LTM4612
17
4612fc
For more information
Figure 8. Radiated Emission Scan with 24V
IN
to
5V
OUT
at 5A Measured in 10 Meter Chamber
FREQUENCY (MHz)
30
dBµV/m
30
70
128.1
226.2
324.3
10
60
20
0
–10
50
40
422.4
520.5
618.6
716.7
814.8
912.9
1010
EN55022 CLASS B LIMIT
4612 F08
APPLICATIONS INFORMATION
Parallel Operation
The LTM4612 device is an inherently current mode con-
trolled device. This allows the paralleled modules to have
very good current sharing and balanced thermal on the
design. Figure 21 shows a schematic of the parallel design.
The voltage feedback equation changes with the variable
N as modules are paralleled. The equation:
R
FB
=
100k
N
V
OUT
0.6V
−
1
N is the number of paralleled modules.
Radiated EMI Noise
High radiated EMI noise is a disadvantage for switching
regulators by nature. Fast switching turn-on and turn-off
make the large di/dt change in the converters, which act
as the radiation sources in most systems. LTM4612 inte-
grates the feature to minimize the radiated EMI noise to
meet the most applications with low noise requirements.
An optimized gate driver for the MOSFET and a noise
cancellation network are installed inside the LTM4612
to achieve the low radiated EMI noise. Figure 8 shows a
typical example for the LTM4612 to meet the Class B of
EN55022 radiated emission limit.
Thermal Considerations and Output Current Derating
In different applications, LTM4612 operates in a variety
of thermal environments. The maximum output current is
limited by the environment thermal condition. Sufficient
cooling should be provided to help ensure reliable opera-
tion. When the cooling is limited, proper output current
derating is necessary, considering ambient temperature,
airflow, input/output condition, and the need for increased
reliability.
The power loss curves in Figures 9 and 10 can be used
in coordination with the load current derating curves in
Figures 11 to 16 for calculating an approximate
θ
JA
for
the module. Graph designation delineates between no
heat sink, and a BGA heat sink. Each of the load current
derating curves will lower the maximum load current as a
function of the increased ambient temperature to keep the
maximum junction temperature of the power module at
125°C maximum. This will maintain the maximum operat-
ing temperature below 125°C. Each of the derating curves
and the power loss curve that corresponds to the correct
output voltage can be used to solve for the approximate
θ
JA
of the condition. Each figure has three curves that are
taken at three different air flow conditions. Each of the
derating curves in Figures 11 to 16 can be used with the
appropriate power loss curve in either Figure 9 or Figure
10 to derive an approximate
θ
JA
. Table 3 provides the ap-
proximate
θ
JA
for Figures 11 to 16. A complete explanation
of the thermal characteristics is provided in the thermal
application note, AN110.
