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LTM4613

4613fd

For more information www.linear.com/LTM4613

APPLICATIONS INFORMATION

must be driven from a low impedance source such as a

logic gate located close to the pin. During the start-up of

the regulator, the phase-locked loop function is disabled.

INTVCC and DRVCC Connection

An internal low dropout regulator produces an internal

5V supply that powers the control circuitry and DRVCC

for driving the internal power MOSFETs. Therefore, if

the system does not have a 5V power rail, the LTM4613

can be directly powered by VIN. The gate driver current

through the LDO is about 20mA. The internal LDO power

dissipation can be calculated as:

PLDO_LOSS = 20mA • (VIN – 5V)

TheLTM4613alsoprovidestheexternalgatedrivervoltage

pin DRVCC. If there is a 5V rail in the system, it is recom-

mended to connect the DRVCC pin to the external 5V rail.

This is especially true for higher input voltages. Do not

apply more than 6V to the DRVCC 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 for

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 Configuration

section of the data sheet are consistent with those param-

eters defined by JESD51-12. 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.

The motivation for providing these thermal coefficients is

found in JESD51-12, “Guidelines for Reporting and Using

Electronic Package Thermal Information.”

Many designers may opt to use laboratory equipment

and a test vehicle, such as the demo board, to predict

the µModule regulator’s thermal performance in their

Figure 7. Radiated Emission Scan with 24VIN to

12VOUT at 8A Measured in 10 Meter Chamber

226.2

422.4

613.6

FREQUENCY (MHz)

4613 F07

814.3

1010.0

–10

EN55022B LIMIT

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