LTM4641
APPLICATIONS INFORMATION—POWER SUPPLY FEATURES
The operation of MSP as a power interrupter provides a
critical element of robust OOV protection: it removes a
means for input power to flow through a damaged power
stagetoanypreciousloadsontheoutputvoltagerail, even
when input power is cycled.
•ꢀ Selectableꢀpulse-skippingꢀmodeꢀoperation
•ꢀ Outputꢀvoltageꢀsoft-startꢀandꢀrailꢀtracking
•ꢀ Power-upꢀintoꢀpre-biasedꢀconditionsꢀwithoutꢀsinkingꢀ
current from the output capacitors
•ꢀ Adjustableꢀswitchingꢀfrequency
•ꢀ Powerꢀgoodꢀindicator
•ꢀ RUNꢀenableꢀpin
For even greater resilience to a short-circuit between V
INH
andtheSWswitchingnodeofthepowerstage, anexternal
logic-level N-channel power MOSFET, MCB, is optionally
placed—in a crowbar configuration—on the output of
the power module. When an OOV condition is detected,
CROWBAR turns on MCB (within 500ns, maximum) to
dischargetheoutputcapacitorsandtransformanyresidual
energy in LTM4641’s power stage into a trivial amount of
heat—energy which would otherwise have only served
to inject charge into (further pump up the voltage on) the
output capacitors, where precious loads reside.
Novel and simple circuit implementations with LTM4641
and a few external components enable surge ride-
through protection and overtemperature detection of a
power-interrupt MOSFET. (See Figure 47, for example.)
The aforementioned features enabled by LTM4641 are
grouped by function and described in the remainder of
the Applications Information section.
The control and monitoring circuitry within the LTM4641
power module provide the following:
Power (V ) and Bias (V ) Input Pins
INH
INL
LTM4641’s power stage (VINH) and control bias (VINL
)
•ꢀ Fast,ꢀ accurate,ꢀ latchingꢀ outputꢀ overvoltageꢀ detectorꢀ
input pins are brought out separately to allow freedom
for implementing more sophisticated system configura-
tions, such as: fully utilizing LTM4641’s advanced output
overvoltage (OOV) protection features to protect the load
(e.g., front page schematic or Figure 46); providing rudi-
mentary input surge ride-through protection (Figure 47);
performing DC/DC down conversion from a power rail
below LTM4641’s inherent UVLO thresholds (from a 3.3V
bus in Figure 49).
(<500ns response time, < 12mv threshold error)
•ꢀ N-channelꢀoutputꢀovervoltageꢀcrowbarꢀpowerꢀMOSFETꢀ
drive
•ꢀ Accurateꢀ(<±2.4%)ꢀnonlatchingꢀandꢀresettableꢀlatchingꢀ
input overvoltage shutdown thresholds
•ꢀ N-channelꢀovervoltageꢀpower-interruptꢀMOSFETꢀdrive
•ꢀ Accurateꢀ(<±2.4%)ꢀInputꢀUVLOꢀrisingꢀandꢀUVLOꢀfallingꢀ
thresholds
If V
and V are powered from separate rails, it is
INL
INH
recommended to power up V prior to or concurrently
•ꢀ Built-inꢀ andꢀ adjustableꢀ overtemperatureꢀ shutdownꢀ
protection, programmable for resettable latching or
nonlatching (hysteretic restart) response
INL
with V . V should have a final value of at minimum
INH INL
3.5V within 2ms of V exceeding 3.5V. The recommen-
INH
INL
dation to sequence V ahead of or closely with V is
INH
•ꢀ Analogꢀtemperatureꢀindicatorꢀoutputꢀpin
not related at all to module device reliability but stems
rather from a desire to assure that the control section of
LTM4641 drives the MOSFETs in LTM4641’s power stage
•ꢀ Adjustableꢀpower-onꢀresetꢀandꢀtimeoutꢀdelayꢀtime
•ꢀ Latchoffꢀbehaviorꢀthatꢀcanꢀbeꢀalteredꢀtoꢀinsteadꢀprovideꢀ
deterministically whenever any appreciable V voltage
INH
autonomous restart after timeout delay time expires
is present. It is always permissible for V voltage to be
INL
•ꢀ Parallelableꢀforꢀhigherꢀoutputꢀpower
•ꢀ DifferentialꢀremoteꢀsensingꢀofꢀPOLꢀvoltage
•ꢀ Internalꢀloopꢀcompensation
present—regardlessofthestateofV —however,realize
INH
that there is no UVLO detection on V
.
INH
To prevent the control section from trying to regulate
through a dropout condition or commencing switching
•ꢀ Outputꢀcurrentꢀfoldbackꢀprotection
activityintheabsenceofV potential,itisrecommended
INH
4641f
17
Linear [ Linear ]
