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EFFICIENCY and POWER LOSSES
Figure 15 shows the efficiency and power loss results when operating from 48 V to 12 V at various switching frequencies using a 2.2 µH inductor.
THERMAL PERFORMANCE
Figures 16 through 18 shows the thermal performance of the board when operating at 48 V delivering 12 V into the load with 1000-1500 LFM
(high) airflow.
Table 3: Measured I
DD
current (V
DD
= 5 V) (5)
Setting\Condition f
SW
= 500 kHz f
SW
= 1 MHz
Enabled (nEN = low, V
IN
= 48 V) 40 mA 58 mA
Disabled (nEN = high) 3.6 mA 5.1 mA
Figure 15: Measured efficiency and power loss operating at various switching frequencies and using L = 2.2 µH
Figure 16: Measured thermal image showing the case temperature when operating under the following conditions:
f
S
= 500 kHz, I
OUT
= 23 A output, 25°C ambient and high airflow
500 kHz
1 kHz
1.5 MHz
96.2
95.9
95.1
Ef
fic
ie
nc
y (%)
Losses (W)
I
OUT
(A)
500 kHz
1 kHz
1.5 MHz
96.5
96.0
95.5
95.0
94.5
94.0
93.5
93.0
40
35
30
25
20
15
10
5
0
0 10 20 30 40 5 15 25 35 0 10 20 30 40 5 15 25 35
I
OUT
(A)
PCB without heatsink
(5) Includes current consumption from dead-time logic circuit.