
• Operating temperature range: -40°C to +85°C
Recommended Equipment
• 0V to 20V power supply with at least 10A source current
capability
• Electronic load capable of sinking current up to 40A
• Digital Multimeters (DMMs)
• 100MHz quad-trace oscilloscope
Related Resources
• ISL8240M datasheet.
+
VIN V
-
+
-
LOAD
(0A~40A)
4.5V TO 20V
+
VOUT
V
-
FIGURE 1. ISL8240MEVAL3Z BOARD IMAGE
January 28, 2016
AN1923.1
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries.
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Application Note 1923
Quick Start
The inputs are J1 (VIN) and J2 (GND). The outputs are J3 (VOUT)
and J4 (GND). Refer to Figure 1 for connections.
1. Connect a power supply capable of sourcing at least 10A to
the input J1 (VIN) and J2 (GND) of the ISL8240MEVAL3Z
evaluation board, with a voltage between 4.5V to 20V.
Connect an electronic load or the device to be powered to the
output J3 (VOUT) and J4 (GND) of the board. All connections,
especially the low voltage, high current VOUT lines, should be
able to carry the desired load current and should be made as
short as possible.
2. Turn on the power supply. Measure the output voltage, VOUT,
which should be at 1.0V if the board is working properly.
3. The ISL8240MEVAL3Z is manufactured with a default VOUT
value of 1.0V; if different output voltages are desired, board
resistors can be changed to provide the desired VOUT. Please
refer to the table printed on the backside of the evaluation
board or Table 1 for RVSET resistor values, which can be used
to produce different output voltages
The switching frequency is set to 500kHz by default. For VOUT
higher than 1.0V, the switching frequency will need to be
adjusted as shown in Table 1. If the output voltage is set to 1.5V
or higher than 1.5V, the output current will need to be derated to
allow for safe operation at elevated ambient temperatures.
Please refer to the derating curves in the ISL8240M datasheet.
For VIN <5.5V, please tie VIN directly to VCC for best efficiency.
Also, it is preferred that the EN/FF voltage be higher than 1.5V in
order to achieve better stability.
TABLE 1. RESISTANCE SETTING FOR DIFFERENT OUTPUT VOLTAGES
AND OPERATING FREQUENCY (R3 = 1k)
VOUT
(V)
RVSET
(Ω)
FREQUENCY
(kHz)
RFSET
(kΩ)
1.0
Default (1500)
Default (500)
Default (237)
1.2
1000
550
174
1.5
665
600
140
1.8
499
650
115
2.5
316
700
100
This evaluation board is designed for running 40A, 1.0V at room
temperature without additional cooling systems needed.
However, if the output voltage is increased or the board is
operated at elevated temperatures, then the available current
needs to be derated. Refer to the current derating curves in the
ISL8240M datasheet to determine the output current available.
For layout of designs using the ISL8240M, the thermal
performance can be improved by adhering to the following
design tips:
1. Use the top and bottom layers to carry the large current.
VOUT1, VOUT2, Phase 1, Phase 2, PGND, VIN1 and VIN2
should have large, solid planes. Place enough thermal vias to
connect the power planes in different layers under and
around the module.
2. Phase 1 and Phase 2 pads are switching nodes that generate
switching noise. Keep these pads under the module. For
noise-sensitive applications, it is recommended to keep
phase pads only on the top and inner layers of the PCB; do not
place phase pads exposed to the outside on the bottom layer
of the PCB. To improve the thermal performance, the phase
pads can be extended in the inner layer, as shown in Phase 1
and Phase 2 pads on layers 4 and 5 (see Figures 7 and 8) for
this 40A evaluation board. Make sure that layers 3 and 6 have
the GND layers to cover the extended areas of phase pads on
layers 4 and 5 to avoid noise coupling.
3. To avoid noise coupling, we recommend adding 470pF
capacitors on all COMP pins of each module for multiple
module operations.
4. If the ambient temperature is high or the board space is
limited, airflow is needed to dissipate more heat from the
modules. A heat sink can also be applied to the top side of the
module to further improve the thermal performance (heat
sink recommendation: Aavid Thermalloy, part number
375424B00034G, www.aavid.com).
Evaluation Board Information
The evaluation board size is 3 inchx3 inch. It is a 6-layer board,
containing 2-ounce copper on the top and bottom layers and
1-ounce copper on all internal layers. The board can be used as a
40A reference design, refer to “Layout” on page 4. The board is
made up of FR4 material and all components, including the
solder attachment, are lead-free.
Thermal Considerations and Current Derating
For high current applications, board layout is very critical in order
to make the module operate safely and deliver maximum
allowable power. To carry large currents, the board layout needs
to be carefully designed to maximize thermal performance. To
achieve this, select enough trace width, copper weight and the
proper connectors.
