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LTM4613

4613fd

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OPERATION

Power Module Description

The LTM4613 is a standalone nonisolated switch mode

DC/DC power supply. It can deliver 8A of DC output cur-

rent with minimal external input and output capacitors.

This module provides a precisely regulated output voltage

programmable via one external resistor from 3.3VDC to

15VDC over a wide 5V to 36V input voltage. The typical

application schematic is shown in Figure 18.

The LTM4613 has an integrated constant on-time current

mode regulator, ultralow RDS(ON) FETs with fast switching

speedandintegratedSchottkydiodes.Thetypicalswitching

frequencyis600kHzatfullloadat12Voutput.Withcurrent

mode control and internal feedback loop compensation,

the LTM4613 module has sufficient stability margins and

good transient performance under a wide range of operat-

ing conditions and with a wide range of output capacitors,

even all ceramic output capacitors.

Current mode control provides cycle-by-cycle fast current

limiting. Moreover, foldback current limiting is provided in

an overcurrent condition when VFB drops. Internal over-

voltageandundervoltagecomparatorspulltheopen-drain

PGOOD output low if the output feedback voltage exits a

±10% window around the regulation point. Furthermore,

in an overvoltage condition, internal top FET M1 is turned

off and bottom FET M2 is turned on and held on until the

overvoltage condition clears.

Input filter and noise cancellation circuitry reduce the

noise coupling to inputs and outputs, and ensure the

electromagnetic interference (EMI) meets the limits of

EN55022 Class B (see Figure 7).

Pulling the RUN pin below 1V forces the controller into

its shutdown state, turning off both M1 and M2. At light

load currents, discontinuous mode (DCM) operation can

be enabled to achieve higher efficiency compared to con-

tinuous mode (CCM) by setting FCB pin higher than 0.6V.

When the DRVCC pin is connected to INTVCC, an integrated

5V linear regulator powers the internal gate drivers. If a

5V external bias supply is applied on DRVCC pin, then an

efficiencyimprovementwilloccurduetothereducedpower

loss in the internal linear regulator. This is especially true

at the higher input voltage range.

The MPGM, MARG0, and MARG1 pins are used to sup-

port voltage margining, where the percentage of margin

is programmed by the MPGM pin, while the MARG0 and

MARG1 select positive or negative margining. The PLLIN

pin provides frequency synchronization of the device to

an external clock. The TRACK/SS pin is used for power

supply tracking and soft-start programming.

The typical LTM4613 application circuit is shown in Fig-

ure 18. External component selection is primarily deter-

mined by the input voltage, the maximum load current and

the output voltage. Refer to Table 2 for specific external

capacitor requirements for a particular application.

VIN to VOUT Step-Down Ratios

There are restrictions in the maximum VIN and VOUT step

down ratio that can be achieved for a given input voltage.

These constraints are shown in the Typical Performance

Characteristic curve labeled “VIN to VOUT Step-Down

Ratio.” Note that additional thermal derating may be ap-

plied. See the Thermal Considerations and Output Current

Derating section in this data sheet.

APPLICATIONS INFORMATION

Output Voltage Programming and Margining

The PWM controller has an internal 0.6V reference volt-

age. As shown in the Block Diagram, a 100k 0.5% internal

feedbackresistorconnectstheVOUTandVFBpinstogether.

Adding a resistor, RFB, from the VFB pin to the SGND pin

programs the output voltage.

VOUT =0.6V •

100k +RFB

RFB

or equivalently,

RFB =

100k

VOUT

0.6V

− 1

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