Application Note 1793
3. Make sure that the setup is connected correctly. Turn on the
wire/jumper connections in this case). Measure the output
voltages, VOUT1, which should be at 1.2V.
power supply. If the board is working properly, the green LED
will illuminate; if not, the red LED will illuminate (recheck the
wire/jumper connections in this case). Measure the output
voltages, VOUT1, which should be at 1.2V and VOUT2, which
should be at 1.5V
6. Apply any load that is less than 30A for normal steady state
operation. Refer to Table 1 to change the output voltage by
changing resistor R2.
TABLE 2. BOARD CONFIGURATION FOR SINGLE OUTPUT 30A
APPLICATION
4. If different output voltages are desired, board resistors can be
exchanged to provide the desired VOUT. Please refer to Table 1
for R2/R4 resistor values, which can be used to produce
different output voltages.
ENC
OPEN OPEN
ON ON
VMON MODE COMP
R9
0
R13
0
R14
OPEN
0
Dual
OPEN
ON
OPEN
ON
For 12V VIN and VOUT more than 1.5V, the switching frequency
will need to be adjusted, as shown in Table 1. The resistor RFSET
can be adjusted for the desired frequency. No frequency
adjustments are necessary for VOUT below 1.5V. For 5V VIN, the
frequency does not need to be adjusted and the module default
frequency can be used at any allowed VOUT. If the output voltage
is set to more than 1.8V, the output current will need to be
derated to allow for safe operation. Please refer to the derating
curves in the ISL8225M datasheet.
Single
OPEN OPEN
Optional Cascadable Mode
Cascadable mode is needed when multiple evaluation boards
are used for paralleling or multiple output use. To demo the
parallel features, it is recommended to use ISL8225MEVAL2Z
6-phase evaluation board for an easy and efficient setup (see
AN1789). Otherwise, follow the steps shown below:
TABLE 1. VALUE OF BOTTOM RESISTOR (TOP RESISTOR R1,
R3 = 1kΩ) AND FREQUENCY SELECTION FOR DIFFERENT
OUTPUT VOLTAGES
1. In order to generate CLKOUT at a shifted phase clock signal,
the control loop of VOUT2 needs to be disabled by connecting
VSEN2- to VCC.
VOUT
(V)
R2 /R4
(Ω)
FREQUENCY
(kHz)
RFSET (Ω)
(VIN = 12V)
2. Program MODE and VSEN2+ pin voltages to set the CLKOUT
signal and the shifted degrees between two phases on the
board (refer to Table 3).
1.0
1.2
1.5
2.5
3.3
5.0
5.5
1500
1000
665
316
DEFAULT
DEFAULT
DEFAULT
650
OPEN
OPEN
OPEN
249k
124k
82.5k
82.5k
3. Use a coaxial cable to connect CLKOUT (J5) to SYNC (J2) of the
next evaluation board, which can be programed for parallel or
dual output use.
4. If the second board is programed for parallel use, the ISHARE
pins of the first and second boards need to be tied together.
Using two twisted wires, short two different jumpers of JP7
(ISHARE/SGND) on two evaluation boards. Add 1nF
221
800
137
950
121
950
capacitors of C14 for different boards to decouple the noise.
5. If the third board is used in cascadable mode, the second
board can only be used in the parallel mode to generate the
CLKOUT signal for the SYNC pin on the third board.
Optional Paralleled Single Output Mode
1. To set up the parallel mode, short JP1 (ENC), JP2 (VMON) and
JP3 (COMP) with a jumper. To set up 180° interleaving phase
between 2 channels, short the MODE pin and GND pin of JP6
with a jumper.
6. Follow the instructions from Steps 1 through 5 for more
cascadable boards.
2. Remove R9 and R13. Change R14 to 0Ω. Change R18 and
R19 to 0Ω. Short VOUT1 to VOUT2 using short wires or copper
straps. Add C2 for a 470pF capacitor.
Evaluation Board Information
The evaluation board size is 114.3mm x 76.2mm. It is a 4-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 dual 15A reference design. Refer to “Layout” on page 6. The
board is made of FR4 material and all components, including the
solder attachment, are lead-free.
3. Connect a power supply capable of sourcing at least 5A to the
inputs BA7 (VIN1), BA8 (GND), BA3 (VIN2) and BA4 (GND) of
the ISL8225MEVAL4Z evaluation board, with a voltage
between 4.5V to 20V. VIN1 and VIN2 need to be shorted
together.
4. Connect an electronic load or the device to be powered to the
outputs BA5 (VOUT1) and BA6 (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.
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 designed carefully to maximize thermal performance. To
achieve this, select enough trace width, copper weight and the
proper connectors.
5. Make sure the setup is connected correctly prior to applying any
power to the board. Adjust the power supply to 12V and turn on
the input power supply. If the board is working properly, the green
LED will illuminate; if not, the red LED will illuminate (recheck the
This evaluation board is designed for running dual 15A at room
temperature without additional cooling systems needed.
AN1793.1
December 6, 2012
2
