Datasheet

LTM4613
16
4613f
APPLICATIONS INFORMATION
low level below 0.3V. During the start-up of the regulator,
the phase-locked loop function is disabled.
INTV
CC
and DRV
CC
Connection
An internal low dropout regulator produces an internal
5V supply that powers the control circuitry and DRV
CC
for driving the internal power MOSFETs. Therefore, if
the system does not have a 5V power rail, the LTM4613
can be directly powered by V
IN
. The gate driver current
through the LDO is about 20mA. The internal LDO power
dissipation can be calculated as:
P
LDO_LOSS
= 20mA • (V
IN
– 5V)
The LTM4613 also provides the external gate driver voltage
pin DRV
CC
. If there is a 5V rail in the system, it is recom-
mended to connect the DRV
CC
pin to the external 5V rail.
This is especially true for higher input voltages. Do not
apply more than 6V to the DRV
CC
pin.
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. LTM4613 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 LTM4613
to achieve the low radiated EMI noise. Figure 7 shows a
typical example for the LTM4613 to meet the EN55022
Class B radiated emission limit.
Thermal Considerations and Output Current Derating
In different applications, LTM4613 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 thermal resistances reported in the Pin Configura-
tion section of the data sheet are consistent with those
parameters defined by JESD51-9. They are intended for use
with finite element analysis (FEA) software modeling tools
that leverage the outcome of thermal modeling, simula-
tion and correlation to hardware evaluation performed on
a µModule package mounted to a hardware test board.
This is also defined by JESD51-9, “Test Boards for Area
Array Surface Mount Package Thermal Measurements.”
The motivation for providing these thermal coefficients in
found in JESD51-12, “Guidelines for Reporting and Using
Electronic Package Thermal Information.”
Many designers may opt to use laboratory equipment
Figure 7. Radiated Emission Scan with 24V
IN
to
12V
OUT
at 8A Measured in 10 Meter Chamber
70
60
50
40
30
SIGNAL AMPLITUDE (dB uV/m)
20
10
0
30 226.2 422.4 613.6
FREQUENCY (MHz)
4613 F07
814.3 1010.0
–10
EN55022B LIMIT