LTM4612
10
4612fc
OPERATION
Power Module Description
The LTM4612 is a standalone nonisolated switching mode
DC/DC power supply. It can deliver 5A of DC output
current with some external input and output capacitors.
This module provides precisely regulated output voltage
programmable via one external resistor from 3.3V
DC
to
15V
DC
over a 5V to 36V wide input voltage. The typical
application schematic is shown in Figure 18.
The LTM4612 has an integrated constant on-time current
mode regulator, ultralow R
DS(ON)
FETs with fast switching
speed and integrated Schottky diodes. The typical switching
frequency is 850kHz at full load at 12V output. With current
mode control and internal feedback loop compensation,
the LTM4612 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 while V
FB
drops. Internal over-
voltage and undervoltage comparators pull the open-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 I/O sides, and ensure the electromagnetic
interference (EMI) meets the limits of EN55022 Class B.
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 DRV
CC
pin is connected to INTV
CC
, an integrated
5V linear regulator powers the internal gate drivers. If a
5V external bias supply is applied on DRV
CC
pin, then an
efficiency improvement will occur due to the reduced power
loss in the internal linear regulator. This is especially true
at higher input voltages.
The MPGM, MARG0, and MARG1 pins are used to sup-
port output voltage margining, where the percentage of
margin is programmed by the MPGM pin, and the MARG0
and MARG1 select margining. The PLLIN pin provides
frequency synchronization of the device to an external
clock. The TRACK/SS pin is used for power supply track-
ing and soft-start programming.
The typical LTM4612 application circuit is shown in Figure
18. External component selection is primarily determined
by the maximum load current and output voltage. Refer
to Table 2 for specific external capacitor requirements for
a particular application.
APPLICATIONS INFORMATION
V
IN
to V
OUT
Stepdown Ratios
There are restrictions in the maximum V
IN
and V
OUT
step
down ratio that can be achieved for a given input voltage.
These constraints are shown in the Typical Performance
Characteristic curve labeled “V
IN
to V
OUT
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.
