DC1297B Linear Technology, DC1297B Datasheet - Page 17

• Manufacturer Part Number: DC1297B
• Description: BOARD EVAL LTM4612
• Manufacturer: Linear Technology
• Series: µModuler

Specifications of DC1297B

• Design Resources: LTM4612 Spice Model LTM4612 Gerber Files DC1297B Design Files DC1297B Schematic
• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Power - Output: -
• Voltage - Output: 3.3V, 5V ,12V
• Current - Output: 5A
• Voltage - Input: 5 ~ 36 V
• Regulator Topology: Buck
• Frequency - Switching: 850kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LTM4612
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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:
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.
R
FB
=
Figure 8. Radiated Emission Scan with 24V
5V
OUT
V
0.6V
–10
40
70
60
50
30
20
10
OUT
100k
0
30
N
at 5A Measured in 10 Meter Chamber
128.1
− 1
226.2
324.3
FREQUENCY (MHz)
422.4
EN55022 CLASS B LIMIT
520.5
618.6
716.7
814.8
912.9
4612 F08
1010
IN
to
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
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
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
proximate θ
of the thermal characteristics is provided in the thermal
application note, AN110.
JA
of the condition. Each figure has three curves that are
JA
for Figures 11 to 16. A complete explanation
JA
. Table 3 provides the ap-
LTM4612
17
JA
4612fb
for