LTM4641
OPERATION
Introduction
Power µꢁodule Regulator Reliability
TheLTM4641containsabuck-topologyregulatoremploy-
ing a constant on-time current mode control scheme,
including built-in power MOSFET devices with fast
switching speed and a power inductor. In its most basic
configuration (see Figure 45), the module operates as a
standalonenonisolatedswitchingmodeDC/DCstep-down
power supply. It can provide up to 10A of output current
with a few external input and output capacitors and output
feedback resistors. The supported output voltage range is
from0.6V DCto6V DC. The supported inputvoltage range
is4Vto38V,withamaximumstart-upvoltageof4.5V(over
temperature).Powerconversionfromlowerinputvoltages
can be realized if an auxiliary bias supply is available to
powerLTM4641’scontrolandhousekeepingbiasinputpin,
First and foremost, Linear Technology μModule products
adhere to rigorous testing and high reliability control,
fabrication, andmanufacturingprocesses—asisrequired
of all its products. Furthermore, as part of its commit-
ment to excellence, the Linear Technology Quality Control
program periodically updates its Reliability Data report
for LTM4600 series products to include cumulative data
obtained from ongoing and routine in-house testing relat-
ing to operational life, highly accelerated stress, power
and temperature cycling, thermal and mechanical shock,
and much more. To view the latest report visit http://www.
linear.com/docs/13557.
The LTM4641 easily supports high step-down ratios
with few external components. The additional protection
features when implemented provide an extra degree of
insurance beyond other μModule regulators.
V
. The LTM4641 Simplified Block Diagram is found in
INL
Figure 1. For a more detailed look, the Functional Block
Diagram is found in Appendix A, Figure 62.
Overview
ꢁotivation
When configured as shown in Figure 46, the LTM4641
can regulate an output voltage between 0.6V and 6V from
Pulsed loading conditions and abnormal disturbances
within the electrical systems found in industrial, vehicle,
aeronautic, and military applications can induce wildly
varying voltage transients (surges) on what is nominally
a 24V DC to 28V DC distributed bus (28V DC bus). The
duration of such disturbances can extend for periods of
time between a millisecond to a minute in length, with
excursions sometimes reaching (or exceeding) 40V and
falling below 6V.
an input voltage between 4V and 38V (4.5V start-up,
IN
maximum).
If an optional N-channel power MOSFET, MSP, is placed
between the input power source (V ) and the power
IN
stage input pins (V ), MSP’s role becomes that of a
INH
resettable electronic power-interrupt switch. The gate of
MSP is operated by V , and its gate-to-source voltage
ING
is assured to be clamped by a built-in 15V Zener diode
While switching buck regulators are of universal inter-
est due to their compact size and ability to deliver DC/
DC power conversion at high efficiency, FMEA (failure
modes and effects analysis) leads one to believe that
there is no way to reduce the severity rating and effects
of an electrical short from the input source to the output
load—howeverimprobable.TheLTM4641challengesthis
notion by protecting the load from seeing excessive volt-
age stress, even when its high side switching MOSFET
is short circuited.
accessed via V
. When switching action is engaged,
INGP
V
V
charges the gate of MSP to nominally 10V above
ING
INH
potential—suitablefordrivingastandard-logicMOS-
FET—and MSP becomes enhanced to pull V up to the
INH
input source supply’s electrical potential. The switching
regulator steps down V potential to V
when MSP is
INH
OUT
on. When switching action is inhibited by pulling the RUN
pin low or when a fault condition is detected by LTM4641’s
internal circuitry—such as an output overvoltage (OOV)
condition—the gate of MSP is discharged and MSP turns
off. The input source supply is thus disconnected from
LTM4641’s power stage input (V ).
INH
4641f
16
Linear [ Linear ]
