Datasheet

LM5118, LM5118-Q1
SNVS566G –APRIL 2008–REVISED FEBRUARY 2013 www.ti.com
The highest power dissipating components are the two power MOSFETs, the recirculating diode, and the output
diode. The easiest way to determine the power dissipated in the MOSFETs is to measure the total conversion
losses (P
IN
- P
OUT
), then subtract the power losses in the Schottky diodes, output inductor and any snubber
resistors. An approximation for the recirculating Schottky diode loss is:
P = (1-D) x I
OUT
x V
FWD
. (31)
The boost diode loss is
P = I
OUT
x V
FWD
. (32)
If a snubber is used, the power loss can be estimated with an oscilloscope by observation of the resistor voltage
drop at both turn-on and turn-off transitions. The LM5118 package has an exposed thermal pad to aid power
dissipation. Selecting diodes with exposed pads will aid the power dissipation of the diodes as well. When
selecting the MOSFETs, pay careful attention to R
DS(ON)
at high temperature. Also, selecting MOSFETs with low
gate charge will result in lower switching losses.
Figure 26. 12V, 3A Typical Application Schematic
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