ISL6551EVAL1 Intersil, ISL6551EVAL1 Datasheet - Page 32

• Manufacturer Part Number: ISL6551EVAL1
• Description: EVALUATION BOARD ISL6551
• Manufacturer: Intersil

Specifications of ISL6551EVAL1

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Isolated
• Voltage - Output: 3.3V
• Current - Output: 60A
• Voltage - Input: 36 ~ 75V
• Regulator Topology: Buck
• Frequency - Switching: 470kHz
• Board Type: Fully Populated
• Utilized Ic / Part: ISL6551
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

As shown in the figures above, the current transformer and
the main transformer are the hottest components. Without
any airflow, their case temperatures would rise significantly
and exceed the device ratings at heavy load operations.
Users should do a more thorough analysis at the worst case
operating condition to evaluate thermal stress of each
device. The current transformer is roughly measured to be
above 130°C at room ambient temperature, 48V input and
3.3V, 50A output without any airflow due to its heavy glossy
pinout, so it is recommended that users redesign the current
sense transformer for a better form factor and thermal
performance.
Current Share
Two equal length (3 inch) and size (10 AWG) wires split the
load into each individual converter, thus, the impedance
mismatching of current-carrying traces from the converters
to the load is minimized. The current delivered by each
converter is measured with only one current probe to reduce
measurement error. With this kind of setup and
measurement method, impedance difference and
measurement error are still greater than that of building both
converters in a board with a symmetric layout and measuring
the current with precise current sense resistors. The
measurement error increases with decreasing load.
Figure 60 shows current share curves at various input lines
and output voltages. The current sharing is inversely
proportional to the load, and the slave unit can share the
load within 5% of the master unit at full load operation. Since
the offset of the error amplifier and the difference of the
output reference as well as the difference of power train
components between both units remains constant, the
difference of the load currents delivered by the master and
the slave units almost remains constant, as shown in Figure
61. In addition, at no-load operation, the master unit will
source current into the slave units because the higher
voltage (master) back drives the lower voltage (slave).
FIGURE 59. OUTPUT INDUCTOR (L2) CASE TEMPERATURE
55
50
45
40
35
45
Input Voltage (V)
55
32
65
75
Application Note 1002
2.64V
3.3V
3.63V
FIGURE 62. TURN ON SLAVE (CHANNEL 3 AND CHANNEL 2)
FIGURE 61. CURRENT OF MASTER AND SLAVE UNIT
45
40
35
30
25
20
15
10
35
30
25
20
15
10
5
0
5
0
0
5 10 15 20 25 30 35 40 45 50 55 60
FIGURE 60. CURRENT SHARE CURVES
5 10 15 20 25 30 35 40 45 50 55 60
FIRST. MASTER: CHANNEL 4 AND CHANNEL 1
Load Current (A)
2
1
4
Load Current (A)
3
48V-3.3VM
48V-3.3VS
75V-2.64VM
75V-2.64VS
36V-3.63VM
36V-3.63VS
48V-3.3V
75V-2.64V
36V-3.63V