ISL6551EVAL1 Intersil, ISL6551EVAL1 Datasheet - Page 29

• 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: -

THERMAL DATA
The thermal data are taken with a Fluke 80T-IR Infrared
Temperature Probe at 21
PAPST-MOTOREN TYP 4600 fan (estimated around 400
LFM or more) is placed vertically 2.0” away from the input
end of the converter. The data are used only for a relative
comparison purpose, therefore, users should not do any
thermal derating based on these thermal curves because
the data points are not necessarily presenting the absolute
values at the operating condition.
The data points in Figures 46 to 52 are taken at
Figure 46 shows the upper FET (Q14) case temperature.
The higher the input voltage is, the longer the freewheeling
period is, therefore, the higher the conduction losses of the
upper FET is. Thus, the case temperature is higher at the
high line.
FIGURE 44. EFFICIENCY CURVES FOR
FIGURE 45. EFFICIENCY AT 60A FOR
90
89
88
87
86
85
84
92
90
88
86
84
82
80
78
76
74
72
70
68
66
64
2.6
0 5 10 15 20 25 30 35 40 45 50 55 60
V
DIFFERENT V
OUT
2.8
=3.64V @~400 LFM
3
0
Iout (A)
C ambient temperature while a
Vout (V)
OUT
29
3.2
@~400 LFM
3.4
3.6
V
Application Note 1002
3.8
OUT
=3.3V.
36V
48V
75V
36V
48V
75V
Figure 47 shows the case temperature of the lower FET
(Q17). The higher the input voltage is, the higher the
switching losses of the lower FET are. At the high line, the
case temperature of the FET rises significantly since ZVS
transitions are completely lost and the switching losses
dominate the channel conduction losses.
Figure 48 shows the case temperature of the current sense
transformer (T4). At low line, the case temperature is much
higher since the current ramp through the current sense
transformer has a larger duty cycle and produces a higher
RMS value and higher resistive losses.
Figures 49 and Figure 50 show the case temperature of the
main transformer (T2) and a synchronous FET (Q1),
respectively.
Figure 51 shows the synchronous driver (M2) case
temperature. The curves in this figure look flatter than those
in other figures since the driver losses heavily depend on the
gate charge of the synchronous FETs (which remains almost
constant), rather than the output load.
Figure 52 shows the case temperature of an output inductor
(L2). At the high line, the inductor gets hotter since the ripple
current as well as its RMS value is higher.
The data points in Figures 53 to Figure 59 are taken at
various output and full load operating conditions with around
400 LFM airflow. As shown in these figures, the worst
operating point is at the high line and maximum output
voltage for all cases except the current sense transformer
(T4), which has its worst operating point at the low line and
maximum output voltage.
FIGURE 46. UPPER FET (Q14) CASE TEMPERATURE
60
55
50
45
40
35
30
25
20
20
25
30
Output Load (A)
35
40
45
50
55
60
36V
48V
75V