ltm4619 Linear Technology Corporation, ltm4619 Datasheet - Page 14

• Manufacturer Part Number: ltm4619
• Description: Dual, 26vin, 4a Dc/dc ?module Regulator
• Manufacturer: Linear Technology Corporation

LTM4619
APPLICATIONS INFORMATION
INTV
The INTV
LTM4619 internal circuitry and drives the power MOSFETs.
The input voltage of the LTM4619 must be 6V or above
for the INTV
the internal LDO dropout from the input voltage. For ap-
plications that need to operate below 6V input, then the
input voltage can be connected directly to the EXTV
pin to bypass the LDO dropout concern, or an external
5V supply can be used to power the EXTV
the input voltage is at high end of the supply range to
reduce power dissipation in the module. For example the
dropout voltage for 24V input would be 24V – 5V = 19V.
This 19V headroom then multiplied by the power MOSFET
drive current of ~15mA would equal ~0.3W additional
power dissipation. So utilizing an external 5V supply on
the EXTV
device temperature rise.
Slope Compensation
The module has already been internally compensated
for all output voltages. The Linear Technology μModule
Power Design Tool will be provided for control loop op-
timization.
Burst Mode Operation and Pulse-Skipping Mode
The LTM4619 regulator can be placed into high effi ciency
power saving modes at light load condition to conserve
power. The Burst Mode operation can be selected by fl oat-
ing the MODE/PLLIN pin, and pulse-skipping mode can
be selected by pulling the MODE/PLLIN pin to INTV
Burst Mode operation offers the best effi ciency at light
load, but output ripple will be higher and lower frequency
ranges are capable which can interfere with some systems.
Pulse-skipping mode effi ciency is not as good as Burst
Mode operation, but this mode only skips pulses to save
effi ciency and maintains a lower output ripple and a higher
switching frequency. Burst Mode operation and pulse-skip-
ping mode effi ciencies can be reviewed in graph supplied
in the Typical Performance Characteristics section.
14
CC
and EXTV
CC
CC
would improve design effi ciency and reduce
is the internal 5V regulator that powers the
CC
to regulate to the proper 5V level due to
CC
CC
pin when
CC
CC
.
Fault Conditions: Current Limit and Overcurrent
Foldback
The LTM4619 has a current mode controller, which inher-
ently limits the cycle-by-cycle inductor current not only in
steady-state operation, but also in transient.
To further limit current in the event of an overload condi-
tion, the LTM4619 provides foldback current limiting. If the
output voltage falls by more than 50%, then the maximum
output current is progressively lowered to one-third of its
full current limit value. Foldback current limiting is disabled
during the soft-start and tracking up.
Thermal Considerations and Output Current Derating
In different applications, the LTM4619 operates in a variety
of thermal environments. The maximum output current is
limited by the environmental thermal condition. Suffi cient
cooling should be provided to ensure reliable operation.
When the cooling is limited, proper output current derat-
ing is necessary, considering the ambient temperature,
airfl ow, input/output conditions, and the need for increased
reliability.
Two outputs of LTM4619 are paralleled to get high output
current for derating curve tests. The power loss curves in
Figures 7 and 8 can be used in coordination with the load
current derating curves in Figures 9 to 16 for calculating
an approximate θ
methods. Application Note 103 provides a detailed ex-
planation of the analysis for the thermal models and the
derating curves. Tables 2 and 3 provide a summary of the
equivalent θ
θ
and are improved with airfl ow. The junction temperature
is maintained at 125°C or below for the derating curves.
Safety Considerations
The LTM4619 modules do not provide isolation from V
V
with a rating twice the maximum input current needs to be
provided to protect each unit from catastrophic failure.
JA
OUT
parameters are correlated to the measured values,
. There is no internal fuse. If required, a slow blow fuse
JA
for the noted conditions. These equivalent
JA
for the module with various cooling
IN
4619f
to