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AN1923.1
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VCC
SYNC
TP3
ISL8240M
237k
RFSET
TP4
C6
SINGLE OUTPUT DUAL PHASE 40A
4.7µF
1.5k
20
19
18
17
16
15
14
13
470pF
C8
6.04k
R1
EN
S1
2.05k
R2
C7
1000pF
SGND
TP9
S1
FIGURE 2. ISL8240MEVAL3Z BOARD SCHEMATIC
100µF
GND
E
TP8
330µF
C17
COMP1
VMON1
1k
RVSET
100µF
C15
22
21
C9
OPEN
R3
100µF
C14
23
1.0V AT 40A
VOUT
J3
100µF
C13
24
TP6
TP10
25
100µF
C12
R4
PHASE2
PGOOD
C10
VSEN1ISHARE
CLKOUT
VIN1
EN/FF2
PGND
EN/FF1
E
VSEN1+
1
26
VCC
IN
47µF
C11
12
PGOOD
VOUT1
PHASE1
VOUT2
ISL8240MIRZ
N/C
S1
TP7
E
J4
Application Note 1923
COMP2
MODE
VMON2
SYNC
SGND
U1
SGND
TP5
3.3k
C16
22µF
22µF
C18
22µF
C5
22µF
C3
C1
2
3
4
5
6
7
VCC
VSEN2+
PHASE1
S1
SGND
VIN2
VSEN2-
10
11
GND_S1 EGND
8
E
PGND
PHASE2
TP2
9
GND
J2
E
470pF
S1
VIN
470µF
C2
3
J1
E
TP1
4.5V TO 20V
22µF
C4
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ISL8240MEVAL3Z Board Schematic
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Application Note 1923
Layout
FIGURE 3. SILKSCREEN TOP
FIGURE 4. TOP LAYER COMPONENT
FIGURE 5. LAYER 2
FIGURE 6. LAYER 3
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Application Note 1923
Layout
(Continued)
FIGURE 7. LAYER 4
FIGURE 9. BOTTOM LAYER SOLDER SIDE
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FIGURE 8. LAYER 5
FIGURE 10. SILKSCREEN BOTTOM
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Bill of Materials
MANUFACTURER
PART NUMBER
QTY.
VALUE
TOL. VOLTAGE POWER
108-0740-001
J1-J4
4
10TPB330M
C15
1
TP1-TP10
10
C1
1
470µF
20%
25V
C2-C5
4
22µF
10%
C7
1
1000pF 10%
C8, C16
2
470pF
H1045-00475-6R3V10-T
C6
1
H1045-OPEN
C9
H1046-00476-6R3V20-T
H1065-00107-6R3V20-T
PACKAGE
TYPE
JEDEC TYPE
MANUFACTURER
DESCRIPTION
CONN
BAN-JACK
Johnson
Components
Standard type banana jack
SMD
CAP_7343_149
SANYO-POSCAP
Standard solid electrolytic chip tantalum SMD
capacitor
MTP500X
Keystone
Miniature white test point 0.100 pad 0.040 Thole
SMD
CAPAE_393X402
Panasonic
Aluminum electrolytic S series type V capacitor
(RoHS compliant)
25V
1210
CAP_1210
Murata
Ceramic chip capacitor
50V
603
CAP_0603
Generic
Multilayer capacitor
10%
50V
603
CAP_0603
Generic
Multilayer capacitor
4.7µF
10%
6.3V
603
CAP_0603
Generic
Multilayer capacitor
1
OPEN
5%
OPEN
603
CAP_0603
Generic
Multilayer capacitor
C10
1
47µF
20%
6.3V
805
CAP_0805
Generic
Multilayer capacitor
C12-C14
3
100µF
20%
6.3V
1206
CAP_1206
Generic
Multilayer capacitor
C11
1
OPEN
5%
OPEN
1206
CAP_1206
Generic
Multilayer capacitor
RFSET
1
237kΩ
1%
1/16W
603
RES_0603
Generic
Thick filmchip resistor
R2
1
2.05kΩ
1%
1/10W
603
RES_0603
Generic
Thick filmchip resistor
H2511-01001-1/16W1
R3, RVSET
2
1kΩ
1%
1/16W
603
RES_0603
Generic
Thick filmchip resistor
H2511-03301-1/16W5
R4
1
3.3kΩ
5%
1/16W
603
RES_0603
Generic
Thick filmchip resistor
H2511-06041-1/16W1
R1
1
6.04kΩ
1%
1/10W
603
RES_0603
Generic
Thick filmchip resistor
ISL8240MIRZ
M1
1
QFN
QFN26_670X670_ISL8240M Intersil
5002
6
EEE1EA471P
GRM32ER71E226KE15L
H1045-00102-50V10-T
H1045-00471-50V10
H1065-OPEN
H2511-02373-1/16W1
H2511-02051-1/10W1-T
330µF
20%
10V
THOLE
Dual 20A DC/DC power module
NOTE: Resistance accuracy of feedback resistor divider R1/R2 can affect the output accuracy. Please use high accuracy resistance (i.e. 0.5% or 0.1%) to meet the output accuracy requirement.
Application Note 1923
REF DES
AN1923.1
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Application Note 1923
ISL8240MEVAL3Z Performance
Test conditions at +25°C and no air flow.
95
EFFICIENCY (%)
90
85
12VIN 1.5VOUT
100MV/DIV
12VIN 1.2VOUT
80
12VIN 1.8VOUT
12VIN 1VOUT
75
70
12VIN 2.5VOUT
65
0
5
10
15
20
25
30
35
40
100ΜS/DIV
LOAD CURRENT (A)
FIGURE 11. EFFICIENCY CURVES FOR 12V INPUT
FIGURE 12. 1VOUT TRANSIENT RESPONSE, IOUT = 0A TO 20A,
fSW = 350kHz, LOAD CURRENT SLEW RATE: 10A/µs
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is
cautioned to verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
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