ISL6559EVAL1 Intersil, ISL6559EVAL1 Datasheet - Page 2

• Manufacturer Part Number: ISL6559EVAL1
• Description: EVALUATION BOARD ISL6559
• Manufacturer: Intersil

Specifications of ISL6559EVAL1

• Main Purpose: Special Purpose DC/DC, VRM Supply
• Outputs And Type: 1, Non-Isolated
• Power - Output: 125W
• Voltage - Output: 1.25V
• Current - Output: 100A
• Voltage - Input: 5V, 12V
• Regulator Topology: Buck
• Frequency - Switching: 600kHz
• Board Type: Fully Populated
• Utilized Ic / Part: ISL6559, ISL6605
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Power Output Connections
The ISL6559EVAL1 output can be exercised using either
resistive or electronic loads. Copper alloy terminal lugs
provide connection points for loading. Tie the positive load
connection to VCORE, terminal J2 or J3, and the negative to
ground, terminal J4 and J10. A shielded scope probe test
point, J8, allows for inspection of the output voltage,
VCORE.
Enabling the Controller
The state of VCC, EN, and FS/DIS dictate the beginning of a
soft-start interval. The FS/DIS pin is used to set the per
phase switching frequency on the evaluation board. Once
the input and output terminal connections are made, remove
the shunt across the jumper (J11) pins 3, 4 labeled OUT_EN
if installed. The EN signal is released to rise above the
ENABLE threshold of 1.23V nominal. Once the ENABLE
threshold is exceeded, a soft-start interval is initiated. The
output voltage will ramp in a controlled manner.
A resistor divider from the +12V input is connected to EN on
the controller and the drivers to insure that the drivers and
controller come up at the same time.
On-Board Load Transient Generator
Most bench-top electronic loads are not capable of
producing the current slew rates required to emulate modern
microprocessors. For this reason, a discrete transient load
generator is provided on the VRM test board for evaluation.
The VRM test board is designed to work in conjunction with
the ISL6559 eval board. The VRM test board schematic is
located in later pages of this application note. In addition to
the transient load generator, the board consists of a card
edge connector (J1), pull up resistors for the VID pins, and
scope probes as well as turrets for monitoring the input and
output voltage. This board comes configured with an all
ceramic output filter, but you have the option to add Oscon
or larger ceramic capacitors.
The on board transient circuit can be modified to operate at
different frequencies or have different load steps. As
received the on-board transient is designed to operate at
33Hz. The current step is dependent on the di/dt of the
transient load which is dependent on the output voltage and
the number of switches being used as seen in Figure 1.
Where:
• di/dt = V
• di/dt is the transient slew rate
• N is the number of switches
• t
• R
• V
rise
OUT
EQ
is the rise time
is the equivalent resistance
is the output voltage
out
x N/ (t
rise
x R
EQ
2
)
Application Note 1132
(EQ. 1)
The load step can be verified by measuring the voltage at J7
of the test board. Once you have that value you can
calculate your current step. The di/dt can be verified by
measuring the rise time of the load step. Rise time is
measured from 10% and 90% of the transient voltage. Plug
that value into equation 1 to calculate the di/dt. The rise time
can be improved by switching to thin film resistors from the
wire wound resistors.
The low frequency transient is running at 33Hz but can be
modified to run faster by simply adjusting the values of R6,
R7 and C80. Frequency can be increased by decreasing the
value of C80 (currently 10µF). If you want to change the duty
cycle, ON time is proportional to R7 (402Ω) and the OFF
time is proportional to R6 (46.7kΩ). It may be necessary to
decrease the ON time at high frequency. If the duty cycle is
too high, the switching transistor and sense resistors will
overheat. Do not use less than 10Ω for R7 or the max pulsed
current in Q1 will exceed its rating.
The load resistor values are 120mΩ stacked 3 high that
gives effectively 40mΩ, the r
Thus, the equivalent resistance for each switch is 56mΩ.
.
900
800
700
600
500
400
300
200
100
FIGURE 1. PLOT OF TRANSIENT LOAD CIRCUIT
0
0.80
0.90
1.00
N = 4
N = 3
N = 2
N = 1
1.10
DS(ON)
V
OUT
1.20
(V)
of the FETs is 16mΩ.
1.30
1.40
1.50
1.60